On Vibration Properties of Human Vocal Folds Svec, Jan

University of Groningen

On vibration properties of human vocal folds Svec, Jan

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Voice Registers, Bifurcations, Resonance Characteristics Development and Application of Videokymography

Jan G. Švec On Vibration Properties of Human Vocal Folds:

Voice Registers, Bifurcations, Resonance Characteristics, Development and Application of Videokymography

Proefschrift

ter verkrijging van het doctoraat in de Medische Wetenschappen aan de Rijksuniversiteit Groningen op gezag van de Rector Magnificus, dr. D.F.J. Bosscher, in het openbaar te verdedigen op woensdag 14 juni 2000 om 14.15 uur

door

Jan vec

geboren op 22 november 1966 te Olomouc, Tsjechoslowakije Promotor: Prof. dr. H.K. Schutte

Referent: dr. T. de Graaf

Beoordelingscommisie: Prof. dr. P.H. Dejonckere Prof. dr. T.D. Kernell Prof. dr. L.P. Kok

ISBN: 90-367-1235-1 Paranimfen: dr. ir. G.J. Verkerke M. de Waard

Dedicated to my grandfather, Frantiek Gaspar, in memory of whom I use the initial G in my name, and to my grandmother, Anna Gasparová. Publication of the thesis was financially supported by the Group for Study of Voice and Speech at the Palacký University in Olomouc, the Czech Republic under the project J14/98: N30000018 (coordinated by PhDr. J. Honová and doc. RNDr. J. Pešák, CSc.)

Cover page: Ivana Perůtková Lay-out: Miroslava Kouřilová Technical Assistance: Vladimír Kubák Printed in the Czech Republic at the Palacký University Press

Švec, Jan G. On Vibration Properties of Human Vocal Folds: Voice Registers, Bifurcations, Resonance Characteristics, Development and Application of Videokymography [Over trillingseigenschappen van menselijke stemplooien: stemregisters, bifurcaties, resonantiekenmerken, ontwikkeling en toepassing van videokymografie] Thesis University of Groningen, the Netherlands – With a summary in Dutch

Copyright © 2000: J. Švec, Olomouc, the Czech Republic All rights reserved. No part of this publication may be reprinted or utilized in any form by any electronic, mechanical or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission of the author.

ISBN: 90-367-1235-1 6

TABLE OF CONTENTS

Foreword ...... 8

Chapter 1: Introduction ...... 9

SECTION I: Voice Registers, Bifurcations, Resonance Characteristics of the Vocal Folds

Chapter 2: Vocal Breaks from the Modal to Falsetto Register by J. Švec & J. Pešák Folia Phoniatrica et Logopaedica, 46: 97–103 (1994) ...... 23

Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds by J. G. Švec, H. K. Schutte & D. G. Miller Journal of Speech and Hearing Research, 39(1): 135–143 (1996) ...... 33

Chapter 4: On Pitch Jumps Between Chest and Falsetto Registers in Voice: Data from Living and Excised Human Larynges by J. G. Švec, H. K. Schutte & D. G. Miller Journal of the Acoustical Society of America, 106(3): 1523–1531 (1999)...... 45

Chapter 5: Resonance Properties of the Vocal Folds: In Vivo Laryngoscopic Investigation of the Externally Excited Laryngeal Vibrations by J. G. Švec, J. Horáček, F. Šram & J. Veselý Journal of the Acoustical Society of America (in press)...... 57

SECTION II: Development and Application of Videokymography

Chapter 6: Videokymography: High-Speed Line Scanning of Vocal Fold Vibration by J. G. Švec & H. K. Schutte Journal of Voice, 10(2): 201–205 (1996) ...... 73

Chapter 7: First Results of Clinical Application of Videokymography by H. K. Schutte, J. G. Švec & F. Šram Laryngoscope, 108: 1206–1210 (1998)...... 81

Chapter 8: Variability of Vibration of Normal Vocal Folds as Seen in Videokymography by J. G. Švec, H. K. Schutte & F. Šram In: Dejonckere PH, Peters HFM (Eds.): Communication and Its Disorders: A Science In Progress. Proceedings 24th Congress International Association of Logopedics and Phoniatrics, Amsterdam, the Netherlands, August, 23–27, 1998. Vol. I. International Association of Logopedics and Phoniatrics: 122–125 (1999) ...... 89

Chapter 9: Videokymography: a New High-Speed Method for the Examination of Vocal-Fold Vibrations by J. G. Švec, F. Šram & H. K. Schutte Otorinolaryngologie a foniatrie /Prague/, 48(3): 155–162 (1999) ...... 95 7

Chapter 10 Addendum ...... 107

Summary and Conclusions ...... 113

Samenvatting en Conclusies ...... 119

Acknowledgments ...... 125

Curriculum Vitae ...... 127

List of publications of the author ...... 128

Bonus ...... 131 Foreword

FOREWORD

The research summarized in this book was initiated in 1990 when the author studied at the Department of Optics (head Prof. J. Peřina) and later on at the Department of Experimental Physics (head Prof. J. Pospíšil) of the Palacký University in Olomouc, the Czech Republic. At that time the author devoted his free time to playing music as a singer, guitar- and harmonica-player in an acoustic- jazz group Piano. The interest in music and voice led the author to initial experiments on singing voice which were done under the supervision of Dr. J. Pešák in the Laboratory for Logopedic Diagnostics at the School for Children with Impaired Speech in Olomouc-Kopeček and later also in the Electroacoustic Laboratory of the Neurologic Clinic (Medical Faculty, Faculty Hospital) and Institute of Biophysics (Medical Faculty) of the Palacký University. The main phase of the research, however, started during the research stay of the author at the Groningen Voice Research Lab of the University of Groningen, the Netherlands in 1993. Here the author had the opportunity to analyze and discuss the problem of singing voice in detail with specialists in this field (Prof. H. K. Schutte and D. G. Miller). Groningen Voice Research Lab enabled the author, for the first time, to use sophisticated experimental methods for examination of human voice and provided him with access to relevant literature on voice production, books and journals, which were not available in Czech libraries. The research originally devoted to voice registers and, especially, to the transition phenomena between chest and falsetto registers stimulated a search for a more powerful method for observation of the behavior of the vocal folds during these changes. This resulted in the development of a new laryngoscopic method, videokymography, during the second research stay of the author in Groningen in 1994 (in cooperation with H. K. Schutte and Lambert Instruments company). In 1995 the author moved to the Center for Communication Disorders, Medical Healthcom, Ltd. in Prague, the Czech Republic (directed by Dr. F. Šram). This Center provided the author with a well- equipped voice laboratory and made it possible for the first time to employ videokymography in clinical examination of patients with voice disorders. The worldwide positive response from the voice scientist, laryngologists and phoniatricians on the new possibilities offered by this method as well as the introduction of the method to the commercial market (by Kay Elemerics Corp) has lead to the situation when videokymography became a separate topic of the research carried by the author. The decade of 1990s brought into voice research the theory of nonlinear dynamics. This theory has provided new tools for interpreting phenomena related to, e.g., irregular, subharmonic or suddenly changing vocal-folds oscillations. Knowledge of bifurcation phenomena introduced by this theory enabled the author to progress also in the search for a scientific interpretation of the phenomena related to transitions between chest and falsetto voice registers. The close cooperation of the author with the University of Groningen during the years 1993–2000 has been possible via support from various foundations and research grants (listed in Acknowledgments) and enabled to finish the dissertation in the present form. Chapter 1: Introduction

CHAPTER 1

Introduction

Švec: On Vibration Properties of Human Vocal Folds 11

Introduction

There are two main aims of the dissertation:

• to provide new information on discontinuities in the transition between chest and falsetto voice registers. (As shown here, the question of transition between chest and falsetto registers is highly complex and addresses the problem of the basic underlying mechanism of the vocal-fold vibration).

• to develop a (cost-friendly) method which would provide more detailed information on the vibratory behavior of the vocal folds. The need for a new method arose from the fact that currently available methods visually observing vocal-fold vibrations are either not capable of observing fast phenomena (stroboscopy), or are not easily available due to the high costs (high-speed imaging systems).

In accordance with these two aims, the dissertation is divided in two sections. The first part brings original experiments exploring phenomena related to abrupt chest-falsetto transition and provides new information on resonance properties of the vocal folds. The second part describes development and application of an original method, called “videokymography,” for examination of vocal fold vibration.

SECTION I: Voice registers, bifurcations, resonance 133], (c) interaction of the subglottal and supraglottal properties of the vocal folds resonances with the vocal-fold oscillations [3; 91; 119; 122], as well as (d) the perceptual factors [23; 24;76; Chest and falsetto voice registers 84; 113; 122]. In this book the attention is focused When a naïve (particularly male) singer sings an mainly on the role of the vocal folds. ascending scale with a moderate loudness, around the It has been known that the chest and falsetto frequency of ca. 300–350 Hz (tones D4 – F4) he reaches registers differ in the amount of tissue which is a point of instability where the voice “breaks” (e.g., [41; incorporated in the vibration of the vocal folds [11; 94; 95; 122]). Pitches above this limit cannot be sung in 12; 15; 32; 40; 90; 99; 104; 108]. In the simplest the same way but only with a different, “thinner,” voice representation, the vocal fold is divided in two tissue quality. The division of the singing voice into two gross layers, “cover” (created by mucosa and ligament of parts is an important issue in (professional) singing the vocal fold) and “body” (mostly created by the which has been described already for centuries (for thyroarytenoid, TA, muscle) [56; 57]. In chest register, historical overview see, e.g., [82; 109]). These two both the body and cover participate in the vibration of qualities of voice have been traditionally designated as the vocal folds while in falsetto only the cover is “chest” (or “modal”) and “falsetto” registers, even if involved [56; 57; 60; 125; 126] (Fig. 1). In falsetto, the the terminology problem is far from resolved. The frequency is increased mostly passively, by longitudinal problem of voice registers represents one of the most stretching (elongating) the cover of the vocal folds by controversial and least-understood topics of singing means of the activity of the cricothyroid (CT) muscle, voice. The physiological reason for the division of the whereas when raising the frequency in the chest register, singing voice into the chest and falsetto registers has not the stretching of the vocal fold cover is accompanied been sufficiently explained yet. also by an active contraction of the TA muscle forming Valuable overviews on registers from a scientific the body of the vocal fold [11; 56; 57; 59; 60; 62; 122; point of view can be found, e.g., in publications of van 126; 129]. den Berg [11; 12]; Large [82]; Hollien [65]; van Deinse The differences between the chest and falsetto [128]; Hirano [59]; and Titze [122]. Among the registers are reflected in specific vibratory patterns of potential factors that can play a role for the occurrence the vocal folds —the chest register is characterized by of the voice registers, there are (a) the mechanism of more pronounced vertical phase differences [5; 56; 57; oscillation of the vocal folds [12; 15; 32; 56; 82; 99; 104; 107; 122], larger contact area [80; 102; 106; 132], 104; 122], (b) resonance of the vocal tract [82; 93; larger closed quotient1 [58; 80; 122], and lower

1 Closed quotient (CQ) is calculated as the duration of the closed phase of the vocal folds divided by the duration of the whole vibratory cycle [58;98;117]. Sometimes instead of closed quotient an open quotient (OQ) is used, which is calculated as the duration of the open phase of the vocal folds divided by the duration of the whole vibratory cycle. (The open quotient is closely related to the closed quotient since it holds OQ + CQ = 1) 12 Chapter 1: Introduction

Fig. 1. A schematic, simplified view frequency of the vocal-fold vibration, of the vocal folds (frontal section). in more detail. Philosophically taken, In chest register the whole vocal folds vibrate, including the understanding better the underlying thyroarytenoid (TA) muscle principle of the register jumps should forming the “body” of the vocal be helpful also in understanding the folds, while in falsetto register only mechanism of a smooth register the edges (cover, C) of the vocal folds participate in the vibration. transition which is based on eliminating In falsetto register the frequency is these abrupt changes. raised mostly passively by increasing Titze [120; 122] formulated, on the tension of the cover through a basis of investigations of several elongation of the vocal folds. [Here the activity of the cricothyroid, CT, authors, two hypotheses on the possible muscle (not illustrated here) is mechanism of the spontaneous register considered to play an important transitions: role]. For increasing the frequency A) the sudden change from chest to of the chest register the stretching of the cover is accompanied also by falsetto arises due to a sudden an active contraction of the TA spontaneous relaxation of the TA muscle. muscle (maximum active thyroarytenoid stress hypothesis). This change happens spontaneously especially at high fundamental frequencies, although there is a consi- frequencies of the chest register in which the activity derable range of fundamental frequencies where the of the TA muscle reaches the maximal value that two registers overlap in most voices. (See, e.g., Fig. 2 cannot be sustained any longer. in Chapter 8 for an example of the two different B) interaction of the subglottal (tracheal) resonance vibratory patterns). with the voice source negatively influences the vocal One of the practical singing issues is the problem of fold oscillation at specific phonational pitches and the transition between the chest and falsetto registers causes a change in the resulting voice quality (subglottal in singing. Different singing styles approach the resonance hypothesis). register transition differently. The western operatic As Titze noted, however, from these two, only the singing tradition aims at eliminating any discontinuity first hypothesis would explain also the sudden changes by “equalizing” the registers, reaching a “smooth of fundamental frequency observed during the chest- register transition” and a “uniform voice quality” falsetto jumps [120]. across the whole range of singing (e.g., [41; 82; 83; 86; Abrupt frequency changes are not exclusively 94]). A successful accomplishment of this goal usually related to voice only. A well-known example can be requires a lot of practice. An “improperly balanced” taken from a simple musical instrument – a flute. voice leads to an involuntary spontaneous “register When an input air pressure of (or the airflow velocity break” or “abrupt register transition.” Such an abrupt in) a flute is continuously increased, the original tone register transition is usually accompanied by a spon- suddenly leaps into another, higher frequency taneous sudden change (leap, jump) of frequency [22; (“overblown-flute phenomenon”) [29; 31; 130; 131]. 102–104]. This effect is known to be caused by existence of While the western operatic tradition considers such a number of resonance frequencies of the flute. When sudden changes accidents to be avoided, some other “overblown,” the pitch jumps from a lower to a higher singing traditions—for example yodeling and country resonance frequency. Since the resonance frequencies and western—voluntarily exploit the chest-falsetto reflect the given setup of the flute [29; 31; 112; 114], jumps in a controlled way for artistic purposes. The the frequency jump reflects inherent information on chest-falsetto jumps are also related to specific voice the flute properties. This leads us to express a hypo- disorders, such as “mutational dysphonia,” and are thesis that the pitch jumps observed during the chest- generally known as pitch jumps occurring falsetto transition might, analogously, reflect inherent spontaneously and out of control during speech [44; vibration properties of the vocal folds and be related 100; 134]. to their resonance frequencies. Very few objective data on the chest-falsetto The aim of Chapter 2 was to explore experimentally discontinuity have been available. The original goal of whether the “overblown flute” analogy can be adapted the research presented in this book was to investigate for studying the properties of the voice source. Two the mechanism of the spontaneous sudden changes of main questions of the chapter are: Švec: On Vibration Properties of Human Vocal Folds 13

1) Is it possible to elicit pitch jumps in voice mean airflow rate values were measured via analogously as in a flute, i.e., by increasing the pneumotachography. phonatory airflow and “overblowing” the voice source to a different frequency? Theory of nonlinear dynamics and bifurcation phenomena 2) If yes, what is the magnitude of the frequency In 1990s, the theory of nonlinear dynamics was change? (In a flute, the frequencies after and before introduced in voice physiology/pathology and applied the leap are approximately related by an integer- to explain phenomena related to irregularities, number ratio, i.e., 2:1, 3:2, 4:3, etc. What is the subharmonic oscillations and sudden changes in vocal ratio in the vocal folds?) fold behavior [1; 4; 6; 7; 30; 47; 48; 54; 92; 123]. It has A voice maneuver was utilized in which chest- been realized that the voice source presents a highly falsetto pitch jumps were elicited by smoothly nonlinear vibratory system. Nonlinearity has been increasing the phonatory airflow while slightly found, e.g., in elastic properties of the vocal-fold tissues abducting the vocal folds. The magnitudes of pitch (stress-strain characteristics [25; 57; 71; 123; 124]), in jumps were measured and documented throughout the pressure-flow relation in the glottis [68; 123] or in the whole frequency range in a normal male subject. collision of the vocal folds during their vibration [68]. Besides chest-falsetto jumps, also production of an It has been shown that voice source exhibits

F0/2 subharmonic frequency (sounding an octave below phenomena that are similar to effects known from the the original tone) was observed in the experiment. theory of nonlinear dynamics [47; 52; 54; 69; 70; 92; The occurrence of a subharmonic frequency evokes a 110]. The theory also introduced new methods for question on how the subharmonic phonation is created analysis of the vocal fold vibration [6; 8; 9; 46 ;49–51; in the vocal folds? Most often it has been assumed 89; 123]. that such a vibratory pattern results from One of the typical effects known from the theory of desynchronization of the oscillations of the left and nonlinear dynamics is termed a “bifurcation.” This right vocal folds, especially in pathological cases [69; term designates a sudden qualitative change in the 70; 77; 110; 122; 123]. Here, however, the subharmonic behavior of a nonlinear dynamic system induced by a frequency arose in non-pathologic vocal folds in which gradual, smooth change of an input parameter [16; no large asymmetry is presumed. Models predicted 96; 123]. Studies with vocal-fold models have already that the subharmonic pattern might also have other indicated that various register transitions might be origins than asymmetry and could arise with both the explained as bifurcations [47; 88]. Also, experiments vocal folds synchronized [18; 54]. Information on the with excised canine larynges indicate the bifurcation oscillation of true, non-pathological vocal folds origin of the spontaneous register transitions [19;107]. responsible for such a phonation has been missing, Chapter 4 explores a bifurcation hypothesis on the however. One of the main reasons for the lack of mechanism of chest-falsetto jump, which presents an information have been the difficulties of routinely alternative to the Titze’s hypothesis of maximum active available videostroboscopic systems with investigating thyroarytenoid stress: the abrupt chest-falsetto transition phonations deviating from a simple periodic vibratory can arise spontaneously, without any necessary sudden pattern (see Section II, below). change in adjustment of the laryngeal muscles. Chapter 3 describes the phonatory maneuver, Data from the van den Berg instructional film The designed in chapter 2, in more detail and devotes the Vibrating Larynx [15], showing abrupt chest-falsetto attention to the behavior of the vocal folds during the transitions in an excised human larynx, were analyzed. subharmonic phonation. In order to provide the The film demonstrates some experiments on excised complete, detailed description of the subharmonic human larynges carried at the University of Groningen vibratory pattern of the vocal folds, a video- in the late 1950s by van den Berg and Tan [10; 12–15; laryngostroboscopic setup was modified by 115]. In their pilot experiments, the abrupt register constructing a special electronic divider which allowed transitions were noticed, but not analyzed in detail. to track the subharmonic frequency. Laryngo- Besides the excised larynx, the chapter investigates stroboscopic images were obtained, documenting the the chest-falsetto leaps in three singers (one female shapes of the vocal folds during the subharmonic and two male) and returns to the question of the vibratory cycle in detail. Besides the magnitude of the frequency leap during the chest- laryngostroboscopic images, the vibratory pattern of falsetto transition. Differences in the magnitudes are the vocal folds was documented also by means of studied among the three singers. The chapter offers electroglottography and photoglottography and the a new approach of quantifying the chest-falsetto 14 Chapter 1: Introduction

Fig. 2. Schematical illustration of a normal cycle of the vocal fold vibration. The oscillating vocal folds modulate a stream of air coming from the lungs and trachea, and determine the primary voice signal. Note that the vibration of the vocal folds is not purely opening-closing, but encorporates differences along the vertical dimension of the vocal folds (the lower part of vocal folds opens and closes earlier than the upper part; a phenomenon called “vertical phase difference”). See also Fig.1 in Chapter 7 and Fig. 4 in Chapter 9 for more details. transition using narrow-band spectrograms and vibration [18; 67; 111; 121; 122]. The two basic electroglottography and provides a new concept for eigenmodes can be most easily demonstrated by further studies on these phenomena. considering a simple two-mass model of the vocal folds [68] whose behavior has proven to well Eigenmodes of vibration of the vocal folds approximate the periodic behavior of the true vocal Theoretically, vibration of any (even a very complex) folds under normal conditions. (For an illustration of structure can generally be explained as a superposition a normal vibratory pattern of the vocal folds see Fig. 2). of independent characteristic vibratory patterns, called The model divides each vocal fold into two sections, eigenmodes [2]. Like any other vibrating structure, representing the upper and lower part, which are vocal folds have inherent eigenmodes, each of which modeled as two spring-mass oscillators (Fig. 3). is associated with a specific eigenfrequency [17; 18; A separate spring is used to couple the two masses. 20; 21; 27; 118; 122; 127]. These eigenmodes represent Figure 3 depicts the two characteristic eigenmodes of the key elements which are crucial for the resulting this model (images A, B versus C, D). Under normal vibratory pattern. In order to understand in detail the conditions, these two eigenmodes vibrate at an mechanism of various vibratory patterns of the vocal identical frequency (a phenomenon called “1:1 folds, such as those responsible for different voice entrainment” of the modes) and their combination registers, detailed information on the eigenmodes and results in a simple periodic vibration of the vocal folds eigenfrequencies of the vocal folds is needed. which closely approximates the one shown in Fig. 2. If Information on eigenmodes and eigenfrequencies can the two modes are adjusted to vibrate at different also be utilized, e.g., for a proper adjustment of frequencies, the model can produce various kinds of numerical models of the vocal folds (e.g., [26; 87]). subharmonic and irregular vibratory patterns [7; 47; Data on these characteristics have been rather limited, 52]. however, mostly due to difficulties related to their In contrast to the two-mass model, the vibratory measurement in the delicate and hardly accessible behavior of which is represented by only two vocal fold tissues. eigenmodes, in the tissues of the true vocal folds there Chapter 5 addresses the very basic general problem theoretically exist an infinite number of eigenmodes related to the eigenmodes and eigenfrequencies. Until [17; 18; 20; 21; 122; 127] (Fig. 4). Various combinations recently, most of the information on eigenmodes of of these eigenmodes could theoretically produce vocal folds has been derived from theory and from a great variety of vibratory patterns of the vocal folds. numerical models of the vocal folds. There are two The identification of the specific modes responsible eigenmodes of the vocal folds which have been for different kinds of vocal-fold vibratory patterns is considered to play a dominant role for the vocal-fold a highly important problem of the basic voice science Švec: On Vibration Properties of Human Vocal Folds 15 of today which also promises to provide an insight into the basic mechanism of voice registers [17; 18; 53]. Chapter 5 designs an experiment for the investigation of the eigenmodes and eigenfrequencies in living vocal folds by means of laryngoscopy. A resonance approach known from technical studies of vibration of complex structures [2; 101], previously utilized by Kaneko [72–75] for the measurement of resonance frequencies of the vocal folds, has been employed and modified for a laryngoscopic setup. The eigenmodes/eigenfrequencies were identified as resonance modes/resonance frequencies of the vocal folds. The vocal-fold oscillations were excited externally at various frequencies using a shaker placed on a neck of a living male subject (the same subject as investigated in Chapters 2 and 3). The vibratory shapes of the vocal folds (i.e., the mode shapes) were examined Fig. 3. Two characteristic eigenmodes of vibration of the two-mass model laryngoscopically in stroboscopic light. of the vocal folds: x-10 (A and B) and x-11 (C and D) [For explanation of An original method called videokymography, the assignment of the modes see the legend in Fig. 4]. The vocal folds are newly developed by the author for examination shown at two opposite phases of a vibratory cycle. of the vocal-fold vibration (see Section II), was employed for examination of the resonance frequencies of the vocal folds. The experiment allowed, for the first time, to visualize the characteristic modes of vibration in living vocal folds and to relate these modes to the specific resonance frequencies of the vocal folds.

