STUDIES in VIBRATIONS CAUSING PULMONARY Ological Conditions

STUDIES IN VIBRATIONS CAUSING PULMONARY PHYSICAL SIGNS.

By CHARLES M. MONTGOMERY, M.D.,

PHILADELPHIA, PA. Those engaged in making physical examinations of the chest are constantly facing problems that are both interesting and baffling. Deserving of special mention are those concerned with the normal vocal resonance: why it possesses its peculiar characteristics; how it can exist over a lung that is silent to many vibrations such as those produced during the act of whispering; and why, under pathological conditions, whispering pectoriloquy and allied sounds become plainly audible even when the vocal resonance and fremitus become less intense than normal. An endeavor to throw light on some of these problems has resulted in the present paper, which claims to be little more than a preliminary report. Only brief allusion will be made to the considerable amount of experimental work that has con- tributed largely to the results presented. The recent literature adds little to our knowledge of these problems, and reference will only be made to a very suggestive article published in 1919 (Adams & Montgomery, Physical Signs and their Mechanism in Acute Pulmonary Inflammation, Jour. Amer. Med. Assoc., April 5, 1919). The various theories appearing from time to time dealing with the problems will not be discussed. THE VOCAL VIBRATIONS IN THE UPPER RESPIRATORY TRACT: During the act of speaking or singing, expiratory currents of air set into vibration the taut vocal cords. The cords, under these conditions, vibrate both throughout their entire length and also in seg- ments. These vocal cord vibrations are the vibrations originally responsible for the vocal sounds heard at the mouth and over the chest surface. The vibrations initiated by the vocal cords become markedly altered above the cords by various resonating chambers 89 90 CHARLES M. MONTGOMERY of the throat and head, some vibrations becoming much intensified, while others are much diminished or lost by the time actual audible vocal speech is produced. In addition, new sounds are added from the lips, teeth, etc. The resultant sound coming from the mouth is, therefore, far different from that originally produced by the vocal cords. In the respiratory passages below the cords some modifica- tions of the original vocal cord vibrations likewise occurs. These lower respiratory passages also transmit vibrations coming from above the vocal cords. THE VOCAL VIBRATIONS OVER THE NORMAL LUNG: These vibrations are markedly different from those coming from the open mouth and even from those heard over various portions of the neck, especially posteriorly. They are lower in pitch than articulate speech, muffled, distant, and in no way give a clue to the actual words as spoken. They may persist unchanged, independently of marked alterations in the character of audible speech. Various manipulations of the chambers of the upper respiratory tract causing marked changes in the sounds coming from the mouth have apparently little effect on the normal vocal resonance and vocal fremitus. Whether one employs, or eliminates, so striking a feature as the nasal element of speech seems to have little effect on the vibrations recognized at the chest surface. One is driven to believe that the respiratory tract above the vocal cords plays little part, except perhaps in the matter of intensity, in the production of normal vocal resonance and fremitus. This belief finds support in the fact that marked changes in the pitch of the vocal resonance can be effected by altering the pitch of the vibrations due directly to the vocal cords, the chambers of the upper respiratory passages remaining unchanged. Likewise, marked changes in the intensity of the vocal fremitus and resonance over the normal lung may be obtained by changing the condition of the vocal cords with the resultant changes in pitch of the vibrations produced by the cords. Thus in the same individual changing the pitch of the voice by vocal cord action will intensify the vocal fremitus and resonance over one area of the chest, while it decreases them in another, whereas, a different state of the vocal cords may produce just the opposite results. Available clinical evidence supported by experimental data indicates that the vibrations perceived over the normal lung as vocal resonance and vocal fremitus VIBRATIONS CAUSING PULMONARY SIGNS 91 are closely allied to those 'originally produced by the vocal cords. The respiratory chambers below the cords, and to a less extent perhaps those above the cords, contribute to the end result chiefly in affecting the intensity of the vibrations appearing at the chest surface. What part is played in this result by the vibrations of the cords as a whole, and what part by the segmental vibrations need further investigation. Vocal vibrations, if the above is correct, may be classified in two groups, whether listened to over the neck, chest, or elsewhere, first: those resembling the primary vocal cord vibrations in most of