SECTION II: Development and application of videokymography Voice irregularities, diplophonia, subharmonic phonation, or abrupt register transitions – information on vibration of the vocal folds in these cases has been to a large extent missing. One of the fundamental reasons for the lack of Fig. 4. Theoretical mode shapes of vibration of three low-order eigenmodes information is that the routinely available of the continuous model of the vocal folds: x-10, x-11 and x-21. An methods of the laryngeal examination which artificial separation of left and right folds is used for illustrative purposes. provide direct view of the vocal folds, such as In the x-ij notation “x” designates oscillations in the lateral-medial direction videolaryngoscopy and videolaryngostroboscopy, and the i,j indices give number of oscillatory half-wavelengths occurring along the horizontal and vertical dimensions of the vocal folds, respectively. are not able to capture the fast changes of the The modes x-10 and x-11 here are analogous to those in the two-mass vocal-fold vibration in these cases (e.g., [61], see model of the vocal folds shown in Fig. 3. The mode x-21 is assumed to also below). On the other hand, there exist very contribute to more complex (irregular or pathological) vibration patterns powerful high-speed cinematographic systems of the vocal folds [18;118;123]. (Figure adapted after Berry et al., 1994 [18]). [28; 58; 63; 97; 105; 116; 135] and high-speed digital imaging systems [45; 55; 64; 66; 78; 79; Gall et al. [37] introduced a method “photokymography,” 81; 85; 136] which are capable of capturing the which was capable of investigating irregular oscillations of irregularities of the vocal-fold vibration; these the vocal folds and which was based on a different principle systems remain, however, very expensive and (Fig. 5). Although the images from photokymography are inaccessible for most voice laboratories and appeared very promising for a more detailed investigation clinics. of the vocal-fold vibration [33–39; 42; 43], the system 16 Chapter 1: Introduction

encountered together with Prof. Schutte and the Lambert technical problems Instruments BV company (Leutingewolde, the and has never Netherlands) into a practical system. The video- developed into a kymographic system was designed as a cost-friendly, commercially simple alternative of a high-speed imaging system available form. suitable for the examination of vocal-fold vibrations. There has been a The paper describes the principle of the method and need for a new cost- presents the very first videokymographic images of friendly method the vibrating vocal folds obtained from 2 normal male which would enable subjects. the observation of all Chapter 7 brings the first results of clinical kinds of the vocal- application of videokymography. In the first part, Fig. 5. Photokymography. A moving fold oscillation not videokymographic images of a normal subject are slit is placed in front of a photo- limited to periodic or related to the stroboscopic images. In the second graphic film which enables to record slow-changing part, the first videokymographic images of vocal folds vocal-fold vibration. (After Gall & Hanson, 1973 [38]). oscillations of the in patients with selected voice disorders (unilateral vocal folds. In Fig. 6 vocal fold paralysis, vocal fold edema, vocal fold polyp, a short explanation of partial cordectomy) are shown. Videokymography is the differences among the currently available optical presented as a complementary method to video- methods is given. laryngostroboscopy. Laryngoscopic, laryngostrobo- Chapter 6 introduces a new examination method scopic and videokymographic images of a single patient “videokymography,” which was originally designed by are composed together making it possible to effectively the author in Groningen in 1994 and developed document the most important laryngeal findings. It is

Fig. 6. Schematic illustration of differences among optical methods (standard video, videostroboscopy and high-speed imaging) registering fast vibration. For simplicity, the extent of displacement of the vibration is digitized to 7 levels (marked by horizontal lines). The image rate of a standard video camera is slower than the frequency of the investigated (vocal-fold) vibration (A; here three cycles fall within a single video image). Under continuous light, the standard video camera registers, like the eye, only a blurry image (D; it encompasses all the positions of the vocal folds that occurred within the integration time of a single video image). If stroboscopic light is used, which creates an illusory slowed-down impression of the vibration (dots in A), the resulting video image corresponds to C. The video camera registers the illusory slow motion; the single successive images could be slightly fuzzy if more than one light flash fall within a single image (ca. 3 flashes per image are registered here). In contrast to the methods C and D, the high-speed imaging (B) works with image-rates higher than the frequency of the observed vibration and captures the true vibratory behavior of the vocal folds. The high-speed rate enables to capture also fast changes of vibration occurring from cycle to cycle (not illustrated here) that would not be revealed by the methods C and D. Švec: On Vibration Properties of Human Vocal Folds 17 shown how the method of composition of such different REFERENCE LIST images can be helpful in revealing the mechanism of [1] Vocal fold physiology: controlling complexity and chaos. a voice disorder in more detail. Davis PJ, Fletcher NH, editors. 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SECTION I: Voice Registers, Bifurcations, Resonance Characteristics of the Vocal Folds Chapter 2: Vocal Breaks from the Modal to Falsetto Register by J. Švec & J. Pešák FoliaŠvec: PhoniatricaOn Vibration et Properties Logopaedica, of Human 46: 97–103 Vocal (1994) Folds 23

CHAPTER 2

Vocal Breaks from the Modal to Falsetto Register

Švec J., Pešák J.

The author would like to express his thanks to the anonymous reviewer of Folia Phoniatrica et Logopaedica who was enormously helpful in improving the manuscript. Švec: On Vibration Properties of Human Vocal Folds 25

J. Švec, J. Pešák 26 Chapter 2: Vocal Breaks from the Modal to Falsetto Register Švec: On Vibration Properties of Human Vocal Folds 27 28 Chapter 2: Vocal Breaks from the Modal to Falsetto Register Švec: On Vibration Properties of Human Vocal Folds 29

4 30 Chapter 2: Vocal Breaks from the Modal to Falsetto Register Švec: On Vibration Properties of Human Vocal Folds 31 32 Chapter 2: Vocal Breaks from the Modal to Falsetto Register Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds by J. G. Švec, H. K. Schutte & D. G. Miller Journal of Speech and Hearing Research, 39(1): 135–143 (1996) Švec: On Vibration Properties of Human Vocal Folds 33

CHAPTER 3

A Subharmonic Vibratory Pattern in Normal Vocal Folds

Švec J. G., Schutte H. K., Miller D. G.

Švec: On Vibration Properties of Human Vocal Folds 35 36 Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds Švec: On Vibration Properties of Human Vocal Folds 37 38 Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds Švec: On Vibration Properties of Human Vocal Folds 39 40 Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds Švec: On Vibration Properties of Human Vocal Folds 41 42 Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds Švec: On Vibration Properties of Human Vocal Folds 43 44 Chapter 3: A Subharmonic Vibratory Pattern in Normal Vocal Folds Chapter 4: On Pitch Jumps Between Chest and Falsetto Registers in Voice: Data from Living and Excised Human Larynges by J. G. Švec, H. K. Schutte & D. G. Miller Journal of the Acoustical Society of America, 106(3): 1523–1531 (1999)

CHAPTER 4

On Pitch Jumps Between Chest and Falsetto Registers in Voice: Data from Living and Excised Human Larynges

Švec J. G., Schutte H. K., Miller D. G.

Švec: On Vibration Properties of Human Vocal Folds 47 48 Chapter 4: Chest-falsetto jumps Švec: On Vibration Properties of Human Vocal Folds 49 50 Chapter 4: Chest-falsetto jumps Švec: On Vibration Properties of Human Vocal Folds 51 52 Chapter 4: Chest-falsetto jumps Švec: On Vibration Properties of Human Vocal Folds 53 54 Chapter 4: Chest-falsetto jumps Švec: On Vibration Properties of Human Vocal Folds 55 56 Chapter 4: Chest-falsetto jumps Chapter 5: Resonance Properties of the Vocal Folds: In Vivo Laryngoscopic Investigation of the Externally Excited Laryngeal Vibrations by J. G. Švec, J. Horáček, F. Šram & J. Veselý Journal of the Acoustical Society of America (in press)

CHAPTER 5

Resonance Properties of the Vocal Folds: In Vivo Laryngoscopic Investigation of the Externally Excited Laryngeal Vibrations

Švec J. G., Horáček J., Šram F., Veselý J.

Švec: On Vibration Properties of Human Vocal Folds 59

Resonance Properties of the Vocal Folds: In Vivo Laryngoscopic Investigation of the Externally Excited Laryngeal Vibrations

Jan G. Švec a, Jaromír Horáček b, František Šram a, and Jan Veselý b

a Center for Communication Disorders, Medical Healthcom, Ltd., Řešovská 10/491, 181 00 Prague 8, the Czech Republic Tel/Fax: (420-2)-855 03 39, E-mail: [email protected]

and

b Institute of Thermomechanics, Academy of Sciences of the Czech Republic, Dolejškova 5, 182 00 Prague 8, the Czech Republic

ABSTRACT

The study presents the first attempt to investigate resonance properties of the living vocal folds by means of laryngoscopy. Laryngeal vibrations were excited via a shaker placed on the neck of a male subject and observed by means of videostroboscopy and videokymography (VKG). When the vocal folds were tuned to the phonation frequency of 110 Hz and sinusoidal vibration with sweeping frequency (in the range 50 - 400 Hz) was delivered to the larynx, three clearly pronounced resonance peaks at frequencies around 110, 170 and 240 Hz were identified in the vocal fold tissues. Different modes of vibration of the vocal folds, observed as distinct lateral- medial oscillations with one, two and three half-wavelengths along the glottal length, respectively, were associated with these resonance frequencies. At the external excitation frequencies below 100 Hz, the vibrations of the ventricular folds, aryepiglottic folds and arytenoid cartilages were dominant in the larynx.

PACS numbers: 43.70.Aj, 43.40.At, 43.40.Ng, 43.20.Ks, 43.25Gf,

INTRODUCTION Titze and Strong (1975) were the first who From the theory of vibration it is known that theoretically studied the eigenmodes of the vocal folds. vibration of a structure can generally be decomposed The theory predicts generally infinite number of into a set of independent characteristic vibration eigenmodes in the vocal-fold tissues (e.g., Titze and patterns, called eigenmodes. Like any other vibrating Strong, 1975, Titze, 1994). Only a few dominant structure, vocal folds have inherent eigenmodes which (lowest) modes, however, are assumed to play a sub- are crucial in determining their possible vibration stantial role in the actual vibration of the vocal folds. behavior. Each of the eigenmodes is associated with In a study with a finite-element model of the vocal a specific eigenfrequency and exhibits certain damping. folds, Berry et al. (1994) have found that combination The eigenmodes, eigenfrequencies and damping are of only two eigenmodes captures more than 95% of called the “dynamic characteristics” of the vibrating the variance of the vocal-fold vibration in normal system and are independent of the excitation phonation and more than 70% of irregular vocal-fold mechanism of the vibration. These characteristics can vibration. Prevalence of two dominant eigenmodes be used to describe inherent vibration properties of has been recently found also experimentally in the vocal folds. Information on the dynamic vibration of the vocal folds in excised canine larynges characteristics of the true vocal folds has been rather (Berry, in review). limited, however, mostly due to difficulties related to The two dominant eigenmodes have been measurement of these characteristics in the delicate theoretically known and designated as x-10 and x-11 and hardly accessible vocal fold tissues. (see footnote). The x-10 mode presents a lateral-medial 60 Chapter 5: Resonance Properties of the Vocal Folds oscillation which is responsible for opening and closing was registered by means of modified ultrasonic of the vocal folds in a vibratory cycle. The x-11 mode equipment. Kaneko designed a special phonatory presents an out-of phase motion of the upper and maneuver in order to investigate the eigenfrequencies lower margins of the vocal folds, which plays an of the vocal folds in living subjects: the subject important role in the transfer of the aerodynamic phonated at a given pitch and stopped delivering the energy into the motion of the vocal fold tissues air from the lungs while keeping the vocal folds in the (Stevens, 1977, Ishizaka, 1988, Titze, 1988). Higher- phonatory position (so called “neutral phonatory order modes, such as, e.g., x-20, x-21 or x-30, x-31 position”). At that moment the shaker was switched (lateral-medial oscillations encompassing two or three on and the response measurement was done. Kaneko half-wavelengths along the glottal length) are assumed identified two distinct eigenfrequencies of the vocal to partially contribute to production of more complex folds, which changed with the phonation frequency. vocal-fold vibration patterns, especially those related The lower of the eigenfrequencies was found to be to pathologic voice quality (Titze and Strong, 1975; close to the frequency of phonation. Similar results Titze, 1994; Berry et al., 1994) were obtained by Kaneko et al. in number of living During phonation, the oscillation of the vocal folds subjects as well as in excised human larynges. is significantly influenced by phonatory airflow. The eigenfrequencies of the true vocal folds Aerodynamic coupling leads, along with inherent measured by Kaneko et al. correspond well to the nonlinearity of the vocal folds, to phenomena such as eigenfrequencies of the two-mass model of the vocal entrainment of the eigenmodes (also known as “mode- folds designed by Ishizaka and Flanagan (1972). On locking”), which cause rearrangement of the the basis of this correlation it has been hypothesized eigenfrequencies of the vocal folds (Berry et al., 1994; (Ishizaka, 1988) that these two eigenfrequencies are Fletcher, 1996; Berry, in review). A well known related to the eigenmodes x-10 and x-11. Recently, example can be found in the behavior of a simple two- however, this hypothesis has been challenged by Berry mass model of the vocal folds (Ishizaka and Flanagan, and Titze (1996) who have, on the basis of a theoretical 1972): under typical conditions the eigenmodes of the analysis of a continuum model of the vocal folds, model, which correspond to the modes x-10 and x-11, predicted the eigenfrequencies of the x-10 and x-11 are tuned to 120 and 201 Hz (e.g., Titze, 1976; Ishizaka, modes to be nearly identical. Much smaller difference 1988). Under the influence of the airflow these two (0-25 Hz) than that measured by Kaneko et al. (ca. 50- eigenmodes are entrained to vibrate at identical 100 Hz) was also found between the eigenfrequencies frequency around 130-150 Hz (depending on the of the x-10 and x-11 modes in the finite-element model subglottal pressure, see Ishizaka and Flanagan, 1972). of the vocal folds by Dedouch et al. (1999). The This effect illustrates a need for studies of vocal fold eigenfrequencies of eigenmodes found in the finite- behavior not influenced by the phonatory airflow element model of Jiang et al. (1998) were, on the revealing the dynamic characteristics more accurately. other hand, quite far apart (>100 Hz). Unfortunately, Only a few experimental studies have been devoted Kaneko’s experiments did not bring any information to the vibrations of the vocal folds without the airflow. on mode shapes of vibration of the vocal folds and In a study with excised human larynges, Tanabe et al. thus it has not been clear whether, indeed, the (1979) displaced a vocal fold via a metal plate attached measured eigenfrequencies belong to x-10 and x-11, to a stretched elastic rod. When the rod was cut, the or to some other eigenmodes. This uncertainty has vocal fold was released and exhibited a damped called for new, more specific measurements of the oscillation which was monitored using a high-speed dynamic characteristics of the true vocal folds. (cinematographic) camera. These experiments were This study presents the first attempt to investigate performed for obtaining information on the damping the dynamic characteristics of the vocal folds in vivo properties of the vocal folds. The results could, in laryngoscopically. The basic question of the present principle, have been used also for studying the study is the following one: Is it possible to externally eigenfrequencies of the vocal folds, but these authors induce the vibration of the vocal folds to such extent did not determine these values. that they can be monitored laryngoscopically? The only studies to date, which provide information Certain positive evidence can be found in the studies on eigenfrequencies as well as damping characteristics of Fukuda et al. (1987) and Fukuda (1993). Here, of the true vocal folds, were published by Kaneko et a laryngeal shaker, principally similar to the one used al. (1981, 1983, 1987). Here, the vibration of the vocal by Kaneko, was used to excite the vocal-fold vibrations folds was excited externally using a shaker placed on in patients undergoing surgery under general the thyroid cartilage. The response of the vocal folds anesthesia. The vibration of the vocal fold mucosa Švec: On Vibration Properties of Human Vocal Folds 61 could be observed laryngoscopically under stroboscopic light. The studies of Fukuda were, however, clinically oriented and did not pay attention to the dynamic characteristics of the vocal folds. The aim of the present study is to employ the laryngoscopical observation 1) to identify the eigenfrequencies of the vocal folds and 2) to relate these eigenfrequencies to the specific mode shapes of vibration.

I. MATERIALS AND METHODS A resonance-approach, well known from technical practice (e.g., Anderson, 1967; Richardson, 1997) and previously adapted by Kaneko et al. (1981), was modified for the measurement of the dynamic characteristics of the vocal folds. Laryngeal vibrations were excited externally via a shaker placed anteriorly on the thyroid cartilage. The vibration response of the vocal folds was monitored laryngoscopically. Resonance frequencies (i.e., frequencies at which the vocal folds exhibit maximal amplitudes of vibration) and resonance modes of vibration (i.e., vibration patterns of the vocal folds at the resonance frequencies) were examined. The resonance frequencies and resonance modes can be seen as practical approximations of the eigenfrequencies and eigenmodes of the vocal folds. Fig. 1. Experimental set-up for the laryngoscopic examination of externally excited laryngeal vibrations. (More detailed information on the relationship between the eigenfrequencies/modes and resonance frequencies/modes can be found in literature on recorded on first channel of an FFT analyzer (Brüel dynamics of vibrating systems, e.g., Anderson, 1967). & Kjaer, type 2034 Dual Channel Signal Analyzer). Vibration force was registered by means of a force I.A. Experimental set-up transducer (Brüel & Kjaer, type 8200) which was The experimental set-up, shown in detail in Fig. 1, placed between the plexiglass cylinder and the vibrating consisted of three parts: 1) generation and monitoring element of the shaker. Signal from the force transducer of the vibration of the external shaker, 2) monitoring was amplified by a Brüel & Kjaer (type 2626) amplifier the force by which the shaker is pressed against the and recorded on second channel of the FFT analyzer. neck; and 3) laryngoscopic observation of the excited Signals from the generator, accelerometer and force vocal fold vibrations. transducer were used to obtain transfer functions of the excitation system. The transfer functions (force/ I.A.1. Excitation of the laryngeal vibrations generator as well as acceleration/generator) were Signal (sinusoidal and impulse, see section I.B for found to be essentially flat in the frequency range details) from a generator (HP type 3324A Synthesized 100– 400 Hz. Below 100 Hz, in the relevant range 50– Function Sweep Generator) was amplified by a VEB 100 Hz, the transfer functions monotonically decreased Metra Verstärker (type LV 103) and fed into a shaker with descending frequency. Maximum displacement (Brüel & Kjaer, type 4810). A specially designed amplitude of the shaker was observed at 50 Hz and plexiglass cylindrical head was firmly attached measured to be ca. 3 mm. (screwed) to a vibrating element of the shaker. This plexiglass head served as an electrically isolated contact I.A.2. Contact force measurement element which was placed on the neck of the subject. Body of the shaker was firmly attached onto a metal Acceleration of the cylindrical head was registered via rod (Fig. 1). The rod bent when the shaker was pressed an attached accelerometer (Brüel & Kjaer, type 4344). against the neck. The amount of bending was measured Signal from the accelerometer was amplified by means by means of a semiconductor strain gauge designed at of a vibration meter (Brüel & Kjaer, type 4511) and the Institute of Thermomechanics of the Academy of 62 Chapter 5: Resonance Properties of the Vocal Folds

Sciences of the Czech Republic (Vaněk and Cibulka, (Lambert Instruments) with a C-mount objective/ 1994). The strain gauge was powered from a stabilized adapter (ATMOS) were employed for video- power supply of 10 V (TESLA, type BS 525). Change kymography. Laryngeal image, registered by (either of voltage in the sensory circuit of the semiconductor standard or videokymographic) video camera attached strain gauge caused by the bending was monitored by to the endoscope, was presented simultaneously on means of a voltmeter (TESLA, type DU 20). The two video monitors (in Fig. 1, only one monitor is system was calibrated making it possible to convert depicted, for simplicity). The examiner used the first the measured voltage to the force applied to the shaker. monitor; the second monitor provided feedback to the examined subject. The images were recorded using I.A.3. Laryngoscopic observation of the excited laryngeal an s-VHS video tape recorder (Panasonic, model AG vibrations 7355). An audio signal was registered by means of an Two methods of monitoring the vocal-fold vibration electret microphone (Kay Elemetrics lapel were used: laryngostroboscopy and high-speed microphone, type 7175-6000) and recorded on audio videokymography. Laryngostroboscopy is a well-known track of the videotape. technique routinely used in laryngology and a more detailed description can be found elsewhere (e.g., I.B. Experimental procedure Hirano and Bless, 1993). Videokymography is a newly One of the authors (JGS, male, age 32, an amateur developed method for high-speed optical investigation jazz-singer) served as a subject for the study. The of vibrations (Švec and Schutte, 1996; Švec et al., phonation frequency of 110 Hz was chosen as a refe- 1997; 1999; Schutte et al., 1998). rence for the investigation. During the experiment In Videokymography (VKG) a modified video camera the subject placed the plexiglass cylindrical head of is used. The camera can function in two different the shaker anteriorly on the prominence of the thyroid modes, standard and high-speed. In the standard cartilage and pushed the neck against the shaker with mode, it works as a standard commercial video camera, a force of ca. 3–5 Newton (higher forces were monitoring the vibration of the vocal folds with a speed subjectively judged as uncomfortable). The shaker of 25 frames (respectively 50 interlaced fields) per was not firmly fixed to the neck, for safety reasons. second (CCIR/PAL standard was used here). An The subject at comfortable intensity in chest register example of a standard laryngoscopic image is shown reproduced the reference frequency, given by means in Fig. 2(a). of a tuning fork. Next, the endoscope was inserted In the high-speed mode the camera delivers images into the oral cavity and the subject repeated the from a single selected line with a speed of 7812.5 line phonation. After this, the subject took a breath images per second. These line images are put below and produced the Kaneko-maneuver: a short each other and together create a new, phonation which was interrupted while keeping the videokymographic image monitoring vibration of the vocal folds in the neutral phonatory position. selected part of the vocal folds in time [Fig. 2(b)]. Attempt was made to avoid any movement of the A mechanical switch enables to change between the larynx during the Kaneko maneuver. At this time, standard and high-speed modes instantly. Both the the external vibrations were delivered to the larynx. normal as well as the high-speed images are transmitted Three different approaches were used for in a standard TV format and can be recorded and investigating the externally excited laryngeal monitored using a standard video recorder and a TV- vibrations: compatible monitor. More detailed information on 1. Videostroboscopy: Sinusoidal excitation signal with videokymography can be found elsewhere (Švec and a constant frequency (50, 75, 100, 110, 125, 150, 175, Schutte, 1996; Švec et al., 1997; 1999). 200, 225, 250, 275, 300, 325, 350, 375 and 400 Hz) was Laryngoscopic set-up is shown in Fig. 1. For used and the laryngeal vibrations were monitored stroboscopy, the following equipment was used: Light videostroboscopically. source (Rhino-Laryngeal Stroboscope Kay Elemetrics, 2. Frequency sweep: Sinusoidal signal of constant model 9100), rigid endoscope (70° Kay Elemetrics, input power was delivered to the shaker and the type 9106), and 3CCD color camera (Panasonic GP- frequency was linearly increased. The vibration US502 with a Control Unit) with a C-mount 35mm amplitude of the shaker was dependent on the lens/adapter (Kay Elemetrics, model 9116). Xenon frequency of oscillation (see Appendix). Two frequency light source (Richard Wolf Auto LP/FLASH 5135), sweeps in the frequency range of 100–400 Hz and 50– Lupenlaryngoskop (90° Richard Wolf, model 4450.47), 200 Hz were used, each sweep of 5 s in duration. The and videokymographic CCD black and white camera measurement position was aimed at the middle of the Švec: On Vibration Properties of Human Vocal Folds 63 membranous part of the vocal folds, transversally to however, which appeared problematic for a detailed the glottis [Fig. 2(a)], using a standard mode of the analysis. The VKG data from this particular condition VKG camera. The measurement position was adjusted were thus not analyzed in detail and are not treated in manually by moving the endoscope to the desirable this study. The signals from the force transducer and position during the phonation preceding the Kaneko- accelerometer were used to obtain transfer functions maneuver. Before the start of the frequency sweep, of the excitation system (discussed in section II.A.1). the camera was switched into the high-speed mode and the position of the endoscope was held still during I.C. Analysis of the video data the sweep. After the end of the sweep, the VKG I.C.1. Frequency sweep: camera was switched back into the standard mode in Best VKG samples were selected from the order to confirm that the measurement position had videotape. The basic selection criteria were: a) cor- not changed during the VKG measurement. The rectly produced Kaneko-maneuver (see Appendix); measurement was repeated several times for each b) well focused image; c) clearly visible externally sweep. induced vibrations of the vocal folds with highest 3. Impulse excitation: A periodic rectangular impulse possible amplitude; d) VKG examination covering excitation signal of 1 ms duration was delivered from the whole frequency sweep (no interruptions of the the generator to the shaker. The vibration response of VKG image by the standard image); e) approximately the laryngeal tissues was observed by means of constant VKG measurement position during the videokymography. Vocal folds responded with damped sweep. A single sample for each frequency sweep was oscillations, their amplitude was found rather small, chosen for analysis. That sample was digitized and fed into a PC using a videoboard (Miro PCTV) and saved as an AVI file. A CorelScript program under CorelPhotoPaint 8 software was written in order to extract successive video fields from the AVI files and save them into a sequence of bitmaps (250 bitmap images per 1 sweep of 5 seconds in duration). Each 20 successive bitmaps then were concatenated (concatenating more than 20 bitmaps into a single image appeared unpractical for the software used), forming a “train” of video fields representing altogether the vocal fold vibration pattern within the time sequence of 400 ms, and saved as a new image [section of such an image with 3 concatenated video fields is given in Fig. 2(b)]. From these images, after an adjustment of an optimal contrast, amplitudes of the externally induced vocal fold vibration were extracted. Extremes of the displacements of the vocal folds and ventricular folds were read manually for every period [Fig. 2(d)] using a cursor in SigmaScan (Jandel Fig. 2. Standard and videokymographic (VKG) images of the larynx. (a) standard, laryngostroboscopic image of the vocal folds in neutral Scientific) software. Each value was represented by phonatory position. (b) high-speed VKG image at the position a pair of pixel values x,y (x pixel corresponding to the marked in (a). Chain of three successive VKG fields, each of 20 ms position of the vocal folds, y pixel corresponding to duration, is presented. Each field depicts ca. 18 ms of time, ca. 2 ms a specific time). The data were processed in SigmaPlot interruption between each two successive fields corresponds to a vertical blanking interval which is reserved for synchronization (Jandel Scientific) software. Here, the y pixel values purposes and does don contain any image data (CCIR/PAL video were converted to time values in milliseconds, standard). (c) sketch of the laryngeal image (a): vf – vocal fold, ve – amplitudes were calculated as a half of the difference ventricular fold, b – blood vessel on left ventricular fold, a – arytenoid between the displacement extremes for each vibration cartilage, ae – aryepiglottic folds, e – epiglottis. (d) sketch of the videokymographic image (b). Vibrating borders of the ventricular period, duration of periods was calculated and folds (dashed) and vocal folds (solid) are outlined. Dots on the converted to frequency values in Hz, best fit of the right vocal fold indicate the points used for measuring the amplitude measured frequency values was done using the known and frequency of the externally excited vibrations. Note that the parameters of the sweep (accuracy better than ±1 Hz), left and right sides are reversed in all the images (it reflects the situation seen by the examiner when facing the examined subject). and a graph of the frequency response was plotted. 64 Chapter 5: Resonance Properties of the Vocal Folds

Further on, the data were interpolated, smoothed via were identified at 171 and 241 Hz with bandwidths of the Kernel smoothing algorithm, and plotted. 44 and 45 Hz, respectively.

Resonance frequencies (Fr) and half-power (3 dB) Response of the right vocal fold is given in Fig. ∆ bandwidths ( Fr) were measured from the smoothed 3(b). It reveals two resonance peaks with central response curves. Fr were found as frequencies at which frequencies of 164 and 238 Hz and bandwidths of 37 ∆ the amplitude reached maximal value (Amax), Fr was and 41 Hz, respectively. An increase in the vibration measured as difference of two frequencies around Fr amplitude is evident also around 100 Hz, this resonance √ at which the amplitude was equal to Amax/ 2 falls, however, partially below the low frequency limit (Anderson, 1967; Herlufsen, 1984). of 100 Hz and therefore its central frequency and bandwidth cannot be identified. Smoothed frequency I.C.2. Videostroboscopy response functions of the vocal folds are set side by Videostroboscopic records representative of selec- side in Fig. 3(c). The measured resonance frequencies ted discrete frequencies were digitized and saved as (F ) and bandwidths (DFr) of both the vocal folds are AVI files. Four phases of a vibration cycle were selected summarizedr in Table I. (maximal and minimal displacements of the vocal folds, or other laryngeal structures, and two intermediate states) and composed into an image using Corel PhotoPaint 8 software. Sketches outlining borders of the laryngeal structures in their extreme positions were drawn carefully by hand using CorelDraw 8 software. No quantitative analysis of the stroboscopic images was done.

II. RESULTS II.A. 100 – 400 Hz frequency sweep Frequency response function of the left vocal fold for the 100 – 400 Hz sweep is shown in Fig. 3(a). Three resonance peaks with maxima at 114, 171 and 241 Hz are clearly pronounced here. The first resonance maximum is 4 Hz higher than the intended phonation frequency 110 Hz. Bandwidth of the first resonance peak was impossible to measure since the maximum was too close to the lower limit frequency of the sweep. The second and third resonance maxima

TABLE I. Resonance frequencies and half-power (3 dB) bandwidths of the vocal folds evaluated from 250 successive VKG fields representing one 100–400 Hz sweep.

Resonance Bandwidth

frequency Fr DFr (Hz) (Hz) Left vocal fold 1st resonance 114 unidentifiable 2nd resonance 171 44 Fig. 3. Frequency response functions of the vocal folds extracted 3rd resonance 241 45 from 250 successive VKG fields representing one 100–400 Hz sweep. Adjustment of the vocal folds corresponds to the phonation frequency of ca. 110 Hz (this reference frequency remains the Right vocal fold same for the whole study). (a) left vocal fold; (b) right vocal fold; st 1 resonance < 100 unidentifiable (c) smoothed curves for both vocal folds. Three resonance peaks 2nd resonance 164 37 centered near the frequencies of 110, 170 and 240 Hz are visible in 3rd resonance 238 41 the responses. Values above 350 Hz are not plotted since the amplitude of vibration was below the detection level. Švec: On Vibration Properties of Human Vocal Folds 65

II.B. 50 – 200 Hz frequency sweep The second resonance peak in both the vocal folds In order to find out the dynamic characteristics of observed in Fig. 4 corresponds to the first resonance the vocal folds below 100 Hz, the data from the 50– peak found in Fig. 3 in the previously described 100 – 200 Hz frequency sweep were analyzed. Smoothed 400 Hz sweep. The resonance frequencies from these frequency response functions of both the vocal folds two measurements are close, but not identical (the for this sweep are shown in Fig. 4. Large left-right observed difference in the left vocal fold is 10 Hz), asymmetry is evident in the graph. The left vocal fold which may suggest that the vocal folds were adjusted exhibits two distinct resonance peaks around the slightly differently during the two measurements. central frequencies of 77 and 104 Hz. The right vocal Besides the vocal folds also ventricular folds clearly fold shows a weak maximum at 58 Hz and a strong responded to the external excitation (Fig. 5). Maximal resonance peak with two local maxima at 92 and 100 vibration amplitudes of the ventricular folds were more Hz. Bandwidths of these resonance peaks were not than twice as large as those of the vocal folds within measured due to their nontrivial shape. A local this frequency range. Maxima were identified at 67 minimum, suggesting an antiresonance, is found in and 72 Hz for the left and right ventricular fold, the right vocal fold at the frequency of 75 Hz. respectively. Figure 5 reveals local maxima also at 80, 105 and 125 Hz (left) and 94, 108 and 129 Hz (right); these resonance peaks are relatively weak, however. The resonance frequencies of the vocal folds and ventricular folds identified from the 50 –200 sweep are summarized in Table II.

TABLE II. Resonance frequencies of the vocal folds and ventricular folds evaluated from 250 successive VKG fields representing one 50–200 Hz sweep.

Resonance Note

frequency Fr (Hz) Left vocal fold Fig. 4. Frequency response functions of the vocal folds extracted lower resonance 77 — from 250 successive VKG fields representing one 50-200 Hz sweep (after Kernel smoothing). Maximum response of the vocal folds is higher resonance 104 asymmetric peak located around 100 Hz, below this frequency there are large left- right differences. Amplitude of the shaker was reduced here with Right vocal fold respect to the measurement shown in Fig. 3. lower resonance 62 weak higher resonance 92, 100 double peak

Left ventricular fold 67 asymmetric peak

Right ventricular fold 72 asymmetric peak

II.C. Laryngostroboscopy Laryngostroboscopic investigation was used to find out the vibration shapes of the vocal folds during the external excitation at distinct frequencies in order to distinguish the resonance modes of vibration. A laryngostroboscopic image of the studied vocal folds in the neutral phonatory position is presented in Fig. 2(a); its sketch is given in Fig. 2(c). The larynx appeared generally normal, it differed Fig. 5. Frequency response functions of the ventricular folds extracted from the same images as used in Fig. 4 (after Kernel slightly from an ideal laryngeal outlook in two features: smoothing). Maximal responses of the ventricular folds appear 1) there was a slight left-right asymmetry, especially in around 70 Hz. Responses of the vocal folds (identical to those in the position of the arytenoid cartilages [this finding Fig. 4) are also shown, for comparison. 66 Chapter 5: Resonance Properties of the Vocal Folds may not be considered unusual, however, since some advantage since it eliminated the collision between degree of asymmetry is observed practically in all the vocal folds that would otherwise perturb their larynges (Hirano et al., 1989; Lindestad, 1997)]; 2) oscillations. Sequences of laryngostroboscopic images the vocal folds were slightly bowed, thus the glottis at frequencies 50, 75, 100, 110, 175 and 250 Hz are remained slightly open in the neutral phonatory presented in Figures 6 and 8, sketches extracting the position. For the purpose of this study, the bowing oscillation of the laryngeal tissues from these images was not considered as an impediment but rather an are given in Figures 7 and 9.

Fig. 6. Series of laryngostroboscopic images of the externally excited laryngeal Fig. 7. Sketches showing positions of the laryngeal vibrations at the frequencies of 50, 75 and 100 Hz. Five successive phases of the structures at two opposite phases of the vibratory vibration cycle are shown; images A and E, G and K, and M and Q represent cycle at 50, 75 and 100 Hz (solid versus dashed lines, the same phase at the beginning and the end of the stroboscopic cycle. extracted from images A and C, G and I, M and O in Videokymographic images at the bottom (F, L, R) show vibration of the Fig. 6, respectively). Large amplitudes of vibration of laryngeal structures at the positions marked in the images E, K and Q. the aryepiglottic folds and arytenoid cartilages are Oscillations of the aryepiglottic folds and arytenoid cartillages are dominant at evident at 50 Hz (top), these amplitudes successively 50 (A-E) and 75 Hz (G-K), the VKG image L reveals also large oscillations of decrease with increasing the external driving the ventricular folds at 75 Hz. Opening-closing response of the vocal folds is frequency to 75 (middle) and 100 Hz (bottom). Large apparent at 100 Hz (M-O). (See the sketches in Fig. 7). amplitude of the left ventricular fold can be observed at 75 Hz. An evident response of the vocal folds, an opening-closing motion, can be seen at 100 Hz. Švec: On Vibration Properties of Human Vocal Folds 67

Excitation at 50 Hz: at this frequency, large 110 Hz 175 Hz 250 Hz oscillations of the laryngeal collar, especially the aryepiglottic folds and arytenoid cartilages, were visually dominant in the stroboscopic view [Fig. 6(A- F), Fig. 7 top]. Vocal folds oscillated as a unit with other laryngeal structures. Left-right and anterior- posterior phase differences in oscillation were visible across the laryngeal structures; no analysis of these phase shifts was done, however. Excitation at 75 Hz: Oscillations of the arytenoid and aryepiglottic folds were dominant at this frequency, their amplitudes were, however, smaller compared to the frequency of 50 Hz [Fig. 6(G-L), Fig. 7 middle]. Ventricular folds (or, more accurately, the spatial distance between the medial borders of the ventricular folds) exhibited large vibrations [this is partially obscured in the stroboscopic images; VKG image in Fig. 6(L) reveals the large amplitude of the ventricular folds more clearly]. Oscillation of the left vocal fold was noticed in Fig. 6(L), its vibration amplitude was small with respect to the amplitudes of the ventricular folds, arytenoid cartilages and aryepiglottic folds. In the stroboscopic view [Fig. 6(G-K)], the right anterior part of the larynx appeared slightly squeezed, presumably due to slightly asymmetrical placement of the shaker on the neck. Excitation at 100 Hz: at this frequency (only 10 Hz lower than the reference phonation frequency) the vocal folds responded by a clear opening-closing movement [Fig. 6(M-R), Fig. 7 bottom]. Amplitudes of vibration of the arytenoid cartilages, aryepiglottic Fig. 8. Series of laryngostroboscopic images of the externally excited folds and ventricular folds were smaller compared to vocal-fold vibrations at the frequencies of 110, 175 and 250 Hz. The stroboscopic and VKG images are selected and organized the excitation at 75 Hz. analogously to Fig. 6. (See the sketches in Fig. 9 for more details). Excitation at 110 Hz: excitation frequency matched the reference phonation frequency here. A clear opening-closing movement of the vocal folds was dominant in the larynx [Fig. 8(A-F), Fig. 9 left]. Oscillations of other laryngeal structures were of relatively small amplitude and are not shown here. Excitation at 175 Hz: here, the external frequency was very close to the second resonance frequency of the vocal folds (in accordance with Fig. 3). The vocal folds responded with lateral-medial oscillations encompassing two half-wavelengths along the glottal length – anterior and posterior parts of the glottis oscillated with opposite phases [Fig. 8(G-L), Fig. 9 Fig. 9. Sketches illustrating the vibration shapes of the vocal folds at two opposite phases of the vibratory cycle at 110, 175 and 250 Hz middle]. (solid versus dashed lines, extracted from images A and C, G and I, Excitation at 250 Hz: here, the external frequency and M and O in Fig. 8, respectively). These vibration shapes was close to the third resonance frequency of the represent the resonance mode shapes associated with the first vocal folds (in accordance with Fig. 3). Despite of three resonance frequencies of the vocal folds. 110 Hz: opening- closing (x-1) mode; 175 Hz: anterior and posterior halves of the small amplitude of the vibration it was possible to glottis oscillate with opposite phases (x-2 mode); 250 Hz: middle identify response in the vocal folds showing lateral- third of the glottis oscillates at an opposite phase to the anterior medial oscillations encompassing three half- and posterior thirds (x-3 mode). 68 Chapter 5: Resonance Properties of the Vocal Folds wavelengths along the glottal length, the middle part their combination) is responsible for the first resonance of the glottis oscillated in an opposite phase to the peak. The recent analysis of Berry (in review) suggests anterior and posterior parts [Fig. 8(M-Q), Fig. 9 right]. that all the modes from the x-1 class (x-10, x-11, x-12, etc.) cluster into a joint resonance peak which makes III. DISCUSSION them practically undistinguishable in the laryngoscopic The results bring an encouraging message: view. This result would correspond with our difficulties principally, it is possible to use laryngoscopy for with distinguishing these modes. obtaining more detailed information on dynamic Certain discrepancies were found in our data characteristics of the vocal folds. Three distinct between the 50 – 200 Hz and 100 – 400 Hz sweeps. resonance frequencies of the vocal folds were found The responses of the vocal folds were expected to be around 110, 170 and 240 Hz. The first resonance similar in the overlapping range 100 – 200 Hz. frequency around 110 Hz corresponded to the Comparison of Fig. 3(c) and Fig. 4 reveals clear frequency of phonation. The resonance frequencies differences in this range, however: the first resonance were found to be associated with different modes of frequency Fr1 in the 100 – 400 Hz sweep is slightly vibration of the vocal folds. Fig. 9 reveals the associated higher than the corresponding resonance frequency resonance mode shapes as seen in the laryngoscopic measured in the 50 – 200 Hz sweep (114 vs. 104 Hz, view; these three mode shapes can be designated as respectively, was measured on the left focal fold). modes x-1, x-2 and x-3, respectively (1, 2, 3 meaning This suggests that the vocal folds might have been the number of the half-wavelengths along the tuned slightly differently in these two measurements. longitudinal axis of the vocal folds). Another and more serious discrepancy is that the The resonance frequencies show an interesting resonance peak around 170 Hz, which is clearly relationship: it can be seen from the results in Table I, pronounced in both the vocal folds in the 100 – 400 particularly in the case of the left vocal fold, that the Hz response curve, is not present in the 50 – 200 Hz relationship of the resonance frequencies Fr1 : Fr2 response of the vocal folds. This discrepancy might be

(114 : 171 Hz) is exactly 2:3, the relationship Fr1 : Fr2 : Fr3 attributed to at least two factors. First, the amplitude (114 : 171 : 241 Hz) is close to 2:3:4. Theoretically, if of the vibrations of the shaker, which was reduced in all the modes associated with these resonance the 50 – 200 Hz sweep, might have been too small to frequencies would be excited simultaneously during excite the vibration of the vocal folds at this resonance phonation, a complex vocal-fold vibration with frequency to a laryngoscopically detectable level. a resulting subharmonic frequency of Fr1/2 (57 Hz) Second, and even more plausible origin of this would be produced. This finding might be related to discrepancy might be due to slightly different an F0/2 subharmonic phonation which was found in measurement position used for the two VKG the same subject when phonating with slightly abducted investigations. Whereas in the 50 – 200 Hz sweep the vocal folds at high airflow volume velocities. The VKG measurement position was close to the middle complex vibration pattern of the vocal folds typical of the glottis (Fig. 6, images E,K,Q), which is the for this phonation was described in detail in our nodal point of the x-2 mode at which the amplitude is previous study (Švec et al., 1996). The 2:3:4 minimal, in the 100 – 400 Hz sweep the measurement relationship is, however, suspected to be not a general line was placed in a more anterior part of the glottis but rather specific feature of the vocal folds (Fig. 8, images E,K,Q) where the amplitude of the x-2 investigated here, since the phonatory maneuver of mode is maximal. Such sensitivity of the results to the

Švec et al. (1996) was found to lead to the F0/2 VKG measurement position is one of the pitfalls of subharmonic phonation not in every subject. the VKG method used here. A more complete list of The laryngoscopic findings do not support the the potential complications and pitfalls is given in the hypothesis of Ishizaka (1988) that the x-11 mode is Appendix. related to the second resonance frequency of the vocal Not only the vocal folds but also other laryngeal folds; it was rather the x-2 mode which was found to structures apparently responded to the vibrations play the role here. The out-of-phase oscillations of applied externally on the neck. Below 100 Hz, the upper and lower margins of the vocal folds, typical amplitude of vibration of the vocal folds was much of the x-11 mode, were not distinguished in the present smaller than that of the ventricular folds (their study since the lower margin remained hidden in the resonance frequency was identified to be close to 70 laryngoscopic view and it was impossible to detect its Hz, see Table II) as well as the aryepiglottic folds and movement. For the same reason, it was impossible to arytenoid cartilages (their resonance frequency is clearly specify whether the x-10 or the x-11 mode (or suspected to be close to 50 Hz in this subject). Different Švec: On Vibration Properties of Human Vocal Folds 69 parts of the larynx thus appear to be tuned to different APPENDIX: GENERAL COMPLICATIONS AND resonance frequencies. The resonance and PITFALLS OF THE METHOD PRESENTED antiresonance peaks of the vocal folds found below 100 Hz (Fig. 4) are suspected to have the origin in an A. Vocal folds and the Kaneko-maneuver interaction of the vocal-fold vibration with the vibration 1) Vocal-fold tuning: there is no control of the vocal- of the adjacent laryngeal structures. The large left- fold tuning in the neutral phonatory position, thus it is right asymmetry in the vocal fold response below 100 not certain that the tension of the vocal folds remains Hz (Fig. 4) is assumed to be related to the clear the same as compared to the actual phonation. The asymmetry of the laryngeal structures shown in Fig. difference in the tension may result in a change of the 2(a). dynamic characteristics. The accuracy of the Kaneko- In future studies it is important to investigate the maneuver in living subjects remains to be specified in dynamic characteristics of the vocal folds at various this respect. frequencies of phonation and in more subjects. More 2) Degree of adduction: investigated subject might detailed information on dynamic characteristics of tend either to abduct (open) or to hyperadduct (press the other laryngeal structures, like, e.g., the ventricular together) the vocal folds during the neutral phonatory folds, could also be helpful since these structures position while holding the breath. In order to avoid contribute to phonation in certain singing styles (Fuks this tendency, laryngoscopic view was monitored and et al., 1998; Lindestad and Södersten, 1999) or in provided as a feedback to the experimental subject as patients with voice disorders (Kruse, 1981; von well as to the examiner. The Kaneko maneuver and Doersten et al., 1992; Schutte et al., 1998; Švec et al., the neutral phonatory position were judged correct if 1997; 1999). For a more extensive analysis, however, the vocal folds were kept essentially in the same it is desirable to employ automated or semi-automated position as they were during the preceding phonation. image detection (Wittenberg, 1997; 1998; Saadah et 3) Airflow: even a small amount of glottal flow al., 1998; Larsson et al., 1999) instead of manual might influence behavior of the vocal folds, thus the analysis of the images which is exceedingly time- glottal flow shall be avoided when the vocal folds are consuming. Certain other questions remain to be in the neutral phonatory position. Small airflow answered, e.g., whether the direction of the frequency velocities are, however, difficult to perceive by the sweep does not influence the observed resonance examined subject when the shaker vibrations are properties. In general, however, the method presented applied onto the neck. In our case, the far-from- here appears useful and promising for studying the sinusoidal vibration pattern of the vocal folds seen in dynamic characteristics of the larynx. the videokymogram R in Fig. 6 with an indication of a shear movement of the vocal folds and the occurrence FOOTNOTE: of mucosal waves leads us to suspect that some glottal In the x-ij notation, “x” designates oscillations in the flow might have distorted the externally (sinusoidally) lateral-medial direction and the i,j indices give number of excited vibrations at that particular moment during oscillatory half-wavelengths occurring along the horizontal the VKG examination. and vertical dimensions of the vocal folds (i.e., length and thickness), respectively. For a more detailed description and examples see, e.g., Titze and Strong (1975); Titze (1994); B. Laryngoscopy Berry et al. (1994), Berry and Titze (1996), Berry (in review). An important aspect is the constant measurement position during VKG examination. The difference in the VKG measurement position is suspected to be the ACKNOWLEDGMENTS main origin of the discrepancies found between the The paper was presented to the 2nd International two sweeps. A full-image high-speed video recording Conference on Voice Physiology and Biomechanics, system would be an alternative which would allow to March 12-14, 1999, Berlin, Germany. The authors are select the proper measurement position after the grateful to the Sound Studio of the Academy of examination as well as to correct the measuring Performing Arts in Prague for providing us with a part position in case of some unpredictable motion (of the of the equipment needed for the experiment. The endoscope or of the examined subject) during the research has been supported by the Grant Agency of examination (Wittenberg et al., 1995; Wittenberg, the Czech Republic (GA ČR), project no. 109/98/ 1998; Larsson et al., 1999). K019. 70 Chapter 5: Resonance Properties of the Vocal Folds