the important features, except intensity; and, secondly: all other ordinary vibrations, such as the important overtones produced during speech. Both groups are present in the upper respiratory tract as shown by listening over the neck, while only the former reach the chest surface under normal conditions. All vibrations recognized as vocal fremitus fall in the first group, that is, are due to the primary vocal cord vibrations However, these latter do not always yield vocal fremitus as is sometimes observed in the examination of chests of women and children. Not only do we fail to find many important elements of spoken speech absent over the normal lung, but other kinds of vibrations produced in the upper respiratory tract, for example, during whispering and breathing, reach the chest surface indistinctly, if at all, under normal conditions, while they are plainly audible over the neck. Whispering sounds and breathing sounds produced in the upper respiratory tract may then be classified with those vibrations produced during spoken vocalization which are not directly traceable to the vocal cords themselves, such vibrations, for example, as furnish the distinctive overtones in bronchophony. This group of vibrations does not yield fremitus. VIBRATIONS OVER THE SOLID LUNG OR SOLID LUNG SEPARATED FROM THE CHEST WALL BY FLUID: Under these conditions, vibrations may be perceived at the chest surface, resembling crudely those audible over the back of the neck, or even those coming from the mouth as speech, that is, all types of vibrations previously discussed may be recognized. Thus one obtains vocal cord vibrations much obscured by other elements of the spoken voice, and also breath and whispered sounds coming from the upper respiratory tract. It is 92 CHARLES M. MONTGOMERY observed also in these pathological conditions that while many sounds become audible that are normally absent, the relatively pure vocal cord vibrations may be less intense than normal as revealed by both palpation and ausculation, resulting in an actual diminution of vocal fremitus and resonance. It may be concluded, then, that when a lung is solid, different kinds of vibrations in the lower respiratory passages reach the chest surface with the same relative intensity as existed in those passages. The solid lung does not show any special action in favor of one kind of vibration over another kind. On the other hand, the normal lung reveals at its surface only those vibrations traceable directly to the vocal cords, to the exclusion of most or all of the others, and, indeed, these vocal cord vibrations may exceed in intensity the vocal cord vibrations heard and felt over the solid lung. Why this difference between normal. and solid lung? Appar- ently the solid lung does the ordinary and simple thing, while the peculiarities in the case rest with the normal lung, which appears to favor some vibrations while opposing others. The exclusion of some of the vibrations, like those due to whispering, in the case of the normal lung is to be attributed to the poor conditions for the transmission of vibrations existing between the walls of the air passages and the chest surface. That other vibrations readily reach the surface is believed to be due to the fact that the walls of these air passages are set into a peculiar degree of intensity of vibration by certain rhythmic or periodic vibrations such as are found in the original vocal cord vibrations during speaking or singing. This sort of phenomenon may be illustrated by the following simple example: A paper scroll or one end of a properly shaped, thin-walled, cardboard box is thrown into marked palpable and audible vibrations by the human voice during speaking or singing in a suitable way, the open mouth being separated a short distance by air from one of the openings in the paper scroll, or the single opening in the box. By properly connecting the exterior of either the scroll or box by a wire with the diaphragm of a Bowles' stethoscope, the vibrations are distinctly audible, possessing a muffled, humming sound not unlike the normal vocal resonance, and, like the latter, lacking the overtones and other peculiarities of speech. Moreover, whispering sounds produced under similar circumstances no matter VIBRATIONS CAUSING PULMONARY SIGNS 93 how loud, may yield little or no sound. It will be noted that in the case of the vocal cords and the lung, and in the case of the voice and the paper scroll, the medium of air separates the primary and secondary vibrating bodies. This phenomenon is a manifestation of what the physicists term "forced vibrations." Forced vibrations are set up in many different kinds of structures by proper primary or activating bodies of widely different pitch and quality, the pitch and quality in the secondary body corresponding to those of the primary vibrating body. The term "sympathic vibrations" on the other hand signifies that the secondard body thrown into vibration requires that the primary body vibrate at the pitch peculiar to the secondary body, that