Another problem is that the laryngoscopic view modal properties of the vocal fold tissues],” in 15th does not allow to reliably identify vertical movements Conference COMPUTATIONAL MECHANICS ’99, of the vocal folds and distinguish, e.g., the x-10 versus October 18–20, 1999, Nečtiny, Czech Republic edited by J. x-11 mode, or the theoretically described z-modes of Křen. (University of West Bohemia, Pilsen) pp. 39–46. von Doersten, P. G., Izdebski, K., Ross, J. C., Cruz, R. M. the vocal folds (Berry et al., 1994; Berry and Titze, (1992). “Ventricular dysphonia: a profile of 40 cases,” 1996). Also, a good laryngoscopic view of the larynx Laryngoscope 102: 1296–301. and tolerance of the endoscope might be problematic Fletcher, N. H. (1996). “Nonlinearity, complexity, and control in some subjects. in vocal systems.” in Vocal fold physiology: controlling complexity and chaos edited by P. J. Davis and N. H. C. Shaker Fletcher (Singular Publishing Group, San Diego, CA) For safety reasons, it is not recommended to fix the pp. 3–16. shaker to the living larynx. Due to this, the contact Fuks, L., Hammarberg, B., and Sundberg, J. (1998). “A self- force as well as the position of the shaker on the neck sustained vocal-ventricular phonation mode: acoustical, aerodynamic and glottographic evidences,” TMH–QPSR may vary slightly (laterally or vertically) which could 3/1998, 49–59. alter the excitation force acting on the vocal folds. Fukuda, H., Muta, H., Kanou, S., Takayama, E., Fujioka, T., The variation of the contact force was suppressed Kawaida, M., Tatehara, T., and Saito, S. (1987). “Response here by monitoring its value and using it as a feedback. of vocal folds to externally induced vibrations: basic study The shaker placement is assumed not to be critical for and its clinical application,” in Laryngeal function in investigating the dynamic characteristics of the vocal phonation and respiration edited by T. Baer, C. Sasaki, folds: Kaneko et al. (1981) reported no significant and K. S. Harris (A College-Hill Press/Little, Brown and differences in the resonance properties of the vocal Company, Boston/Toronto/San Diego) pp. 366–377. folds when the position of the shaker on the larynx Fukuda, H. (1993). “Fundamental study on vocal fold vibration and its clinical application,” Ann. Bull. RILP was varied. (Tokyo) No. 27, 89–102. At constant excitation force, the amplitude of Herlufsen, H. (1984). “Dual channel FFT analysis (Part vibrations of the shaker is inversely proportional to II),” Brüel & Kjaer Technical Review No. 2. the second power of frequency. This leads to excessive Hirano, M., and Bless, D. M. (1993). Videostroboscopic vibration amplitudes at low frequencies and small examination of the larynx (Singular Publishing Group, displacement amplitudes at high frequencies. San Diego, California). Therefore two different sweeps were used in the Hirano, M., Yukizano, K., Kurita, S., and Hibi, S. (1989). present study. Highest possible excitation force was “Asymmetry of the laryngeal framework: a morphologic used for the 100–400 Hz sweep in order to achieve study of the cadaver larynges,” Ann. Otol. Rhinol. Laryngol. 98, 135–140. maximal oscillatory response in the laryngeal tissues. Ishizaka, K. (1988). “Significance of Kaneko’s measurement For the 50–200 Hz sweep, the input power of the of natural frequencies of the vocal folds,” in Vocal fold shaker was reduced; otherwise the excessive shaker physiology, vol. 2: Voice production mechanisms and amplitudes at low frequencies (excursions of ca. ±3 mm functions edited by O. Fujimura (Raven Press, New York), at 50 Hz) caused uncomfortable sensations in the pp. 181–190. subject. It appears desirable to compensate for this Ishizaka, K., and Flanagan, J. L. (1972). “Synthesis of voiced phenomenon in future studies. sounds from a two-mass model of the vocal cords,” Bell. Sys. Tech. J. 51, 1233–1268. Jiang, J. J., Diaz, C. E., and Hanson, D. G (1998). „Finite REFERENCES element modeling of vocal fold vibration in normal Anderson, R. A. (1967). Fundamentals of vibrations. (The phonation and hyperfunctional dysphonia – implications Macmillan Company, New York). for the pathogenesis of vocal nodules,“ Ann. Otol. Rhinol. Berry, D. A., Herzel, H., Titze, I. R., and Krischer, K. Laryngol. 107, 603–610. (1994). “Interpretation of biomechanical simulations of Kaneko, T., Uchida, K., Suzuki, H., Komatsu, K., Kanesaka, normal and chaotic vocal fold oscillation with empirical T., Kobayashi, N., and Naito, J. (1981). “Mechanical eigenfunctions,” J. Acoust. Soc. Am. 95, 3595–3604. properties of the vocal fold: measurement in vivo,” in Berry, D. A., and Titze, I. R. (1996). “Normal modes in Vocal fold physiology edited by K. N. Stevens and M. a continuum model of vocal fold tissues,” J. Acoust. Soc. Hirano (University of Tokyo Press, Tokyo), pp. 365–376. Am. 100, 3345–3354. Kaneko, T., Komatsu, K., Suzuki, H., Kanesaka, T., Masuda, Berry, D. A. (in review). “Mechanism of non-modal T., Numata, T., and Naito, J. (1983). “Mechanical phonation,” J. Phonetics. properties of the human vocal fold – resonance Dedouch, K., Vampola, T., and Švec J. (1999). “Analýza characteristics in living humans and in excised larynges,” vlivu délky kmitající části hlasivky na změnu modálních in Vocal fold physiology: Biomechanics, acoustics and vlastností hlasivky. [Influence of the length change on phonatory control edited by I. R. Titze and R. C. Scherer Švec: On Vibration Properties of Human Vocal Folds 71

(The Denver Center for the Performing Arts, Denver, Švec, J. G., Schutte, H. K., and Miller, D. G. (1996). CO), pp. 304–317. “A subharmonic vibratory pattern in normal vocal folds,” Kaneko, T., Masuda, T., Shimada, A., Suzuki, H., Hayasaki, J. Speech Hear. Res. 39, 135–143. K., and Komatsu, K. (1987). “Resonance characteristics Švec, J. G., Schutte, H. K., and Šram F. (1997). Introduction of the human vocal fold in vivo and in vitro by an impulse to videokymography (Video tape). (Medical Healthcom, excitation,” in Laryngeal function in phonation and Prague). respiration edited by T. Baer, C. Sasaki, and K. S. Harris Švec, J. G., Šram, F., and Schutte, H. K. (1999). “Video- (A College-Hill Press/Little, Brown and Company, kymografie: nová vysokofrekvenční metoda vyšetřování Boston/Toronto/San Diego), pp. 349–365. kmitů hlasivek [Videokymography: a new high-speed Kruse, E. (1981). “Der Mechanismus der Taschenfalten- method for the examination of vocal-fold vibrations],” stimme. Eine kritische alternative Erwiderung auf die Otorinolaryngol. (Prague) 48, 155–162. Vorstellungen Réthis,” Folia Phoniatr. 33, 294–313. Tanabe, M., Isshiki, N., and Sawada, M. (1979). “Damping Larsson, H., Hertegård, S., Lindestad, P.–Å., and ratio of the vocal cord,” Folia Phoniatr. 31, 27–34. Hammarberg, B. (1999). “Vocal fold vibrations: high- Titze, I. R. (1976). “On the mechanics of vocal-fold speed video imaging, kymography and acoustic analysis,” vibration,” J. Acoust. Soc. Am. 60, 1366–1380. Karolinska Institute, Huddinge University Hospital Titze, I. R. (1988). “The physics of small–amplitude Phoniatric and Logopedic Progress Report 11, 7–16. oscillation of the vocal folds,” J. Acoust. Soc. Am. 83, Lindestad, P. –Å. (1997). Laryngeal asymmetries in normals, 1536–1552. preliminary results. Poster presented at the Pan European Titze, I. R. (1994). Principles of voice production (Prentice- Voice Conference PEVOC II, Regensburg, Germany, Hall, Englewood Cliffs, NJ). August 29–31, 1997. Titze, I. R., and Strong, W. (1975). “Normal modes in vocal Lindestad, P. –Å., and Södersten, M. (1999). “Voice source fold tissues,” J. Acoust. Soc. Am. 57, 736–744. characteristics in Mongolian “throat singing” studied Vaněk, F., and Cibulka, J. (1994). “Křemíkové tenzometrické with high speed imaging technique, acoustic spectra and čidlo síly. [Silicon force sensor],” in Proceedings of the inverse filtering,” Karolinska Institute, Huddinge Colloquium Dynamics of Machines ’94, Prague, April 11– University Hospital Phoniatric and Logopedic Progress 13, 1994 (Institute of Thermomechanics of the Academy Report 11, 17–26. of Sciences of the Czech Republic, Prague), pp. 97–100. Richardson, M. H. (1997). “Is it a mode shape, or an Wittenberg, T., Moser, M., Tigges, M., and Eysholdt, U. operating deflection shape?” Sound and Vibration 31, (1995). “Recording, processing, and analysis of digital 54–61. high-speed sequences in glottography,” Machine Vision Saadah, A. K., Galatsanos, N. P., Bless, D., and Ramos, C. and Applications 8, 399–404. A. (1998). “Deformation analysis of the vocal folds from Wittenberg, T. (1997). “Automatic motion extraction from videostroboscopic image sequences of the larynx,” J. laryngeal kymograms,” in Advances in Quantitative Acoust. Soc. Am., 103, 3627–3641. Laryngoscopy. Proceedings of the 2nd ‚Round Table‘ Schutte, H. K., Švec, J. G., and Šram, F. (1998). “First Advances in Quantitative Laryngoscopy using Motion–, results of clinical application of videokymography,” Image– and Signal Analysis, Erlangen 1997 edited by T. Laryngoscope 108, 1206–1210. Wittenberg, P. Mergell, M. Tigges, and U. Eysholdt Stevens, K. N. (1977). “Physics of laryngeal behaviour and (Abteilung Phoniatrie, Universitäts-HNO-Klinik Göttin- larynx modes,” Phonetica, 34, 264–279. gen, Germany), pp. 21–28. Švec, J. G., and Schutte, H. K. (1996). “Videokymography: Wittenberg, T. (1998). Wissenbasierte Bewegungsanalyse high-speed line scanning of vocal fold vibration,” J. Voice von Stimmlippenschwingungen anhand digitaler Hoch- 10, 201–205. geschwindigkeitsaufnahmen. Doctoral dissertation (Shaker Verlag, Aachen, Germany). 72 Chapter 5: Resonance Properties of the Vocal Folds SECTION II: Development and Application of Videokymography Chapter 6: Videokymography: High-Speed Line Scanning of Vocal Fold Vibration by J. G. Švec & H. K. Schutte Journal of Voice, 10(2): 201–205 (1996)

CHAPTER 6

Videokymography: High-Speed Line Scanning of Vocal Fold Vibration

Švec J. G., Schutte H. K.

Švec: On Vibration Properties of Human Vocal Folds 75 76 Chapter 6: Videokymography: High-Speed Line Scanning Švec: On Vibration Properties of Human Vocal Folds 77 78 Chapter 6: Videokymography: High-Speed Line Scanning Švec: On Vibration Properties of Human Vocal Folds 79 80 Chapter 6: Videokymography: High-Speed Line Scanning Chapter 7: First Results of Clinical Application of Videokymography by H. K. Schutte, J. G. Švec & F. Šram Laryngoscope, 108: 1206–1210 (1998)

CHAPTER 7

First Results of Clinical Application of Videokymography

Schutte H. K., Švec J. G., Šram F.

Švec: On Vibration Properties of Human Vocal Folds 83 84 Chapter 7: First Results of Clinical Application of Videokymography Švec: On Vibration Properties of Human Vocal Folds 85 86 Chapter 7: First Results of Clinical Application of Videokymography Švec: On Vibration Properties of Human Vocal Folds 87 88 Chapter 7: First Results of Clinical Application of Videokymography Chapter 8: Variability of Vibration of Normal Vocal Folds as Seen in Videokymography by J. G. Švec, H. K. Schutte & F. Šram In: Dejonckere PH, Peters HFM (Eds.): Communication and Its Disorders: A Science In Progress. Proceedings 24th Congress International Association of Logopedics and Phoniatrics, Amsterdam, the Netherlands, August, 23–27, 1998. Vol. I. International Association of Logopedics and Phoniatrics: 122–125 (1999) CHAPTER 8

Variability of Vibration of Normal Vocal Folds as Seen in Videokymography

Švec J. G., Schutte H. K., Šram F.

In: Dejonckere PH, Peters HFM (Eds.): Communication and Its Disorders: A Science In Progress. Proceedings 24th Congress International Association of Logopedics and Phoniatrics, Amsterdam, the Netherlands, August, 23–27, 1998. Vol. I. International Association of Logopedics and Phoniatrics: pp. 122–125 (1999). ISBN: 90 5710 071 1 Reprinted with permission

Švec: On Vibration Properties of Human Vocal Folds 91

Variability of Vibration of Normal Vocal Folds as Seen in Videokymography

Jan G. Švec, *Harm K. Schutte, František Šram

Center for Communication Disorders, Medical Healthcom, Ltd., Department of Phoniatrics and Audiology, Institute for Postgraduate Medical Education, Prague, the Czech Republic

and

* Groningen Voice Research Lab, Department of Biomedical Technology, Faculty of Medical Sciences, University of Groningen, the Netherlands

ABSTRACT Videokymography (VKG) is an easy, powerful and cost-friendly method to observe the variability of the vocal fold vibration. It is important to realize, however, that the measuring position is an essential factor here. It should be checked at which position along glottal length the measurement is taken as well as whether the glottal axis is perpendicular to the measuring line. The vocal fold vibration changes with loudness, pitch, type of phonation, voice register. In some cases, the vibration of normal vocal folds may become irregular (such as in vocal fry, breathy voice, or coughing). As normal larynges are rarely ideally symmetric, one can often observe some degree of phase delay of one vocal fold with respect to the second one, under extreme conditions (as, e.g., high pitch or intensity) the vibrations of the two vocal folds can also get desynchronized. Understanding better the vibration of normal vocal fold should improve our ability to recognize and distinguish various abnormalities and pathologies.

INTRODUCTION Such features as amplitudes of vibration, asymmetry Videokymography (VKG) is a new high-speed in phase and amplitude, vertical phase differences or imaging technique for investigation of vibration mucosal waves are nicely visible in VKG [1–3]. developed especially for examination of vocal fold Similarly as in classical high-speed recordings or vibrations. The system uses a modified B&W video stroboscopy, various quotients, such as, e.g., open camera which is able to work in two modes – normal quotient (OQ: defined as the duration of the open (50 or 60 images/s in CCIR or NTSC norm, phase divided by the duration of the glottal cycle) respectively) and high-speed (nearly 8 000 images/s). [4–6] can be utilized to describe the variability of the In the normal mode the system functions as a normal observed vibration. The technique is suitable for commercial video camera. In the videokymographic examination of all kinds of vocal fold vibrations, including mode the camera selects just a single horizontal line rough, breathy, hoarse or diplophonic which makes it from the whole image and monitors it with a high promising for clinical practice (see [7, 8]). In order to speed. A new, videokymographic image is composed explore the VKG technique for clinical purposes, by putting the successive high-speed line images below however, it is useful to know the variability of vibration each other. This image monitors the vibration of the in normal vocal folds as shown by this method. selected part of the vocal folds in time. Both the The present study is retrospective: the data from normal as well as high-speed images can be recorded normal subjects were gathered during numerous on a standard videorecorder which makes this observations and experiments carried out in the technique cost-friendly. A more detailed explanation Groningen Voice Research Lab and Center for Commu- of the principle of the VKG method can be found nication Disorders, Medical Healthcom in Prague since elsewhere [1–3]. the development of the VKG method in 1994. 92 Chapter 8: Normal Variability in Videokymography

FACTORS RELATED TO VARIABILITY OF THE VIDEOKYMOGRAPHIC VIBRATORY PATTERN OF THE VOCAL FOLDS Generally two basic factors should be taken into account when considering the variability of the VKG vibratory pattern: the measuring position and the variability of the vocal fold vibration itself.

A) Measuring position A.1) Position of the measuring line along glottal length The vibratory patterns of the anterior, middle and posterior part of the vocal folds are generally different. There are differences in amplitudes (usually greatest in the middle) as well as in the duration of the various Fig. 1. Vibration of the middle part of normal female vocal folds at phases of the cycle (closed, open, opening, closing) different levels of loudness (from left to right: soft, middle, loud). The fundamental frequency (F ) was kept constant (ca. 240 Hz). which lead to different values of, e.g., open or speed 0 The figure shows that with increasing loudness the amplitudes quotient [7, 9]. increase, the closed phase prolongs (OQ = 0.87, 0.65, 0.57, from left to right, respectively), the closing phase shortens, and the A.2) Rotation angle of the measuring line with respect to vertical phase differences become more prominent. A slight right- glottal axis left phase difference is present in all cases. (Total time displayed, ca. 18.4 ms, in all cases). The vocal fold axis may sometimes appear somewhat rotated. The oblique position of the glottal axis with respect to the measuring line is not advantageous since it may cause artifacts in the measured vibratory pattern (e.g., illusory asymmetry). In order to avoid this, the measuring line should be perpendicular to the glottal axis.

B) Change of voice quality B.1) Loudness, pitch, type of phonation, register There is large variability in the phonatory adjustments which results in a considerable variability of the vocal fold vibration. Together with aerodynamic adjustments, various laryngeal adjustments lead to different loudness (SPL), pitch (frequency), as well as type of phonation (breathy, normal, pressed, etc.). Fig. 2. Vibratory pattern of the middle part of normal male vocal

Videokymography enables an easy observation of folds in chest and falsetto registers. Left: chest register with F0 = changes in the vibratory pattern related to these ca. 180 Hz, large amplitudes, approximately equal closed and open factors. Figure 1 demonstrates the change of loudness phases (CQ = 0.5), and large vertical phase differences. Right: falsetto register with F0 = ca. 290 Hz, lack of a closed phase as reflected in VKG. (OQ = 1), smaller amplitudes, and invisible vertical phase One of the most controversial subjects related to differences. (Total time displayed, ca. 18.4 ms, in both cases). normal voice are vocal registers. Fig. 2 shows vibratory pattern of the chest and falsetto registers. The irregularity occurs, for instance during so called creaky differences among these three types of phonation are voice. Fig. 3 (left) shows an example of creaky voice clearly visible here. There is an effort to explore VKG with a subharmonic vibratory pattern (note the double for a more detailed description of the differences opening of the vocal folds). Within this type of between the registers. The method appears particu- phonation the vocal fold vibration is often unstable larly useful in observing transitions and sudden changes and may exhibit sudden changes, like octave jumps. between the adjacent registers. In contrast to the creaky voice in which the vocal folds are well adducted (note the long closed phases) B.2) Irregularities another example of irregularity appears, for instance, Normal vocal folds may also vibrate irregularly and when a lot of air is suddenly exhaled through rather imitate pathologic-like phonations (Fig. 3). The abducted vocal folds. In this case a breathy hoarse Švec: On Vibration Properties of Human Vocal Folds 93 voice is produced (Fig. 3, middle). The vibratory It has been known for long time that the variability pattern is very complex here, showing “ripples” in the of the vibration of the vocal folds themselves is very vibration of the vocal folds. A similar pattern may large. It has been quite difficult and lengthy, however, appear, e.g., during coughing. to evaluate the modification of the vibratory pattern Voice irregularities can also occur due to laryngeal of the vocal folds from the routinely used laryngostro- asymmetry. A slight phase shift of one of the vocal boscopic images. Better understanding of the dynamic folds with respect to the second one is a common behavior of the normal vocal folds should be helpful symptom of glottal asymmetry and can often be found in recognizing abnormalities occurring in voice in normal subjects, as demonstrated here in Fig. 1. disorders. Videokymography offers a relatively simple While in Fig. 1 the asymmetry does not cause any and powerful tool which can provide a more detailed major problem (the vibration is regular), under specific useful information in this respect. conditions (for instance at highest pitches or intensities) the asymmetry may cause that the left and ACKNOWLEDGMENT right vocal folds become desynchronized and the voice The research has been supported by the EUREKA sounds hoarse or diplophonic (Fig. 3, right, see also Project EU 723 “Artificial Larynx.” [10] for this phenomenon). REFERENCES 1. Švec J. G., Schutte H. K. Videokymography: high-speed line scanning of vocal fold vibration. J Voice 1996; 10: 201–205. 2. Schutte H. K., Švec J. G., Šram F. Videokymography: research and clinical issues. Log Phon Vocol 1997; 22: 152–156. 3. Švec J. G., Schutte HK, Šram F. Introduction to videokymography. (Video tape). Prague: Medical Healthcom, 1997. 4. Moore P., von Leden H. Dynamic variations of the vibratory pattern in the normal larynx. Folia Phoniatr 1958; 10: 205–238. 5. Hirano M. Clinical examination of voice. Wien: Springer- Fig. 3. Irregularities in the vibration of the middle part of normal Verlag, 1981. male vocal folds. Left: creaky voice with double opening, long closed phase, small amplitudes and visible mucosal waves. Middle: 6. Woo P. Quantification of videostroboscopic findings – breathy hoarse voice with no closed phase and “rippled” vibratory measurement of the normal glottal cycle. Laryngoscope pattern. Right: desynchronization of the vibrations of the left and 1996;106 (suppl. no. 79): 1–27. right vocal folds in falsetto register. (Total time displayed, ca. 18.4 7. Schutte H. K., Švec J. G., Šram F. First results of clinical ms, in all cases). application of videokymography. Laryngoscope 1998; 108: 1206–1210. 8. Šram F., Švec J. G., Schutte H. K. Possibilities for use of DISCUSSION AND CONCLUSION videokymography in laryngologic and phoniatric practice. Videokymography makes it possible to easily In: Dejonckere P. H., Peters H. F. M., editors. monitor the variability of the vibratory pattern of the Communication and its disorders: a science in progress. Proceedings 24th Congress International Association of vocal folds. The measuring position should be Logopedics and Phoniatrics, Amsterdam, the Netherlands, specified, however, in order to interpret the vibratory August 23–27, 1998. Vol. I. International Association of pattern correctly. In practice the measuring position Logopedics an Phoniatrics, 1999: 256–259. is easily found by means of the normal mode. The 9. Tanabe M., Kitajima K., Gould W. J., Lambiase A. examiner may adjust the measuring position by slightly Analysis of high-speed motion pictures of the vocal folds. moving (tilting) the endoscope. The perpendicularity Folia Phoniatr 1975; 27: 77–87. of the measuring line with respect to the glottis can be 10. Tigges M., Mergell P., Herzel H., Wittenberg T., Eysholdt adjusted by rotating the camera with respect to the U. Observation and modelling of glottal biphonation. 83 endoscope. Acustica – Acta Acustica 1997; : 707–714. 94 Chapter 8: Normal Variability in Videokymography Chapter 9: Videokymography: a New High-Speed Method for the Examination of Vocal-Fold Vibrations by J. G. Švec, F. Šram & H. K. Schutte Otorinolaryngologie a foniatrie /Prague/, 48(3): 155–162 (1999)

CHAPTER 9

Videokymography: a New High-Speed Method for the Examination of Vocal-Fold Vibrations

Švec J. G., Šram F., Schutte H. K.

Translated with permission from: Videokymografie: nová vysokofrekvenční metoda vyšetřování kmitů hlasivek. (In Czech). Otorinolaryngologie a foniatrie, 48(3): 155–162 (1999). © 1999, Česká lékařská společnost J. E. Purkyně

Švec: On Vibration Properties of Human Vocal Folds 97

Videokymography: a New High-Speed Method for the Examination of Vocal-Fold Vibrations

Jan G. Švec, František Šram, Harm K. Schutte*

Center for Communication Disorders, Medical Healthcom, Ltd.; Řešovská 10/491; 181 00 Prague 8, the Czech Republic (director: Ass. Prof. František Šram, M.D., Ph.D.)

and

*Groningen Voice Research Lab; Department of Biomedical Engineering – Artificial Organs, University of Groningen, Bloemsingel 10, 9712 KZ Groningen, the Netherlands (director: Prof. Harm K. Schutte, M.D., Ph.D.)

ABSTRACT Videokymography is a new optical high-speed method for investigation of vibrations which was developed especially for examination of vocal-fold vibrations. Videokymography is based on a modified CCD video camera, which is able to work in two different modes: standard and high-speed. In the standard mode the camera works as a normal commercial video camera providing 25 images (50 interlaced fields) per second. In the high-speed mode the camera delivers images from a single selected line with a frequency of almost 8000 line images/s. The successive line images are put below each other, creating a new videokymographic image monitoring vibration of the selected part of the vocal folds in time. A foot switch makes it possible to change instantaneously between the standard and high-speed modes. Ordinary videolaryngoscopic equipment with a powerful endoscopic continuous-light source can be used for the videokymographic examination of the vocal folds. Both the standard as well as high-speed images can be recorded by means of a normal video recorder, which makes the technique cost-friendly. The method is able to objectively evaluate important parameters of the vocal-fold vibration, such as the open, opening, closing and closed phases of the vibratory cycle, propagation of mucosal waves, left-right differences in phase or amplitude, etc. Videokymography provides more detailed information on voice disorders and considerably enriches laryngostroboscopy. There is no problem for videokymography to evaluate hoarse or unstable voices in which laryngostroboscopy fails. Also, the method is able to reveal structural irregularities on the medial surface of the vocal fold (e.g., sulcus glottidis) which can easily be overlooked in laryngostroboscopy. It is demonstrated how combination of a few laryngostroboscopic and videokymographic images can shortly and efficiently summarize important anatomical, physiological/pathological and vibrational properties of the laryngeal tissues in various patients.

Key Words: videokymography, high-speed imaging, vocal folds, vocal-fold vibration, laryngoscopy, laryngostroboscopy

INTRODUCTION a stroboscopic light source has been used, which Since vibration of the vocal folds is crucially creates an illusory slow motion of the vocal folds. important for the resulting quality of voice, its objective Laryngostroboscopy was introduced for the evaluation is an essential task for laryngologists and investigation of the vocal folds by Oertel in 1878 (11). phoniatricians. The vibration of the vocal folds is too Since that time laryngostroboscopy has brought a lot fast to be observed by human eye (under normal of valuable information on the mechanism of the vocal- conditions the frequency is in the range from ca. 70 to fold vibration and successively became the 1000 Hz) and it even cannot be registered by a video indispensable standard clinical method for the camera since its image rate is slower: 50 images (or examination of voice. In Czechoslovakia, the process fields, more specifically) per second. In order to of application and spreading of laryngostroboscopy visualize vocal-fold oscillation, most frequently needs to be credited to Seeman, Sedláčková and 98 Chapter 9: Videokymography: a New High-Speed Method especially to Sovák who published his monograph on The most powerful laryngoscopic systems, which laryngostroboscopy in two volumes in 1945 (17, 18). are not limited by the periodicity of the vocal-fold [Note: Unfortunately, this valuable textbook has not oscillation, use high-speed cameras working at rates been translated from Czech and remained overlooked more than 1000 images/s. The first high-speed in the scientific world abroad. The first internationally cinematographic system for the examination of the recognized textbook on laryngostroboscopy is the oscillation of the vocal folds was developed in the monograph of Schönharl (14) which was published 15 1930s in Bell Telephone Laboratories, USA (1). Since years after Sovák (7)]. (See also footnote). Modern that time, the high-speed cinematographic cameras laryngostroboscopic systems employ video equipment have been explored in a number of studies of the for registering the stroboscopic images. The newest vocal-fold vibration [detailed list of publications can computer-integrated videolaryngostroboscopic systems be found, e.g., in (6)]. Recently, the classical high- make it possible to apply a computer-aided image speed cinematographic systems have been supplanted analysis to evaluation of the vocal-fold vibration and by digital high-speed imaging systems (4, 5, 8, 23), its quantification (9, 10, 12, 13, 24). which present the most powerful devices for The main disadvantage of laryngostroboscopy is investigation and analysis of the vocal-fold vibrations that it works properly only with periodic oscillation of to date. These systems, however, remain rather the vocal folds. This makes it problematic to expensive for most of the hospitals and laboratories, laryngostroboscopically evaluate patients with hoarse therefore their use is limited to only few specialized or breathy voices, as well as patients unable to keep research institutes over the world. a stable pitch during phonation. When examining these voices there arise illusory, purely stroboscopic effects VIDEOKYMOGRAPHY which can lead to a faulty interpretation of the vocal- In 1994 a research project was carried out at the fold vibration (7). University of Groningen under the supervision of Prof. The limits of stroboscopy have stimulated a search Dr. H.K. Schutte, the purpose of which was the for other laryngoscopic methods, not limited by the development of a new, inexpensive method for periodic oscillations of the vocal folds. In 1970s, examination of various kinds of vocal-fold vibrations a German phoniatrician Gall invented the method of which would be suitable for a routine clinical use. As photokymography (2, 3), which was based on a specially a result of this project Švec designed a new optical modified photographic camera. The camera had method for observation of vibrations – video- a narrow slit/shutter (in front of the film) which moved kymography (16, 20–22). The method was practically during the image exposition. The moving slit enabled realized in cooperation with the Lambert Instruments to record the vibration of the vocal folds on BV company. a photographic film. Although the photokymographic The videokymographic device is based on a specially images appeared very promising for diagnostical modified CCD video camera which can function in purposes, the system encountered technical problems two different modes – standard and high-speed. The and has never overcome the stage of a prototype. principle is illustrated in Fig. 1. In the standard mode the camera functions as a normal commercial video camera, registering 50 fields/s (CCIR/PAL TV standard), and it provides a normal laryngoscopic view of the vocal folds. In the high-speed videokymographic mode the camera registers images from a single line of the CCD chip (Fig.1, left). The reduced amount of spatial data enables to increase the image rate of the camera to almost 8000 line images/s (more specifically 7812.5 line images/s in accordance with the CCIR/PAL TV Fig. 1. Two modes of the videokymographic camera. A) the laryngeal standard). The successive line images are put below image viewed by the standard mode of the camera. The image is each other and create a new, videokymographic image composed of horizontal lines. In the videokymographic mode (B) the camera registers images from a single active line at a high- monitoring the vibration of the selected part of the speed image rate. The consecutive line images are put below each vocal folds in time (Fig. 1, right). The videokymo- other and create a new videokymographic image monitoring the graphic image contains ca. 140 successive line images vibratory pattern of the selected part of the vocal folds. representing altogether the time of ca. 18 ms. Švec: On Vibration Properties of Human Vocal Folds 99

The standard and videokymographic modes of the Stuckrad, R. Wolf, Knittlingen, Germany) with a lens/ camera are used alternately. In practice, the standard adapter (Atmos or Kay Elemetrics 9117) were used mode is explored for finding the place of interest and for videokymography. A high-intensity (300 W) xenon positioning the active line of the camera to the desired continuous-light source (R. Wolf Auto LP 5130 or place. After aiming the active line at the selected Auto LP/FLASH 5135) was used for illuminating the spot, the camera is instantaneously switched into the larynx. A stroboscopic light source (R.Wolf 5021 or videokymographic mode (usually by means of a foot Kay Elemetrics 9106), color CCD video camera switch). A standard videolaryngoscopic setup is used (Atmos KP-C250AE or Panasonic GP-US502) and a for videokymography (rigid laryngoscope, light source, rigid endoscope (90° Lupenlaryngoskop R.Wolf video camera, TV monitor). The vocal folds are 4450.47 or 70° Kay Elemetrics 9106) with a lens/ illuminated by continuous (non-stroboscopic) light. adapter (Atmos or Kay Elemetrics 9116) were used Both the standard as well as the videokymographic for laryngostroboscopy. The video images from both video signals can be recorded via a standard types of examinations were recorded using a video commercial video cassette recorder (here it is advanta- cassette recorder (s-VHS Panasonic AG 7355). geous, similarly as in videostroboscopy, to use a video Those laryngoscopic, stroboscopic and videokymo- cassette recorder capable of providing separate static graphic images which best characterized the images of the image fields instead of the interlaced laryngologic state of the patient were selected from video frames). the video recordings. The images were digitized and fed into a PC using a video grabber (AV Master, MATERIAL AND METHODS FAST, Germany). Sequences of consecutive video- The initial testing phase of videokymography was kymographic images (as in Fig. 8D) were digitized carried out in 1994 in the Groningen Voice Research and concatenated by means of a frame grabber ZOB3 Lab in the Netherlands. Two male subjects without using a software OBR v. 3.5 (created and adapted for voice problems produced various kinds of phonations the videokymographic purposes by VIDIS company, (normal, breathy, pressed, etc.) which were registered Prague, the Czech Republic). The digital images were stroboscopically as well as videokymographically (21). further processed and composed together using the A black and white videokymographic CCD camera software package COREL DRAW! (Figs. 5–8). (Lambert Instruments BV, Leutingewolde, the Netherlands) was connected to a 90° rigid endoscope RESULTS (type von Stuckrad, R.Wolf, Germany) using a zoom Subjects without voice problems: objective/adapter (R. Wolf, type RIWO). Fig. 2 shows a stroboscopic image of a male subject A stroboscopic light source (Brüel & Kjaer 4914) was without any subjectively reported voice problems. used for stroboscopic examinations, a high-intensity There is a thickened blood vessel, a hemangioma, on continuous light-source (R. Wolf, AUTO-TCP- Lichtprojektor 5108) was used for videokymography. A Betamax video cassette recorder (SONY model SL-C9ES) was used to record the video signals. Besides the vibrating vocal folds, the vibration of violin strings (20, 22) and the airflow-induced vibration of a membranous slit were also observed in order to test the videokymographic system. Since 1996 the videokymographic system has been tested clinically in the Center for Communication Disorders, Medical Healthcom, Ltd. in Prague. More than 900 examinations of patients with physiological as well pathological findings have been carried out here. Each videokymographic examination of a patient was preceded by detailed complex phoniatrical examination, including recording of voice and speech Fig. 2. Stroboscopic image of male vocal folds as registered by the in a sound-treated room, investigation of a voice range standard mode of the camera. The horizontal line marks the position of the active line used during the videokymographic recording profile and videolaryngostroboscopy. A videokymo- shown in Fig. 3. (From Švec, J.G., Schutte, H.K.: Videokymography: graphic camera (Lambert Instruments BV, Leutinge- high-speed line scanning of vocal fold vibration. J. Voice, 10, 1996: wolde, NL) and a 90° rigid endoscope (type von 201–205, used with permission). 100 Chapter 9: Videokymography: a New High-Speed Method

Fig. 3. Videokymogram of the vocal folds followed by the propagation of mucosal the vocal-fold vibrations waves is visible here. In the closing phase there can be registered at the place marked in Fig. 2 (total observed the movement of the upper as well as of the time displayed, ca. 18 ms). lower margins of the vocal folds. Fig. 4 schematically The opening movement illustrates the most important features of the normal of the vocal folds followed vocal-fold vibration and relates the videokymographic by the propagation of mucosal waves can be view with stroboscopic images. seen here. During the closing phase the Subjects with voice disorders: movement of the upper Four illustrative examples of laryngeal findings in as well as of the lower margin of the vocal folds patients are described here, which are documented by is visible. See the characteristic laryngoscopic, laryngostroboscopic and schematic illustration in videokymographic images of each patient. Fig. 4. Patient no. 1 (Fig. 5): female, age 69. Diagnosis: chronic laryngotracheitis, slight atrophy of the left vocal fold, compensational hypertrophy of the the right vocal fold which did not cause any noticeable ventricular fold left. There was a tendency towards problems during phonation. The line in Fig. 2 marks hyperadduction of the vocal folds. The voice disorder the place which was examined videokymographically. arose 3 years before the examination as a consequence The videokymographic image is given in Fig. 3. It of laryngitis. clearly shows open and closed phases of the glottal Examination results: the voice was perceptually cycle. An opening movement of the upper margins of evaluated as hoarse and strained. Laryngoscopy

Fig. 4. Schematic illustration of the characteristic features of the normal vocal-fold vibration as compared with stroboscopy and videokymography. Švec: On Vibration Properties of Human Vocal Folds 101

Fig. 5. Laryngoscopic, stroboscopic and videokymographic findings Fig. 6. Laryngoscopic, stroboscopic and videokymographic in patient no. 1 with slight hoarseness and slight hyperadduction. findings in patient no. 2 with slight hoarseness. A) maximally closed A) glottal closure during phonation. B) maximally open glottis glottis during phonation. There remains a gap in the membranous during phonation. The vibrational amplitude is reduced bilaterally, part as well as in the posterior part of the glottis. Chronic edema is a bulging of the left ventricular fold is apparent here. C) breathing, visible in the middle third of the membranous part of the left vocal left vocal fold is thinner and shows signs of atrophy. D) fold. B) vocal folds during a closing phase of the vibratory cycle; the videokymogram of a phonation at a frequency of ca. 200 Hz (see A arrows mark a longitudinal furrow (sulcus glottidis) at the medial for recording position, total time displayed ca. 18 ms). A prolonged surface of the right vocal fold. A small polyp is visible in the closed phase (of ca. 70% duration of the glottal cycle, suggesting posterior, caudal part of the left vocal fold. C) breathing; an hyperadduction), with a right-left swinging of the glottis during the excavation of the right vocal fold and the polyp on the left vocal closed phase is evident here. Mucosal waves propagate over the fold is visible. D) videokymogram of a phonation at a frequency of upper surface of the vocal folds bilaterally, lower margin of the ca. 250 Hz (the measurement position is indicated in A – the vocal fold is visible on the left during the closing phase. camera was slightly rotated with respect to the endoscope in order to achieve perpendicularity of the measurement position to the showed slightly inflamed vocal folds of a pink-grayish glottal axis; total time displayed ca. 18 ms). The closed phase is color with a smooth, glossy surface. The right vocal markedly reduced (the vocal folds touch just for a short moment), the reflexes of light depicted as diagonal lines at the upper surface fold was without any signs of atrophy, the left vocal of the vocal folds reveal the propagation of mucosal waves bilaterally. fold was slightly atrophic and thinner. Gross mobility The arrows mark a double peak reflecting the furrow on the medial of the larynx was undisturbed. Under stroboscopic surface of the right vocal fold. light, both vocal folds were observed to vibrate in their full length, their oscillations appeared unstable Videokymography (Fig. 5D) revealed a prolonged and their amplitudes of vibration were slightly reduced closed phase (ca. 70% of the cycle) as a sign of a slight (slightly larger amplitude was observed on the right). spasticity. Furthermore, there was found an “S-shaped” Mucosal waves were present bilaterally. There was course of the glottal closure, which indicates a left- a posterior triangular glottal gap in the glottal closure right swinging of the glottis during the clased phase. (Fig. 5A). The left ventricular fold was bulged into This gives evidence on phase asymmetry in the vocal- a paramedial position during phonation (Fig. 5B). fold vibration. Other videokymographic features visible 102 Chapter 9: Videokymography: a New High-Speed Method in Fig. 5D support the stroboscopic findings: the Patient no. 3 (Fig. 7): male, age 70. Diagnosis: partial vibratory amplitude is reduced, the upper margin of ankylosis of the cricoarytenoid joint right and deep left vocal fold shows slightly larger amplitude than vocal-fold scarring right (a consequence of that one on the right, mucosal waves are apparent on a post-surgical complication following removal of both the vocal folds. A lower margin is visible on the a ventricular-fold cyst right 30 years before the left atrophic vocal fold during the closing phase. examination); laryngeal paralysis left accompanied by Besides of these findings, there was observed a slightly ankylosis of the cricoarytenoid joint (after a viral asymmetrical position of the soft palate which was infection 1 year before the examination; accompanied pulled towards the right side (an evidence of a partial by dysphagia when swallowing fluids). innervation disorder of the soft palate left). The Examination results: the voice was perceptually laryngostroboscopic as well as the videokymographic evaluated as hoarse, breathy, almost aphonic. findings lead us to suspect a partial innervation Laryngoscopy (Fig. 7A) showed good mobility of the disorder of the larynx at the left side. Patient no. 2 (Fig. 6): female, age 40. Diagnosis: chronic laryngotracheitis, state after debulking a chronic edema on the right vocal fold and removal of a vocal-fold polyp left 2 years before the examination. Examination results: the voice was perceptually evaluated as hoarse with slight breathiness. Laryngoscopy (Fig. 6C) revealed slight chronic inflammation of the laryngeal (and tracheal) mucosa. The vocal folds were of a pink-grayish color, with broadened vessels. The right vocal fold was atrophic with a thin excavated margin. The left vocal fold was slightly thickened due to a residuum of a chronic edema localized on the upper surface of the membranous part of the fold. At the borderline between the anterior and middle thirds of that vocal fold, there was a small polyp placed slightly subglottaly (Figs. 6B, C). The gross mobility of the vocal folds was preserved. A 3-mm-long synechia was found at the anterior commissure. Under stroboscopic light, both the vocal folds were observed to vibrate in their full length; their amplitude was slightly reduced bilaterally. Glottal closure revealed an insufficiency in the middle third as well as in the posterior third of the vocal fold (Fig. 6A). Fig. 6D shows a videokymogram of the vibratory Fig. 7. Laryngoscopic, stroboscopic and videokymographic findings pattern of the vocal folds taken at the position marked of the patient no. 3 with strong breathiness and hoarseness. A) in Fig. 6A. The glottis remains open through most of breathing; both vocal folds are atrophic with delineated longitudinal furrows; a synechia is present in the anterior commissure, the left the cycle, touching each other only for a short moment, arytenoid cartilage is tilted ventro-medially over the glottal midline. which confirms the stroboscopic finding of glottal B) maximally closed phase of the vocal folds during the phonation insufficiency (causing the slight phonatory showing a wide glottal gap. The arrow marks a furrow which breathiness). Light reflexes in the form of diagonal borders the thin vibrating margin of the right vocal fold. C) videokymogram of the posterior part of the vocal folds (see B for lines reflect mucosal waves propagating bilaterally on the measuring position). Only left vocal fold vibrates here at the upper surfaces of the vocal folds. A double peak a frequency of ca. 120 Hz, the vocal folds are separated by a wide (marked by the arrows in Fig. 6D) reveals a furrow on glottal gap. D) videokymogram of the middle part of the glottis the medial surface of the right vocal fold (sulcus (see B for the measurement position, the phonation is different from C). A wide glottal gap remains here, the medial margin of the glottidis). On the basis of this videokymographic right vocal folds vibrates irregularly, the left vocal fold vibrates at finding, the furrow was later discovered also in a frequency of ca. 150 Hz. Signs of oscillation are visible also on the stroboscopy (see arrows in Fig. 6B). right ventricular fold. The arrow marks the border of the vibrating mucosal margin. (Total time displayed in C and D ca. 18 ms). Švec: On Vibration Properties of Human Vocal Folds 103 right arytenoid cartilage in the range from lateral to paramedial position. The left arytenoid cartilage was immobile, tilted ventro-medially, visually crossing the glottal midline. The right ventricular fold was partially mobile up to paramedial position, the left one was immobile and atrophic. A ca. 5-mm-long synechia was found in the anterior part of the vocal folds. The vocal folds were of a pink-grayish color, slightly inflamed, having thin excavated margins with bilaterally delineated furrows. The right vocal fold was slightly diffusely thickened and adducted only in its dorsal half within a restricted range (ca. 2 mm) from the lateral to paramedial position. The left atrophic vocal fold had a thin excavated margin and was immobile, positioned intermedially. Laryngostroboscopic examination showed a vibration of a thin, partially separated medial part of the mucosa at the middle membraneous third of the right vocal fold. The oscillations were irregular of a reduced amplitude. The left vocal fold was vibrating in its full length, except of the most anterior part related to synechia. Its vibration amplitude was reduced, mucosal wave was observed in the medial third of the membranous part of the vocal fold. A wide glottal gap Fig. 8. Laryngoscopic, stroboscopic and videokymographic findings was found during the closed phase (Fig. 7B). of the patient no. 4 with a ventricular voice. A) breathing; on the right, there is a vocal fold with widened blood vessels; on the left Videokymographic investigation shown in Fig. 7C there is a structure remaining after cordectomy. The ventricular was done in the posterior part of the glottis (see Fig. folds are hypertrophic. B) Phonation, closed phase. The ventricular 7B for the position). The right vocal fold did not folds touch each other. The line marks the measurement position oscillate here, the left vocal fold showed oscillations for videokymograms C and D (the camera was slightly rotated in order to make the active line approximately perpendicular to the at a frequency of ca. 120 Hz. A wide glottal gap longitudinal axis of the pseudoglottis). C) an episode of a ventricular remained between the vocal folds. Fig. 7D presents voice of a good quality (at frequency of ca. 120 Hz). Large amplitudes a videokymogram obtained from the middle part of of the ventricular folds as well as vigorous mucosal waves are the glottis during another phonation. The thin medial prominent here (total time displayed ca. 18 ms). D) an episode of a hoarse voice produced by irregular oscillations of the ventricular margin of the right vocal fold was oscillating here at folds with small vibratory amplitudes. an irregular frequency, apparently higher than the frequency of ca. 150 Hz observed on the left vocal the right vocal fold with a smooth surface and fold. An irregular vibration with a small amplitude broadened blood vessels. Gross mobility of the fold was present on the right ventricular fold. The frequency was preserved up to paramedial position. On the left differences between the vibrations of the two vocal folds side, a structure was left after the cordectomy. The and their oscillatory irregularities unveil the origin of ventricular folds were hypertrophic, concavely bulged. the hoarseness in this patient; the wide glottal gap is They approximated each other during phonation related to the strong breathy component of the voice. (Fig. 8B), reached a complete closure and oscillated Patient no. 4 (Fig. 8): male, age 69. Diagnosis: state with an irregular frequency. Signs of mucosal waves after cordectomy left and deep scarring of the vocal were noted at the surfaces of the ventricular folds. fold right as a consequence of radiation therapy 10 The videokymogram in Fig. 8C shows one of the best years before the examination; state after successful (least hoarse), relatively high-pitched (frequency ca. mastering of ventricular voice. 120 Hz), ventricular phonations. Large oscillatory Examination results: the voice was perceptually amplitude is apparent here as well as vigorous mucosal evaluated as low-pitched with variable degree of waves on the ventricular folds. Slightly worse and hoarseness–there were recorded occasional aphonic perceptually hoarse phonation is shown in Fig. 8D in 4 sequences, hoarse phonations with a strong breathy consecutive videokymographic images. Apparently component, as well as phonations with only slight irregular oscillations of the ventricular folds with small degree of hoarseness. Laryngoscopy (Fig. 8A) showed amplitudes are visible here. 104 Chapter 9: Videokymography: a New High-Speed Method

DISCUSSION AND CONCLUSION videokymography is its relatively low price since the The developed videokymographic system makes it camera does not require any non-standard recording possible to relatively easily and quickly monitor vocal- media and the video signal can be recorded via, e.g., fold vibrations. Videokymographic images can be used a standard commercially available video cassette for an objective evaluation and subsequent analysis of recorder. important parameters of the vocal fold vibration (e.g., frequency, amplitude, irregularities, left-right asym- ACKNOWLEDGMENT metry, propagation of mucosal waves or duration of The design and the development of the the various phases of the glottal cycle such as open, videokymographic method was realized in 1994 during opening, closing and closed phases). These parameters, J. Švec’s research stay in the Groningen Voice reflecting the physiologic/pathologic state of the vocal Research Lab and in the Center for Biomedical folds, cannot be objectively evaluated by means of Technology at the University of Groningen, the videolaryngostroboscopy (especially when the voice is Netherlands. The stay was partially financially more or less perturbed). supported by the Centre for Biomedical Technology In clinical practice the videokymographic method and by the TEMPUS JEP 1941 programme. The substantially enriches the diagnostic possibilities of authors would like to express their gratitude to the laryngostroboscopy. Laryngostroboscopy provides Lambert Instruments BV company (Leutingewolde, information on appearance and mobility of the the Netherlands) for the technical realization of the laryngeal structures during vibration and on that basis videokymographic camera. The thanks belong also to makes it possible to qualitatively evaluate some of the the Hospimed company (Prague, the Czech Republic) vibratory features (regularity, shape of glottal closure, for providing us with the R. Wolf light sources (Auto etc.). Videokymography complements stroboscopy LP 5130 and Auto LP/FLASH 5135 xenon) and to because it objectively reveals the dynamic behavior of Kay Elemetrics Corp (Lincoln Park, USA) for the vocal folds and other laryngeal structures in detail continuing interest in the development of video- and it can be used for quantification of the vibratory kymography. Since 1996 the research has been parameters. The advantage of the videokymographic supported by the EUREKA EU 723 Artificial Larynx high-speed imaging becomes apparent especially when project. investigating irregular vocal-fold oscillations such as, e.g., severely dysphonic voices in which the FOOTNOTE: An important improvement came from Van stroboscopic method fails. Videokymography also den Berg in Groningen, who designed the delta-f generator, makes it possible to unveil details such as surface which made the use of stroboscopy more practical and irregularities of the medial margin of the vocal folds applicable in clinical settings. [Van den Berg Jv. A delta-f- which can easily be overlooked in stroboscopy (recall generator and movie-adapter unit for laryngostroboscopy. Fig. 6D-sulcus glottidis). Practica Oto-Rhino-Laryngologica 1959; 21(5):355–363.] Combinations of the videostroboscopic and (This text was not incorporated in the original Czech version videokymographic images, such as those shown in of the paper). Figs. 5–8, enable to understand the mechanism of a voice disorder in more detail. The combined images provide a more complex view of the anatomical REFERENCES 1. Farnsworth, D. W.: High-speed motion pictures of the changes as well as of the functional state of the vocal human vocal cords. Bell Lab. Record, 18, 1940, 203–208. folds. One of the most important advantages of the 2. Gall, V., Gall, D., Hanson, J.: Larynx-Fotokymografie. combination of these examination methods is the Arch. klin. exp. Ohr. -, Nas. - u. Kehlk. Heilk., 200, 1971, simplicity and instructive description of the laryngeal 34–41. findings by means of the images. The documentation 3. Gross, M.: Endoskopische Larynx-Fotokymografie. of the selected images makes it possible to arrive at Bingen, Germany: Renate Gross Verlag, 1988. a more detailed diagnosis of voice disorders, to 4. Hertegård, S., Lindestad, P.-Å.: Vocal fold vibrations evaluate the progression of the morphologic changes studied during phonation with high-speed video imaging. in time, as well as to evaluate the results of voice Karolinska Institute, Huddinge University Hospital Phoniatric and Logopedic Progress Report, 9, 1994, 33– therapy. It enables to discover minimal organic as well 40. as nonorganic pathologic changes of the vocal folds. 5. Hess, M. M., Herzel, H., Köster, O., Scheurich, F., Gross, Thanks to these merits videokymography appears M.: Endoskopische Darstellung von Stimmlippen- helpful in laryngologic practice (16, 19), as well as in schwingungen. Digitale Hochgeschwindigkeitsaufnahmen basic voice research. A considerable advantage of mit verschiedenen Systemen. HNO, 44, 1996, 685–693. Švec: On Vibration Properties of Human Vocal Folds 105

6. Hirano, M.: Clinical examination of voice. Wien: 16. Schutte, H. K., Švec, J. G., Šram, F.: First results of Springer-Verlag, 1981. clinical application of videokymography. Laryngoscope, 7. Hirano, M., Bless, D. M.: Videostroboscopic examination 108, 1998, 1206–1210. of the larynx. San Diego, CA: Singular Publishing Group, 17. Sovák, M.: Kmitání hlasivek ve světle 1993. laryngostroboskopie. [Vibration of the vocal folds in the 8. Honda, K., Kiritani, S., Imagawa, H., Hirose, H.: High- laryngostroboscopic light. In Czech]. Praha: Česká speed digital recording of vocal fold vibrations using akademie věd a umění, 1945. a solid-state image sensor. In T. Baer, C. Sasaki, K. S. 18. Sovák, M.: Stroboskopický výzkum hlasové pathologie. Harris (Eds.) Laryngeal function in phonation and Studie o poruchách fonačního mechanismu. respiration. (pp. 489–491). Boston/Toronto/San Diego: [Stroboscopical research on voice pathology. A study on A College-Hill Press, Little, Brown and Co., 1987. disorders of the organ of phonation. In Czech]. Praha: 9. Isogai, Y.: Laryngostrobography by the newly developed Česká akademie věd a umění, 1945. strobo-motion–analyzer. Larynx Jpn., 6, 1994, 91–96. 19. Šram, F., Schutte, H. K., Švec, J. G.: Clinical applications 10. Isogai, Y.: Analysis of the vocal fold vibration by the of videokymography. In G. McCafferty, W. Coman, R. laryngo-strobography-improvements of the analytic Carroll (Eds.) XVI. World Congress of Otorhino- function. Larynx Jpn., 8, 1996, 27–32. laryngology Head and Neck Surgery, Sydney ’97: 11. Oertel, M. J.: Über eine neue “laryngostroboskopische” Proceedings, vol. 2. (1681–1684). Bologna: Monduzzi Untersuchungsmethode des Kehlkopfes. Zbl. Med. Editore, 1997. Wissensch., 16, 1878, 81–82. 20. Švec, J.: Studium mechanicko-akustických vlastností 12. Rosen, S., Fourcin, A., Faulkner, A., Hazan, V., Miller, lidského hlasu. [Studies on the mechanic-acoustic D.: Development in phonetics for the ENT profession. properties of the human voice. Thesis. In Czech]. ENT News, 5, 1996, 18–19. Olomouc, Palacký University, Faculty of Natural 13. Saadah, A. K., Galatsanos, N. P., Inagi, K., Bless, D.: Sciences, Department of Experimental Physics, 1996. Deformation analysis in studying the effect of Botulinum 21. Švec, J. G., Schutte, H. K.: Videokymography: high- Toxin to rat vocal folds. In T. Wittenberg, P. Mergell, M. speed line scanning of vocal fold vibration. J. Voice, 10, Tigges, U. Eysholdt (Eds.) Advances in quantitative 1996, 201–205. laryngoscopy: proceedings of the 2nd ‚Round Table‘ 22. Švec, J. G., Schutte, H. K., Šram, F.: Introduction to Advances in quantitative laryngoscopy using motion-, videokymography. (Video film). Praha: Medical image- and signal analysis, Erlangen 1997 (pp. 39–50). Healthcom, 1997. Göttingen: Universitäts-HNO-Klinik Göttingen, 1997. 23. Wittenberg, T., Moser, M., Tigges, M., Eysholdt, U.: 14. Schönharl, E.: Die Stroboskopie in der praktischen Recording, processing, and analysis of digital high-speed Laryngologie. Stuttgart: Georg Thieme Verlag, 1960. sequences in glottography. Machine Vision and 15. Schutte, H. K., Švec, J. G., Šram, F.: Videokymography: Applications, 8, 1995, 399–404. research and clinical issues. Log. Phon. Vocol., 22, 1997, 24. Woo, P.: Quantification of videostroboscopic findings – 152–156. measurement of the normal glottal cycle. Laryngoscope, 106 (suppl. no. 79), 1996, 1–27. 106 Chapter 9: Videokymography: a New High-Speed Method Chapter 10 Addendum

CHAPTER 10

Addendum

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ADDENDUM

Videokymography proved to be a very useful tool Figure A1 shows that the vibration is not really which allows to obtain detailed information on the disordered during the abrupt chest-falsetto transition, dynamic behavior of the vocal folds during chest- as it has been assumed from the investigations of falsetto transitions. Below, there are presented some Rubin and Hirt [7]. Both the vocal folds vibrate examples which were presented to international synchronously during the transition with a distinct conferences [1–5] and are in preparation for future (complex, “rippled”) pattern. The shift from the publications. “rippled” to falsetto pattern (causing the actual sudden Figure A1 complements the results from Chapters change of frequency of voice) is accomplished within 2 and 4 and reveals the change of vibratory pattern of almost a negligible time interval of one vibration cycle the vocal folds at the moment of the chest-falsetto (ca. 3 ms). Accomplishment of such a quick change of leap, as viewed in videokymography. At the beginning frequency lies far beyond the capabilities of laryngeal of the transition, the vocal folds vibrate in chest muscles in terms of their maximal contraction speed (modal) register at the frequency of ca. 200 Hz. The [6;8], and gives strong evidence that such a change of closure of the vocal folds is untypically short for the frequency is a bifurcation phenomenon. chest vibratory pattern, however. The vibration Figure A2 presents a sequence of videokymographic successively looses its simple shape and the pattern is images showing the formation of the subharmonic modified by a “ripple” which increases from cycle to vibratory pattern observed in Chapters 2 and 3. The cycle until the vibration instantly shifts into a falsetto simple-shaped glottal cycle (of the chest register) pattern with the resulting frequency of ca. 300 Hz. successively transforms into a subharmonic pattern

Fig. A1. Chest-falsetto jump as viewed in the sequence of eight consecutive videokymographic images. The same subject as investigated in Chapters 2, 3 and 5. The frequency transforms from ca. 200 Hz to ca. 300 Hz. The measuring position was approximately in the middle of the vocal folds, perpendicular to the glottis. (Concatenation of the VKG fields was done by the same method as used in Chapter 9).

Fig. A2. Eight successive videokymograghic fields showing the change from normal (chest register) to a subharmonic vibratory pattern of the vocal folds. The frequency transforms from ca. 150 Hz to ca. 75 Hz. The same subject as investigated in Chapters 2, 3 and 5 The measuring position was approximately in the middle of the vocal folds, perpendicular to the glottis. 110 Chapter 10: Addendum

Fig. A3. Simulation of a superposition of two sinusoidal vibrations with the fundamental frequencies related by the f2:f1 = 3:2 ratio, which shows the possible mechanism of creation of a subharmonic pattern. The resulting superposed signal (top) shows features similar to the PGG and EGG signals in Fig. 2 in Chapter 3. which is composed of two glottal cycles, the first simple- shaped, the second one “rippled”. The “rippled” shape of the glottal cycle observed here indicates a relationship with the unstable vibratory pattern observed at the moment of chest-falsetto transition in Fig. A1. An interesting role seems to be played by the 3:2 ratio observed in this subject as the typical magnitude of the chest-falsetto leap (Chapter 2) as well as the ratio between the two lowest resonance frequencies of the vocal folds (Chapter 5). The 3:2 ratio is hypothesized to play also a role for the formation of the subharmonic pattern of the vocal folds (Chapter 3). The possible mechanism is illustrated in Fig. A3. The figure presents a simple simulation of combination of a stable sinus vibration (frequency 140 Hz) to which a second vibration with a frequency 210 Hz (e.g., 3/2 times higher than 140 Hz) and a successively increasing amplitude is added. For simplicity, the nonlinear effects are neglected here. The result is a complex Fig. A4. A patient (male, age 22) suffering from a mutational voice vibration with a subharmonic pattern which in many disorder (prolonged mutation). (A) Breathing. (B) Closed and (C) open phases of the vocal folds vibrating in a chest register as seen in aspects resembles the subharmonic pattern of the real videostroboscopy. Images (D, E, F) show vibration of the vocal vocal folds (compare Figure A3 to A2 and also to folds in falsetto register. The images from the open phase of this Figure 2 in Chapter 3). In accordance with the results register (D, E) reveal anterior-posterior differences which indicate of Chapter 5, the two vibrations illustrated in Figure the presence of the mode x-2. An almost complete glottal closure, except of a small gap in the posterior part, is visible in (F). A3 might be related, e.g., to the modes x-1 and x-2. While the contribution of the x-2 mode to the complex subharmonic vibratory pattern would not be posterior differences, typical for the x-2 mode, have surprising, the role of this mode in the mechanism of been reported. However, in our latest investigations the chest-falsetto transition has not been expected, of patients with mutational dysphonia, suffering from since in neither of these two registers the anterior- voice instability and occurrence of spontaneous chest- Švec: On Vibration Properties of Human Vocal Folds 111 falsetto leaps in speech, the anterior-posterior needed to confirm this hypothesis, however. Unfortu- differences were detected (Figs. A4 and A5). This nately, the experiments put rather high demands on finding indicates that the x-2 mode might, indeed, the investigated subjects in terms of the ability of play some role in the production of spontaneous chest- voice control, which makes gathering of the data from falsetto leaps, at least in some subjects. large amount of subjects not an easy task. Never- The initial data from Chapters 2 and 5 are in theless, the initial results obtained within the accordance with the hypothesis expressed in Chapter dissertation appear promising in terms of providing 2 that the magnitude of the pitch jump during chest- fundamental data on the biomechanical properties of falsetto transition is related to the adjustment of the the vocal folds. (lowest) resonance frequencies of the vocal folds. If The initial results obtained from applying such a relationship would indeed exist, the information videokymography to basic as well as clinical investi- on magnitude of the frequency jump during abrupt gations of voice prove that videokymography can be chest-falsetto transition might be used to derive helpful in obtaining new, detailed information on the information on the resonance properties of the vocal vibration properties of the vocal folds as well as to folds which are highly problematic to measure. More contribute to a more objective diagnosis of voice investigations and data from more subjects are highly disorders.

Fig. A5. Videokymographic images of an abrupt chest-falsetto transition in the same patient as shown in Fig. A4. The measurement position is indicated in Fig. A4 (B and E). (G) Detail of the vibratory pattern of the chest register (frequency ca. 100 Hz) with a prominent long closed phase. (H) Detail of the falsetto register (frequency ca. 400 Hz) with a short closed phase and smaller amplitude of vibration. (I) Chest-falsetto jump (the frequency transforms from ca. 200 Hz to ca. 390 Hz). Note the transition pattern within the time interval between 60–90 ms. (J) Falsetto-chest jump (the frequency transforms from ca. 370 Hz to ca. 190 Hz). A complex vibration pattern can be seen during the transition between 20–70 ms. 112 Chapter 10: Addendum

REFERENCE LIST (Lecture). PEVOC III, 3rd Pan European Voice Conference. Utrecht, the Netherlands, August 26–29, 1999. [1] Švec JG, Schutte HK, Šram F: Voice Registers in the [Presented by J. Švec]. Light of Videokymography. (Lecture). 26th Annual [5] Šram F, Švec J: Results of Videokymographic Symposium: Care of the Professional Voice. Philadelphia, Examinations by Functional Voice Disorders/Die PA, June 2–7, 1997. [Presented by J. Švec]. Resultate der Videokymographie bei funktionellen [2] Švec JG, Schutte HK, Šram F: Videokymography: Stimmstörungen. (Lecture). Deutsche Gessellschaft für Introduction, Vibration of Normal Vocal Folds, Voice Phoniatrie und Pädaudiologie Wissenschaftliche Jahres- Registers. (Lecture). 2nd ‘Round Table’ Advances in tagung, Marburg, Germany, October 1–3, 1999. [Presented Quantitative Laryngoscopy using Motion-, Image- and by F. Šram]. Signal Analysis. Erlangen, Germany, July 18–19, 1997. [6] Alipour F, Titze I. Active and passive characteristics of [Presented by J. Švec]. the canine cricothyroid muscles. J Voice 1999; 13(1): 1– [3] Berry D, Švec JG: A gentle whiff of chaos from patients, 10. singers and experiments. (Lecture). 28th Annual [7] Rubin HJ, Hirt CC. The falsetto. A high speed cin- Symposium: Care of the Professional Voice. Philadelphia, ematographic study. Laryngoscope 1960; 70: 1305–1324. PA, June 2–6, 1999. [Presented by D. Berry and J. Švec]. [8] Sundberg J. Maximum speed of pitch changes in singers [4] Švec JG, Šram F, Schutte HK: Sudden Changes in the and untrained subjects. J Phonetics 1979; 7: 71–79. Vocal Fold Vibration: Videokymographic Observations. Summary and Conclusions

Summary and Conclusions Samenvatting en conclusies

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SUMMARY AND CONCLUSIONS

Chapter 1 introduces the subject of the dissertation subjects. An analogy with an “overblown flute” served and presents its two main aims: (A) to provide new as a model when producing the register leaps. The information on phenomena related to transition subject started to phonate at comfortable loudness in between chest and falsetto voice registers and (B) to chest register and kept a stable pitch while smoothly develop a new, cost-friendly method which would increasing the expiratory airflow. This maneuver provide more detailed information on the vibratory resulted in a spontaneous abrupt change of the behavior of the vocal folds. fundamental frequency of voice. The maneuver was The problem of voice registers presents a highly produced across the whole range of fundamental important but highly controversial issue of a singing frequencies in a normal male subject and its effect on voice and has not been fully solved yet. The first part of the fundamental frequency of voice was analyzed. the dissertation pays attention especially to one aspect The observed effects differed among three regions of the problem of voice registers – sudden changes of of voice. (1) In the region of low fundamental frequencies vibration of the vocal folds that occur (often (110–165 Hz; pitches A2-E3), changes from the chest spontaneously and involuntarily) during the transition register into an irregular, perceptually rough voice between chest (modal) and falsetto registers (chest- were observed. A production of a tone with F0/2 falsetto jumps). Experimental approach is used here subharmonic frequency (sounding an octave below to obtain new information on these voice phenomena. the original tone) was detected within this region. Chest-falsetto jumps are interpreted as bifurcations, (2) In the region of medium fundamental frequencies i.e., events known from the theory of nonlinear (165– 400 Hz; pitches E3-G4) the maneuver resulted dynamics. An important insight to the problem of in leaps from chest to falsetto register. The magnitude voice registers promises to be gained by identification of the pitch change was found to be around seven of modes of vibration of the vocal folds (eigenmodes) semitones (musical interval of a fifth), measured at which determine the resulting vibratory pattern of the the starting frequency of 165 Hz (tone E3). The interval vocal folds. Information on properties of the important of seven semitones corresponds to the frequency ratio eigenmodes of the vocal folds has been missing to of 3:2 (relating the two fundamental frequencies of a large extent. The dissertation provides new voice after and before the leap, respectively). With experimental data on the eigenmodes and rising the starting fundamental frequency, the eigenfrequencies of the living vocal folds which are magnitude of the pitch change (in terms of semitones) measured and visualized as resonance frequencies decreased. (3) In the upper-frequency region (400–660 Hz; and resonance modes. pitches G4-E5) only the falsetto register could be Information on vocal-fold vibration has been limited produced. due to the difficulties of the routinely used Chapter 3 observes in detail the F0/2 (sounding an laryngoscopic methods such as laryngostroboscopy octave below an original tone) subharmonic vibratory with registering irregularities in the resulting vibratory pattern which was observed in Chapter 2. Simultaneous pattern on one side, and due to inaccessibility of the electroglottographic and photoglottographic measure- very powerful, but highly expensive high-speed imaging ments revealed two different open phases within systems on the other side. There has been a need for a subharmonic cycle – the first shorter with a simple a cost-friendly method, which would allow more shape, the second longer with a shape containing detailed examination of the vocal-fold vibration a “ripple”. Such parameters as the large open quotient including the transitional and irregular vibratory states. (ca. 0.8) and the high airflow values (ca. 1000 cm3/s) The second part of the dissertation is devoted to the distinguished this phonation from the vocal fry (pulse) development and application of a new method for register. investigation of vocal fold vibration called Using an electronic divider to track the subharmonic videokymography. frequency, a method has been developed to observe Chapters 2–5 form the first part of the dissertation the subharmonic vibration of the vocal folds devoted to problems related to abrupt changes of stroboscopically. The stroboscopic visualization frequency during chest-falsetto transition and the revealed that the vocal folds were not desynchronized dynamic characteristics of the vocal folds. but displayed a complex symmetrical vibratory pattern. Chapter 2 introduces a special phonatory maneuver An unusual mucosal movement was observed during for eliciting abrupt chest-falsetto transitions in living the “ripple”: it was characterized by an opening 116 Summary and Conclusions movement of the upper margins which interrupted was close to 3:2 which resembles the leap ratio of the the closing movement of the vocal folds. An chest-falsetto leap measured in chapter 2. explanation is offered that this vibratory pattern arises Different resonance modes of vibration of the vocal as a consequence of detuning of the usually identical folds (observed as distinct lateral-medial oscillations frequencies of the dominant modes of the vocal folds, with one, two and three half-wavelengths along the with 3:2 entrainment replacing the normal 1:1 pattern. glottal length, respectively) were associated with these Chapter 4 returns to the phenomena of chest- resonance frequencies. It is hypothesized that falsetto jumps, which are studied in detail in an excised simultaneous excitation of these modes of vibration human larynx and in 3 living subjects (one female and could produce the complex F0/2 subharmonic vibratory two male). The chapter offers a new concept of the pattern observed in chapter 3. Besides of the vocal mechanism of abrupt chest-falsetto register transitions folds also other laryngeal structures responded to based on the bifurcation effects known from the theory external excitation: below 100 Hz, the vibrations of of nonlinear dynamics. Data from the excised larynx the ventricular folds (with the resonance frequency of revealed that a small and gradual change in tension of ca. 70 Hz), aryepiglottic folds and arytenoid cartilages the vocal folds could cause an abrupt change of register were dominant in the larynx. and pitch. This gives evidence that the register jumps Chapters 6–9 form a second section of the are manifestations of bifurcations in the vocal fold dissertation devoted to the development and vibratory mechanism. A hysteresis was observed; the application of a new method for examination of vocal upward register jump occurred at higher pitches and fold vibration. tensions than the downward jump. Due to the Chapter 6 introduces a digital technique for high- hysteresis the chest and falsetto registers can be speed visualization of vibration called video- produced with practically identical laryngeal kymography that was developed and applied to the adjustments within certain range of longitudinal vocal folds. The system uses a modified video camera tensions. which is able to work in two modes: high-speed (nearly The magnitude of the frequency jump was measured 8000 images per second), and standard (50 images as the “leap ratio” F0F :F0C (fundamental frequency of per second in CCIR/PAL standard). In the high-speed the falsetto related to that of the chest register) and mode the camera selects one active horizontal line alternatively expressed as a corresponding musical (transverse to the glottis) from the whole laryngeal interval, termed the ”leap interval”. Ranges of this image. The successive line images are presented in leap interval were found to be different for the three real time on a commercial TV monitor, filling each living subjects (0–5 semitones for the female, 5–10, video frame from top to bottom. The system makes it 10–17 for the two males, respectively). These possible to observe left-right asymmetries, open differences are considered to reflect different quotient, propagation of mucosal waves, movement biomechanical properties of the vocal folds of the of the upper and, in the closing phase, the lower subjects examined. A small magnitude of the leap margins of the vocal folds, etc. The technique is found interval was associated with a smooth chest-falsetto suitable for further processing and quantification of transition in the female subject. recorded vibration. Chapter 5 investigates the resonance frequencies Chapter 7 demonstrates the potential of video- and the resonance modes of vibration of the vocal kymography to serve as a useful tool for a more detailed folds (of the same male subject as studied in chapters diagnostics of voice disorders. In the first part, 2 and 3). A novel method for laryngoscopic stroboscopic images of a male subject without a voice investigation of resonance properties of living vocal disorder are compared with the recorded video- folds is introduced here. Laryngeal vibrations were kymographic images. In the second part, the paper excited via a shaker placed on the neck of the subject introduces first videokymographic results obtained and observed by means of videostroboscopy and from patients with voice disorders. The video- videokymography. When the vocal folds were tuned kymographic images are shown side by side with to the phonatory frequency of 110 Hz and sinusoidal laryngoscopic and stroboscopic images in order to vibration with sweeping frequency (in the range 50 - summarize the essential anatomic, physiologic/ 400 Hz) was delivered to the larynx, three clearly pathologic and dynamic features of the vocal folds in pronounced resonance peaks (at frequencies around various voice disorders (unilateral vocal fold paralysis, 110, 170 and 240 Hz) were identified in the vocal fold chronic edema of the vocal folds, vocal fold polyp, tissues. The ratio of the first two resonance frequencies state after partial cordectomy right). It is shown that Švec: On Vibration Properties of Human Vocal Folds 117 videokymography makes it possible to observe all kinds patients with voice disorders (glottal hyperadduction, of vocal-fold vibrations, including those leading to sulcus glottidis, scarred vocal folds with ankylosis, pathological rough, breathy, hoarse, or diplophonic ventricular voice) and are documented by means of voice quality. The possibility of assessment of small sets of combined laryngoscopic, laryngostroboscopic left-right asymmetries, open quotient differences along and videokymographic images. the glottis, lateral propagation of mucosal waves, and Chapter 10 shows how videokymography can be movements of the upper and lower margins of the helpful in providing more detailed information on the vocal folds is advantageous for a more accurate phenomena related to chest-falsetto transitions. The diagnosis of voice disorders. changes of the vibratory pattern of the vocal folds Chapter 8 addresses the variability of vibration of during the chest-falsetto jumps as well as during the normal vocal folds as seen in videokymography. The formation of a subharmonic phonation are variability of the videokymographic findings depends documented here in detail and provided as an on (a) the measurement position and (b) the changes additional information on the phenomena studied in in voice quality. It is important to realize that the Chapters 2 – 4. It is noted that the 3:2 ratio has been measuring position is an essential factor here. It should observed to be associated with the magnitude of the be checked at which position along glottal length the chest-falsetto leap interval, with the two lowest measurement is taken, as well as whether the glottal resonance frequencies of the vocal folds as well as axis is perpendicular to the measuring line. The voice with the production of the subharmonic vibratory qualities such as loudness, pitch, type of phonation, or pattern in the particular subject. Videokymographic voice register are closely related to the vibratory and stroboscopic images of the behavior of the vocal pattern of the vocal folds. In some cases, the vibration folds in a patient suffering from mutational voice of normal vocal folds may become irregular (such as disorder are shown here which suggest that the x-2 in vocal fry, breathy voice, or coughing). As normal mode (characterized by lateral-medial oscillations with larynges are rarely ideally symmetric, one can often two half-wavelengths along the glottal length) might observe some degree of phase delay of one vocal fold play a role in production of involuntary frequency with respect to the second one. Under extreme jumps in some subjects. More experiments are needed conditions (as, e.g., high pitch or intensity) the in order to confirm these results in a larger amount of vibrations of the two vocal folds can also get subjects. desynchronized, imitating pathologic findings. Overall, videokymography provides detailed Understanding better the variability of the vibration information on vibration properties of the vocal folds of normal vocal fold should improve our ability to which proved helpful in explaining phenomena such recognize and distinguish various abnormalities and as register transitions. In clinical practice, the method pathologies. provides more detailed information on voice disorders Chapter 9 provides a review and the state of the art and considerably enriches laryngostroboscopy. There of videokymography in 1999. It compiles the research is no problem for videokymography to evaluate hoarse results achieved since the development of the method or unstable voice in which laryngostroboscopy fails. in 1994. The chapter is intended to serve as Also, the method is able to reveal structural a comprehensive introduction of the videokymographic irregularities on the medial surface of the vocal fold method to specialists interested in clinical examination (e.g., sulcus glottidis) which can easily be overlooked of voice. Characteristic features of the vocal-fold in laryngostroboscopy. Combination of a few vibration are illustrated and it is shown how they are laryngostroboscopic and videokymographic images can alternatively visualized in laryngostroboscopy and shortly and efficiently summarize important videokymography. Clinical value of the method is anatomical, physiological/pathological and vibration demonstrated by examples of laryngeal findings in properties of the laryngeal tissues in various patients.

Samenvatting en Conclusies

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SAMENVATTING EN CONCLUSIES

In Hoofdstuk 1 wordt het onderwerp van deze De Hoofdstukken 2–5 vormen het eerste deel van dissertatie geïntroduceerd waarbij de twee het proefschrift en behandelen de problemen die belangrijkste doelen worden aangegeven: (a) het geeft samenhangen met frequentieveranderingen tijdens de nieuwe informatie over fenomenen die samenhangen overgang van borststem naar falsetstem en de met de overgang van de borststem naar falsetstem, dynamische kenmerken van de stemplooien. beiden registers van de zangstem en (b) de ontwik- In Hoofdstuk 2 wordt een speciale stemmanoeuvre keling van een nieuwe, goedkope methode die meer geïntroduceerd om bij proefpersonen een abrupte gedetailleerde informatie geeft over het trillingsgedrag borststem-falsetstemovergang op te roepen. Een van de stemplooien. analogon met het “overblazen van een fluit” diende Het probleem van de stemregisters is een erg als model voor het produceren van de register- belangrijk, maar sterk controversieel onderwerp in de sprongen. De proefpersoon begint te foneren op een fysiologie van de zangstem en is nog niet volledig comfortabele geluidssterkte in borststemregister en opgelost. Het eerste deel van het proefschrift besteedt houdt de toonhoogte constant, terwijl geleidelijk de speciaal aandacht aan één aspect van het probleem uitgaande luchtstroom toeneemt. Deze manoeuvre van het stemregister, de plotselinge veranderingen in resulteerde in een spontane, abrupte verandering van het trillen van de stemplooien die vaak spontaan en de grondfrequentie van de stem. Deze manoeuvre onwillekeurig gebeuren tijdens de overgang van werd gedaan over het hele bereik van de borststem (ook wel modaal register genoemd) naar de grondfrequentie van een mannelijke proefpersoon falsetstem (borststem-falsetstemsprongen). Een zonder stemafwijkingen en het effect op de grond- experimentele benadering is hier gebruikt om nieuwe frequentie van de stem werd geanalyseerd. informatie te verkrijgen over deze stemverschijnselen. De waargenomen effecten verschilden in drie Sprongen van borststem naar falsetstem worden gebieden van de stem: (1) In het gebied van de lage geïnterpreteerd als bifurcaties, dit zijn verschijnselen frequenties (110–165 Hz, toonhoogten A2-E3, in de bekend uit de theorie van nietlineaire dynamica. Nederlandse notatieconventie: A-groot tot e-klein) Belangrijk inzicht belooft te worden verkregen door leidden veranderingen vanuit het borststemregister het identificeren van de manier van trillen van de tot een onregelmatige, perceptueel rauwe stem. In dit stemplooien (eigenmodes) die het uiteindelijke gebied werd de vorming gemeten van een toon met trillingspatroon van de stemplooien bepalen. Tot nu een F0/2 – frequentie, een subharmonische frequentie ontbreekt het aan gegevens over deze belangrijke (een octaaf lager klinkend dan de oorspronkelijk toon). eigenmodes van de stemplooien. Dit proefschrift levert (2) In het gebied van de midden-grondfrequenties (165- nieuwe gegevens over deze eigenmodes en eigen- 400 Hz, toonhoogten E3-G4, in de Nederlandse frequenties van de stemplooien in vivo. Ze zijn gemeten notatieconventie: e-klein tot g-ééngestreept) resul- en gevisualiseerd als resonantiefrequenties an reso- teerde de manoeuvre in sprongen van borststem- in nantiemodes. het falsetstemregister. De grootte van de toonhoog- Informatie over stemplooitrillingen werd teverandering bleek ongeveer zeven semitonen te zijn belemmerd als gevolg van de moeilijkheden bij het (een muzikaal interval van een kwint), gemeten bij de routinematig gebruik van laryngologische metho- startfrequentie van 165 Hz (E3). Het interval van dieken, zoals laryngovideostroboscopie bij het zeven semitonen kwam overeen met een registreren van onregelmatige trillingen van het frequentieverhouding van 3:2 (waarbij de beide uiteindelijke trillingspatroon enerzijds en ook door grondfrequenties met elkaar worden gerelateerd, de praktische onbereikbaarheid van de erg krachtige, respectievelijk na en voor de sprong). Met het stijgen maar zeer dure hoogfrequente beeldsystemen aan de van de begin-grondfrequentie, nam de grootte van de anderzijds. Een goedkope methode was nodig om in sprong af in semitonen. (3) In het hoogste staat te zijn meer gedetailleerd onderzoek te doen, frequentiegebied (400-660 Hz, toonhoogten G4-E5, g- zowel voor de registerovergangen als de onregelmatige ééngestreept tot e-tweegestreept) kon alleen het trillingspatronen. Het tweede deel van het proefschrift falsetstemregister worden geproduceerd. is gewijd aan de ontwikkeling en toepassing van een In Hoofdstuk 3 wordt het F0/2 subharmonisch nieuwe methode voor het onderzoek van de trillingspatroon van de stemplooien dat was stemplooitrillingen, dat videokymografie wordt geobserveerd in het vorige hoofdstuk in detail genoemd. bestudeerd. Gelijktijdige metingen met elektro- 120 Samenvatting en Conclusies glottografie en fotoglottografie brachten twee spronginterval bleken verschillend te zijn voor de drie verschillende open fasen binnen een subharmonische proefpersonen (0–5 semitonen voor de vrouw, 5–10 cyclus aan het licht – een eerste korte met een en 10–17 voor de twee mannen). Deze verschillen eenvoudige vorm, de tweede langer met een “rimpel”. lijken de verschillende biomechanische eigenschappen Parameters als het grote open quotiënt (ca. 0,8) en de van de stemplooien van de proefpersonen te hoge luchtstroomwaarden (ca. 1000 cm3/s) representeren. Een klein spronginterval bleek verband onderscheidden de fonatie van het vocal fry (pulse) te houden met een geleidelijke borststem-falsetstem register. overgang bij de vrouw. Gebruikmakend van een elektronische verdeler om Hoofdstuk 5 beschrijft de resonantiefrequenties en de grondfrequentie te volgen, werd een methode de trillingsmodes van de stemplooien (van dezelfde ontwikkeld om de subharmonische trilling van de mannelijke proefpersoon als in de hoofdstukken 2 en stemplooien stroboscopisch te volgen. De 3). Een nieuwe methode voor het laryngoscopisch stroboscopische visualisatie onthulde dat de onderzoek van de resonantie-eigenschappen van stemplooien niet gedesynchroniseerd waren, maar een levende stemplooien wordt hier geïntroduceerd. complex symmetrisch trillingspatroon vertoonden. Een Trillingen van het strottenhoofd werden met een ongebruikelijke beweging van het slijmvlies werd uitwendige vibrator op de hals van een proefpersoon gezien tijdens de “rimpel”: het werd gekarakteriseerd geïnduceerd en met videostroboscopie en video- door een openingsbeweging van de bovenste kymografie geobserveerd. Wanneer de stemplooien stemplooiranden die de sluitende beweging van de werden afgesteld op een fonatiefrequentie van 110 Hz stemplooien onderbraken. Als verklaring werd gegeven en een sinusoidale trilling met een veranderende dat dit trillingspatroon ontstond ten gevolge van frequentie over een bereik van 50–400 Hz aan de ontstemmen (detunen) van de gebruikelijk identieke larynx werd opgelegd, konden drie duidelijke frequenties van de dominante modes van de resonantiepieken (op frequenties van 110, 170 en stemplooien, waarbij het normale 1:1 patroon wordt 240 Hz) worden vastgesteld in het weefsel van de vervangen door een 3:2 entrainment. stemplooien. De verhouding van de eerste twee Hoofdstuk 4 keert terug naar de fenomenen van de resonantiefrequentie lag dicht bij de 3:2 verhouding borststem-falsetstemsprongen, die in detail bestudeerd die als sprongverhouding was vastgesteld tussen de zijn aan een geëxcideerde menselijke larynx en bij borststem-falsetstemsprong in hoofdstuk 2. drie proefpersonen (een vrouw en twee mannen). Het Verschillende resonantiemodes van de trillingen hoofdstuk biedt een nieuw concept over het van de stemplooien (gezien als duidelijke trillingen mechanisme van de abrupte borststem-falsetstem van lateraal tot mediaal met respectievelijk één, twee registerovergangen, gebaseerd op de bifurcatie- en drie halve golflengten langs de glottislengte, hangen effecten bekend van de theorie van de nietlineaire samen met deze resonantiefrequenties. Verondersteld dynamica. Gegevens van de geëxcideerde larynx lieten wordt dat de gelijktijdige excitatie van deze trillings- zien dat een kleine en geleidelijke verandering in de modes het complexe F0/2 (dat een octaaf lager klinkt lengtespanning in de stemplooien een abrupte dan de oorspronkelijke toon) subharmonische verandering van toonhoogte en register kan trillingspatroon kan produceren dat werd vastgesteld veroorzaken. Dit levert een bewijs dat de register- in Hoofdstuk 3. Behalve de stemplooien reageerden sprongen manifestaties zijn van bifurcaties in het ook andere laryngeale structuren op deze extern trillingspatroon van de stemplooien. Er werd een aangebrachte trilling. Onder de 100 Hz waren trillingen hysteresis vastgesteld; de opwaartse registersprong van de valse stemplooien (met een resonan- gebeurde bij hogere toonhoogten en spanningen dan tiefrequentie van ca. 70 Hz), de aryepiglottische de neerwaartse sprong. Als gevolg van deze hysteresis plooien en de bekerkraakbeentjes in de larynx kunnen de borststem- en falsetstemregisters binnen dominant. een bepaalde range van lengtespanningen in de De Hoofdstukken 6–9 vormen het tweede deel van stemplooien worden geproduceerd met praktisch deze dissertatie, gewijd aan de ontwikkeling en identieke laryngeale instellingen. toepassing van een nieuwe methode voor het De grootte van de frequentiesprong werd gemeten onderzoek van de trillingen van de stemplooien. als de sprongverhouding F0F : F0C (de grondfrequentie In Hoofdstuk 6 wordt een digitale techniek van het falsetstemregister in verhouding tot dat van geïntroduceerd voor high-speed visualisatie van de het borststemregister) en ook uitgedrukt in het trillingen van de stemplooien, videokymografie corresponderende muzikale interval, wat het genaamd, dat werd ontwikkeld en toegepast op de spronginterval wordt genoemd. De ranges van dit stemplooitrillingen. Het systeem gebruikt een Švec: On Vibration Properties of Human Vocal Folds 121 gemodificeerde videocamera die kan werken in twee registrerende lijn. Stemkwaliteiten als geluidssterkte, standen: een high-speed (bijna 8000 lijnbeelden per toonhoogte, fonatietype of stemregister staan in nauwe seconde) en de standaardstand (50 beeldjes per relatie tot het trillingspatroon van de stemplooien. In seconde in CCIR/PAL norm). In de high-speedstand sommige gevallen kan het trillingspatroon veranderen wordt met de camera een horizontale lijn (dwars op van een normaal in een onregelmatig patroon (zoals het beeld van de glottis) geselecteerd uit het hele in vocal fry, bij heesheid of bij hoesten). Aangezien laryngeale beeld. De op elkaar volgende lijnbeelden normale strottenhoofden zelden ideaal symmetrisch worden real-time weergegeven op een commercieel zijn, kan men vaak een bepaalde mate van verkrijgbare TV-monitor, waarbij iedere lijn van boven faseverschuiving zien van de ene stemplooi tot de naar beneden wordt afgebeeld. Het systeem stelt ons andere. Onder extreme omstandigheden (zoals in staat om een links-rechts asymmetrie, open quotiënt, bijvoorbeeld een hoge toon of geluidssterkte) kunnen voortplanting van de slijmvliesgolven, bewegingen van de twee stemplooien gedesynchroniseerd raken, de bovenranden, en in de sluitingsfase, de onderste waardoor pathologische omstandigheden worden randen van de stemplooien, enz., te observeren. De nagebootst. Het beter begrijpen van de variabiliteit techniek is geschikt bevonden voor verder bewerken van de stemplooitrillingen moet ons in staat stellen en kwantificeren van een opgenomen trilling. om verschillende abnormaliteiten and pathologische In Hoofdstuk 7 worden de mogelijkheden van toestanden te herkennen en van elkaar te videokymografie aangetoond als een bruikbaar onderscheiden. instrument voor gedetailleerder diagnostiek van Hoofdstuk 9 geeft een overzicht en beschrijft de stemstoornissen. In het eerste deel worden stand van zaken bij videokymografie in 1999. Het vat stroboscopische beelden van een mannelijk het onderzoek samen wat tot nu gedaan is sinds de proefpersoon zonder stemstoornis vergeleken met de ontwikkeling van de methodiek in 1994. Het hoofdstuk geregistreerde videokymografische beelden. Het is bedoeld als een begrijpelijke inleiding in de tweede deel geeft de eerste videokymografische videokymografische methodiek voor specialisten die beelden die verkregen zijn bij stempatiënten. De geïnteresseerd zijn in klinisch stemonderzoek. videokymografische beelden worden afgebeeld naast Kenmerken van de stemplooitrillingen worden de laryngoscopische en stroboscopische beelden om geïllustreerd en getoond wordt hoe de beelden van de de essentiële anatomische, fysiologische/pathologische trillingen worden weergegeven bij larynxstroboscopie en dynamische kenmerken van de stemplooien bij en bij videokymografie. De klinische waarde van de verscheidene stemstoornissen (unilaterale larynx- methode wordt gedemonstreerd aan de hand van helftverlamming, chronische oedeem van de voorbeelden van de bevindingen bij patiënten met stemplooien, stemplooipoliep, toestand na partiële stemstoornissen (glottische hyperadductie, sulcus chordectomie rechts) samen te vatten. Aangetoond glottidis, verlittekende stemplooien met ankylose van wordt dat het met videokymografie mogelijk is allerlei de arytenoidgewrichten, valse stemplooistem). De soorten stemplooitrillingen, inclusief die welke leiden afwijkingen worden gedocumenteerd door combinaties tot een pathologische rauwe, hese, schorre of diplofone van laryngoscopische, stroboscopische en video- stemklank te observeren. De mogelijkheid om kleine kymografische beelden. links-rechts asymmetrieën, verschillen in open quotiënt Hoofdstuk 10 toont hoe videokymografie kan over de lengte van de glottis, het naar lateraal gaan helpen om meer gedetailleerde informatie te verkrijgen van het stemplooislijmvlies en bewegingen van de over fenomenen die samenhangen met borststem- bovenste en onderste randen van de stemplooien vast falsetstemovergangen. De veranderingen in het te stellen is een voordeel voor een nauwkeuriger trillingspatroon van de stemplooien tijdens de diagnostiek van stemstoornissen. borststem-falsetstemsprongen en tijdens de vorming In Hoofdstuk 8 wordt de variabiliteit in van een subharmonische worden hier in detail stemplooitrillingen besproken zoals dat gezien wordt gepresenteerd. Ze geven aanvullende informatie over bij videokymografie. De variatie in de video- de verschijnselen zoals die bestudeerd zijn in hoofdstuk kymografische beelden hangt af van (a) de plaats van 2, 3 en 4. Vastgesteld wordt dat de 3:2 verhouding die de meting en (b) de veranderingen in stemkwaliteit. met de grootte van de borststem-falsetstemsprong Het is van belang te vast te stellen dat de meetplaats samenhangt, ook in verband gebracht kan worden hierin een essentiële factor is. Gecontroleerd moet met de laagste twee resonantiefrequenties van de worden op welke plaats langs de glottislengte het stemplooien en met de vorming van het sub- videokymogram wordt geregistreerd. En ook of de harmonische trillingspatroon bij dezelfde proef- lengte-as van de glottis loodrecht staat op de persoon. Videokymografische en stroboscopische 122 Samenvatting en Conclusies beelden van het gedrag van de stemplooien van een gedetailleerder informatie bij stemstoornissen en patiënt met een mutatiestoornis worden gegeven die verrijkt aanzienlijk de larynxstroboscopie. Schorre en suggereren dat de x-2 mode (gekenmerkt door lateraal- onstabiele stemmen kunnen worden onderzocht met mediale trillingen van twee halve golflengten langs de videokymografie, waar larynxstroboscopie faalt. Ook lengte van de glottis) een rol kan spelen bij het ontstaan kan met de methode structurele onregelmatigheden van de onwillekeurige frequentiesprongen bij sommige aangetoond worden op het mediale oppervlak van de personen. Meer experimenten zullen worden gedaan stemplooien, (bijvoorbeeld: sulcus glottidis), die om deze resultaten te bevestigen bij een groter aantal gemakkelijk met stroboscopie over het hoofd gezien proefpersonen. kunnen worden. Met het combineren van een paar Samenvattend kan worden gezegd dat video- larynxstroboscopische en videokymografische beelden kymografie gedetailleerde informatie verschaft over kan kort en efficiënt de belangrijkste anatomische, de trillingseigenschappen van de stemplooien, die fysiologische/pathologische en dynamische eigen- bewezen hebben dat ze van belang zijn in het schappen van laryngeaal weefsel bij uiteenlopende onderzoek naar verschijnselen zoals registerover- patiënten worden samengevat. gangen. In de klinische praktijk geeft de methodiek Acknowledgments Curriculum Vitae List of Publications

Acknowledgments

Švec: On Vibration Properties of Human Vocal Folds 125

ACKNOWLEDGMENTS

The research has been financially supported by a number of foundations and research projects (listed according to the year in which the support was provided):

• Civic Forum Foundation, which provided the author with a free-of-interest loan of 2000 USD for the stay at the Groningen Voice Research Lab, University of Groningen, the Netherlands in January-July 1993

• Jan Patočka Foundation, which provided the author with a three-month fellowship for the stay at the Groningen Voice Research Lab in January-March 1993

• Hlávka Foundation, which partially financially supported the stay of the author at the Groningen Voice Research Lab in April-July 1993

• Centre for Biomedical Technology (later Department of Biomedical Technology, Artificial Organs, recently Department of Biomedical Engineering), which financed the stay of the author at the University of Groningen in January-April 1994 (special thanks belong to Dr. G. Rakhorst and Dr. ir. G. J. Verkerke)

• TEMPUS JEP 1941, a joint European program, which provided the author a six-month fellowship for the stay at the University of Groningen in April-November 1994

• Czech Literary Fund, which partially financially supported the author’s research stay at the Groningen Voice Research Lab in April-May 1995

• Fulbright Commission of the Czech Republic awarded the author a “Travel Only Grant” which enabled presentation of the research results at the Voice Foundation’s symposium in Philadelphia in June 1995

• EUREKA Project EU 723 “Artificial Larynx” (1996–1999); via this project it became possible to start the research at the Center for Communication Disorders, Medical Healthcom in Prague, to continue the collaboration with the University of Groningen and to widely publish the research results at international congresses and symposia

• Project of the Grant Agency of Czech Republic GA ČR 106/98/K019 “Mathematical and Physical Modeling of Vibroacoustic Systems in Voice and Hearing Biomechanics,” which has been financially supporting the research since 1998

Special acknowledgment is expressed to:

• Lambert Instruments BV company (Leutingewolde, the Netherlands) for the technical realization of the videokymographic system

• Kay Elemetrics Corp (Lincoln Park, NJ, USA) for the support and stimulation of further research in videokymography 126 Acknowledgments

Personal thanks belong to:

• Prof. Dr. Harm K. Schutte, director of the Groningen Voice Research Lab who invited me to come for a research stay to the Groningen Voice Research Lab in 1993 and became the supervisor of my research. He has provided me with wide opportunities for experimental research, supervised the development of videokymography, supported my stays in Groningen and significantly influenced the start of my professional career as a voice scientist

• Ass. Prof. Dr. František Šram, director of the Centre for Communication Disorders, Medical Healthcom in Prague, the Czech republic, who enabled me to continue with the research in my home country. He created a laboratory in the Centre for Communication Disorders in Prague, specially suited to fit the needs of our research, and supported my efforts in every possible way. He became the first clinician who started to use videokymography in clinical practice; all the pathological images shown in this dissertation were derived from his clinical examinations

• Donald G. Miller, for our long-lasting discussions in the very beginning of my stay in the Netherlands which enabled me to find out what the current state of knowledge in the field of research on singing voice is. He has contributed to the research on voice registers presented in the dissertation and has been extremely helpful with improving my knowledge of English

• Prof. Dr. Ronald J. Baken, for valuable discussions and comments on my work, his personal support and guidance during my visits to the USA

• Ass. Prof. Dr. Josef Pešák, my first teacher who introduced me to the scientific subject of human voice and who helped me with the research activities at the Palacký University in Olomouc, Czech Republic

• Hana, my patient wife and distinguished mouse-clicker

• many others, who directly or indirectly helped me and stimulated my efforts Curriculum Vitae

Švec: On Vibration Properties of Human Vocal Folds 127

CURRICULUM VITAE Jan Švec born on November 22, 1966 in Olomouc, the Czech Republic

EDUCATION AND WORKING EXPERIENCE: Since November 1995: Medical Healthcom, Ltd., Centre for Communication Disorders, Prague, Czech Republic (Head: Ass.Prof. Dr. F. Šram). Voice scientist. 1995–99 (November-March): Department of Phoniatrics and Audiology, Institute for Postgraduate Medical Education, Prague (Head: Ass.Prof. Dr. F. Šram). Assistant of professor. 1990–96 Department of Experimental Physics, Palacký University, Olomouc, Czech Republic. Postgraduate studies in biophysics. Maj. subject: voice physiology (guided by Prof. Dr. J. Pospíšil and Dr. J. Pešák). Thesis “Studies of the Mechanical-Acoustical Properties of the Human Voice Source” defended on December 6, 1996. 1995 (April-May): Groningen Voice Research Lab, University of Groningen, the Netherlands. Short-time research stay in voice physiology (guided by Prof. Dr. H.K. Schutte). 1994 (April-November): Groningen Voice Research Lab, University of Groningen, the Netherlands. Doctoral studies and research in voice physiology (guided by Prof. Dr. H.K. Schutte). 1994 (January-April): Centre for Biomedical Technology, University of Groningen, the Netherlands. Research and development of techniques for visualization and quantification of vocal fold movement. 1993 (January-July): Groningen Voice Research Lab, University of Groningen, the Netherlands. Doctoral studies and research in voice physiology (guided by Prof. Dr. H.K. Schutte). 1985–90 Palacký University, Olomouc. M.Sc. studies (physics). Major subject: fine mechanics and optics. Minor subject: physiological acoustics. 1980–85 Gymnasium Hejčín, Olomouc.

Awards: 1997: The Best Scientific Video (silver medal) - AVEC World Video Festival of the XVI. World Congress of Otorhinolaryngology Head and Neck Surgery, Sydney, Australia, March 2–7, 1997 (for video program Švec JG, Schutte HK, Šram F: Introduction to Videokymography). 1996: Club of Alumni and Friends of the Palacký University in Olomouc — Extraordinary Award for doctoral scientific work [for publication Švec JG, Schutte HK, Miller DG: A Subharmonic Vibratory Pattern in Normal Vocal Folds. Journal of Speech and Hearing Research 1996; 39(1): 135–143]. 1995: Fulbright Commission Award (Travel Only Grant for presentation at the Voice Foundation’s symposium in Philadelphia). 1990: Rector’s Prize for results in studying, Palacký University, Olomouc.

INVENTIONS: Designer of “videokymography,” a method for optical high-speed observation of vibrations

EXTRACURRICULAR ACTIVITIES: 1983–92 Musician (composer, singer, guitar player, harmonica player) in the acoustic-jazz group PIANO. Published records: CD/LP/MC Piano (Piano, 1991; PI 0001-2 311); Compilations: LP Porta 1990 (Porta, 1990; C1 0002-1 311) LP/MC Porta ’89 (Supraphon 1989; 11 0415-1 311) Awards: 1989: Winners of the Czechoslovak national folk & country competition “PORTA 1989”. 1988 and 1989: Winners of the Czech national competition of music groups “Academic Prague”. List of publications of the author

128 Curriculum Vitae

PUBLICATIONS: 2. Švec J.: Studium mechanicko-akustických vlastností zdroje lidského hlasu. [Studies of the Mechanical-Acoustical Scientific journals: Properties of the Human Voice Source]. (Dissertation, in 1. Švec J., Pešák J.: Vlastnosti hlasových přeskoků. Czech). Faculty of Natural Sciences, Palacký University, [Properties of Voice Breaks]. (In Czech). Bulletin of the Olomouc, the Czech Republic (1996). Acoustical Society of Czechoslovakia 2/1992: 1–5 (1992). 2. Pešák J., Švec J.: Intralaryngeal Pressure Conditions Video program: and a Membranophonic Interpretation of Voice 1. Švec J. G., Schutte H. K., Šram F.: Introduction to Production. Folia Phoniatrica, 45: 90–95 (1993) Videokymography. (An instructional videofilm). Centre 3. Švec J., Pešák J.: Vocal Breaks from the Modal to Falsetto for Communication Disorders and Groningen Voice Register. Folia Phoniatrica et Logopaedica, 46: 97–103 Research Lab, Prague and Groningen. Produced by (1994). Medical Healthcom, Ltd., Prague (1997). 4. Schutte H. K., Miller D. G., Švec J. G.: Measurement of Formant Frequencies and Bandwidths in Singing. Journal Chapters in Proceedings: of Voice, 9(3): 290–296 (1995). 1. Švec J. G., Schutte H. K.: High-Speed Line-Scanning 5. Švec J. G., Schutte H. K., Miller D. G.: A Subharmonic Technique for Investigation of Vocal Fold Vibration / Vibratory Pattern in Normal Vocal Folds. Journal of Videokymography/. In Melka A., Otčenášek Z., Štěpánek Speech and Hearing Research, 39(1): 135–143 (1996). J. (Eds): Proceedings of the 32nd Czech Conference on 6. Švec JG, Schutte HK: Videokymography: High–Speed Acoustics, SPEECH – MUSIC – HEARING, Prague, Line Scanning of Vocal Fold Vibration. Journal of Voice, September 23–26, 1995. Česká akustická společnost, 10(2): 201–205 (1996). Praha: 71–74 (1995). 7. Schutte H. K., Švec J. G., Šram F.: Videokymography: 2. Schutte H. K., Švec J. G., Šram F.: Videokymography – Research and Clinical Issues. Logopedics, Phoniatrics, a Modern Imaging System for Analyzing Regular and Vocology, 22(4): 152–156 (1997). Irregular Vibrations. In Gross M, Eysholdt U (Eds): 8. Schutte H. K., Švec J. G., Šram F.: First Results of Aktuelle phoniatrisch-pädaudiologische Aspekte 1996, vol. Clinical Application of Videokymography. Laryngoscope, 4. Verlag Abteilung Phoniatrie, Göttingen: 272–274 108: 1206–1210 (1998). (1997). 9. Švec J. G., Schutte H. K.: Videokymography: High– 3. Švec J. G., Schutte H. K., Šram F.: Videokymography: Speed Line Scanning of Vocal Fold Vibration. Bulletin High-Speed Line Scanning of Vocal Fold Vibration. In d’ Audiophonologie – Ann. Sc. Univ. Fr. – C., XV(1): 9– McCafferty G., Coman W., Carroll R. (Eds.): Proceedings 18 (1999). of the XVI World Congress of Otorhinolaryngology, Head 10. Švec J. G., Šram F., Schutte H. K.: Videokymografie: and Neck Surgery, Sydney, Australia, March 2–7, 1997. nová vysokofrekvenční metoda vyšetřování kmitů Monduzzi Editore, Bologna [ISBN: 88-323-0302-7]: hlasivek. [Videokymography: a New High-Speed Method 1685–1688 (1997). for the Examination of Vocal–Fold Vibrations] (In 4. Schutte H. K., Švec J. G., Šram F.: Videokymography – Czech). Otorinolaryngologie a foniatrie (Prague), 48(3): Imaging and Quantification of Regular and Irregular 155–162 (1999). Vocal Fold Vibrations. In McCafferty G, Coman W, 11. Švec J. G., Schutte H. K., Miller D. G.: On Pitch Jumps Carroll R (Eds.): Proceedings of the XVI World Congress Between Chest and Falsetto Registers in Voice: Data of Otorhinolaryngology, Head and Neck Surgery, Sydney, from Living and Excised Human Larynges. Journal of Australia, March 2–7, 1997. Monduzzi Editore, Bologna the Acoustical Society of America, 106(3): 1523–1531 [ISBN: 88-323-0302-7]: 1739–1742 (1997). (1999). 5. Šram F., Schutte H. K., Švec J. G.: Clinical Applications 12. Pellant A., Chrobok V., Šram F., Švec J.: Naše zkušenosti of Videokymography. In McCafferty G, Coman W, s tyreoplastikou typ I. [Our Experience with Thyroplasty Carroll R (Eds.): Proceedings of the XVI World Congress Type I]. (In Czech). Otorinolaryngologie a foniatrie of Otorhinolaryngology, Head and Neck Surgery, Sydney, (Prague), 48(4): 222–226 (1999). Australia, March 2–7, 1997. Monduzzi Editore, Bologna 13. Švec J. G., Horáček J., Šram F., Veselý J.: Resonance [ISBN: 88-323-0302-7]: 1681–1684 (1997). Properties of the Vocal Folds: In Vivo Laryngoscopic 6. Dedouch, K., Vohradník M., Laub M., Švec J.: Návrh Investigation of the Externally Excited Laryngeal ortotropního modelu hlasivky. [Finite element model of Vibrations. Journal of the Acoustical Society of America vocal fold tissues with orthotropic material properties] (accepted for publication). (In Czech). In: Proceedings of the National Conference with International Participation ENGINEERING Theses: MECHANICS ’98, Svratka, the Czech Republic 11–14 1. Švec J.: Mechanismus rezonanční soustavy hlasového May 1998. Institute of Thermomechanics, Academy of ústrojí. [Mechanism of the resonance system of the human Sciences of the Czech Republic, Prague [ISBN 80-85918- voice]. (Master Thesis, in Czech). Department of Optics, 40-4]: 107–112 (1998). Faculty of Natural Sciences, Palacký University, 7. Švec J. G., Šram F., Schutte H. K.: Videokymografie: Olomouc, the Czech Republic (1990). nová metoda pro sledování kmitů hlasivek. Švec: On Vibration Properties of Human Vocal Folds 129

[Videokymography: A New Method for Investigation of Thermomechanics, Academy of Sciences of the Czech Vocal-Fold Vibration] (In Czech). In: Pešák J. (Ed.): Republic, Prague [ISBN: 80-85918-49-8]: 131–134 (1999). Sborník přednášek 1. semináře univerzitního Společenství 15. Dedouch K., Vampola T., Švec J.: Analýza vlivu délky pro studium hlasu a řeči. Group for Study of Voice and kmitající části hlasivky na změnu modálních vlastností Speech, Palacký University, Olomouc, the Czech hlasivky. [Influence of the length change on modal Republic: 11–14 (1999). properties of the vocal fold tissues] (In Czech). In: Křen 8. Dedouch K., Vohradník M., Laub M., Švec J.: Výpočetní J. (Ed.): 15th Conference with International Participation model hlasivky za patologického stavu. COMPUTATIONAL MECHANICS ’99, October 18–20, [A Computational Model of the Vocal Fold under 1999, Nečtiny, Czech Republic. University of West Pathologic Conditions] (In Czech). In: Jelen K., Pejšová Bohemia, Pilsen [ISBN: 80-7082-542-1]: 39–46 (1999). J. (Eds.): Biomechanika člověka ’98, VII. konference České 16. Dedouch K., Horáček J., Vampola T., Švec J.: Akustické společnosti pro biomechaniku: Proceedings. FTVS UK vlastnosti konečnoprvkového modelu vokálního traktu Praha [ISBN: 80-902147-9-7]: 19–22 (1999). člověka. [Acoustical characteristics of FE model of the 9. Švec J. G., Schutte H. K., Šram F.: Úvod do human vocal tract] (In Czech). In: Zolotarev I (Ed.): videokymografie. [Introduction to Videokymography] Sborník referátů semináře INTERAKCE A ZPĚTNÉ (In Czech). In: Jelen K., Pejšová J. (Eds.): Biomechanika VAZBY ’99. Ústav termomechaniky AV ČR, Praha člověka ’98, VII. konference České společnosti pro [ISBN: 80-85918-50-1]: 41–48 (1999). biomechaniku: Proceedings. FTVS UK Praha [ISBN: 17. Horáček J., Švec J. G.: Formulation of a mathematical 80-902147-9-7]: 231–234 (1999). model of vocal folds oscillations. In: Zolotarev I. (Ed.): 10. Švec J. G., Schutte H. K., Šram F.: Variability of Vibration Sborník referátů semináře INTERAKCE A ZPĚTNÉ of Normal Vocal Folds as Seen in Videokymography. In: VAZBY ’99. Ústav termomechaniky AV ČR, Praha Dejonckere P. H., Peters H. F. M. (Eds.): Communication [ISBN: 80-85918-50-1]: 57–64 (1999). and Its Disorders: A Science In Progress. Proceedings 24th 18. Šram F., Švec J. G.: Videokymografie v klinické praxi. Congress International Association of Logopedics and [Videokymography in Clinical Practice] (In Czech). In Phoniatrics, Amsterdam, the Netherlands, August 23–27, Pešák J. (Ed.): Sborník přednášek 5. semináře univerzitního 1998. Vol.I. International Association of Logopedics and Společenství pro studium hlasu a řeči. Group for Study of Phoniatrics [ISBN: 90 5710 071 1]: 122–125 (1999). Voice and Speech, Palacký University, Olomouc, the 11. Šram F., Švec J. G., Schutte H. K.: Possibilities for Use Czech Republic: 12–19 (2000). of Videokymography in Laryngologic and Phoniatric 19. Švec J. G., Šram F., Schutte H. K.: Videokymografie: Practice. In: Dejonckere P. H., Peters H. F. M. (Eds.): nová metoda pro sledování kmitů hlasivek. Communication and Its Disorders: A Science In Progress. [Videokymography: A New Method for Investigation of Proceedings 24th Congress International Association of Vocal-Fold Vibration] (In Czech). In: Pešák J. (Ed.): Logopedics and Phoniatrics, Amsterdam, the Netherlands, Psychotrofon 1: I. soubor přednášek. Palacký University, August 23–27, 1998. Vol. I. International Association of Olomouc, the Czech Republic [ISBN: 80-244-0074-X]: Logopedics and Phoniatrics [ISBN: 90 5710 071 1]: 256– 23–27 (2000). 259 (1999). 20. Šram F., Švec J. G.: Videokymografie v klinické praxi. 12. Mládková P., Kantová M., Šram F., Švec J.: Co-Operation [Videokymography in Clinical Practice] (In Czech). In of Specialists in the Treatment of Patients with Voice, Pešák J. (Ed.): Psychotrofon 1: I. soubor přednášek. Speech and Language Disorders and Hearing Palacký University, Olomouc, the Czech Republic [ISBN: Impairment. In: Dejonckere P. H., Peters H. F. M. (Eds.): 80-244-0074-X]: 28–36 (2000). Communication and Its Disorders: A Science In Progress. 21. Švec J. G., Šram F., Schutte H. K.: Videokymography in Proceedings 24th Congress International Association of 2000: the Present State and Perspectives of the High- Logopedics and Phoniatrics, Amsterdam, the Netherlands, Speed Line-Imaging Technique. In Braunschweig T., August 23–27, 1998. Vol. II. International Association of Hanson J., Schelhorn-Neise P., Witte H. (Eds.): Advances Logopedics and Phoniatrics [ISBN: 90 5710 071 1]: 970– in Quantitative Laryngoscopy, Voice and Speech Research. 972 (1999). Proceedings of the 4th International Workshop. Jena, April 13 Dedouch K., Vohradník M., Švec J.: Modální analýza 7–8, 2000. Friedrich-Schiller University, Jena, Germany výpočetního modelu hlasivky. [Modal analysis of the [ISBN: 3-00-005636-X]: 57–62 (2000). computational model of the vocal fold] (In Czech). In: 22. Šram F., Švec J. G.: Results of Videokymographic Kratochvíl C., Kotek V., Krejsa J. (Eds.): INŽENÝRSKÁ Examinations by Functional Voice Disorders. In: Gross MECHANIKA ’99, Svratka, 17.–20. května 1999. Sborník, M. (Ed.): Aktuelle phoniatrisch-pädaudiologische Aspekte svazek 1. Ústav mechaniky těles, Fakulta strojní, VUT 1998/1999: Stimme – Sprache – Schlucken – Hören. v Brně [ISBN: 80-214-1323-9]: 493–498 (1999). (in press) 14. Dedouch K., Horáček J., Vampola T., Vohradník M., 23. Šram F., Švec J. G.: Die Tonerzeugung beim Spielen von Švec J.: Finite Element Model of Supraglottal Vocal Blasinstrumenten (in press). Tract with Consideration of Wall Impedance. In Horáček 24. Dedouch K., Horáček J., Švec J.: Frequency modal J., Zolotarev I. (Eds.): Proceedings of the 3rd International analysis of supraglottal vocal tract (in press). Conference ENGINEERING AERO-HYDRO- ELASTICITY, Prague 1999. Institute of

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