is, have the same vibration period, as when one tuning fork is set into vibration by another of the same pitch. The term "forced vibrations" is also applicable to cases where two solid bodies come in contact with each other without the intervention of air, as when a tuning fork applied to a piece of wood sets it into vibrations of its own period. Forced vibrations are also illustrated when a string of a violin sets the attached wooden frame into vibrations of its own period. The absence of such direct contact is illustrated very simply by holding the vibrating prongs of tuning forks varying considerably in pitch at, or inside, the opening to a thin paper box or other suitable structure, when distinct vibrations can be detected by the palpating hand. A point to be emphasized is that the results are not limited to tuning forks of a narrow range of pitch, and likewise with the human voice and chest, palpable vibrations exist with the vocal cords yielding quite a wide range of pitch. The normal vocal resonance is low in pitch not because the lungs favor transmsision of low pitched sounds, but because the vocal cords primarily produce vibrations of relatively low pitch. In the experiments illustrating the production of forced vibrations in a secondary body which is separated by a medium of air from the primary vibrating body, delicate and thin-walled structures are required in order to yield satisfactory results. With increased thickening and stiffness of these walls the energy of the forced vibrations decreases and finally disappears. Whatever vibrations enter thick and unyielding structures follow the ordinary laws gov- erning the passage of vibrations between media of different density. 94 CHARLES M. MONTGOMERY In the case of the normal lung, we find air passages with walls sufficiently delicate and yielding, and yet sufficiently tense, even fairly far up in the respiratory tract, to be readily set into vibration by the vocal cord vibrations, which, below the cords, are contained in closed spaces which offer thereby special advantages for preserving and even amplifying vibration energy. The cords apparently are capable of making forced vibrations possible by virtue of the relatively rhythmic or periodic nature of their vibrations which differ entirely, if we leave out the element of intensity, from whispering vibrations. The walls of the air passages are set into vibration in this way with sufficient energy for the vibrations to continue to the external chest surface despite the obstructive factors existing normally, factors which successfully obstruct all ordinary vibrations except this particular kind, factors which do not exist when the lung is solid. Just how much energy exists in the vibrations of the vocal cords themselves has not been determined, but it is sufficient in some people to throw the laryngeal walls into visible vibration. Moreover, the evidence indicates that this tube wall conduction of vibrations continues for a considerable distance down the trachea if not as far or further than the bifurcation. The phenomena described exist in the human subject entirely outside of the lungs. The vocal fremitus and resonance present over the nose furnish a good example of forced vibrations, these vibrations being practically eliminated by closing the posterior nares. Interference with this phenomenon is clearly revealed in those fairly numerous cases in which normally the vocal fremitus, and less fre- quently the vocal resonance are less over the back of the neck than over the chest wall. The neck back of the trachea acts on this part of the trachea much as consolidation affects the bronchial walls, making them thicker by embracing them with a solid material, so that they become less susceptible to yielding forced vibrations. Other areas exemplify the same thing to a more striking degree, for example, the temporal region just above the zygoma and in front of the ear, where very distinct whispering pectoriloquy may be obtained with little or no vocal fremitus and resonance. SUMMARY: From the evidence at hand, it appears that the normal vocal fremitus and resonance are traceable to, and closely VIBRATIONS CAUSING PULMONARY SIGNS 95 resemble, the primary vocal cord vibrations. These vibrations, by reason of their peculiar rhythmicity or periodicity, are capable of setting into forced vibrations certain susceptible structures such as the walls of parts of the normal respiratory passages, thereby endow- ing these walls with sufficient vibratory energy to overcome the natural obstacles offered to vibrations in their passage to the chest surface under normal conditions. Other vibrations lacking these peculiar qualities fail to set these tube walls into a state of sufficient vibratory energy for vibrations to be manifested at the chest surface. Over solid lung a much greater variety of vibrations coming from the respiratory passages reach the chest surface, for example, those found in whispering pectoriloquy, bronchial breathing, and bronchophony. When the lung is solid, conditions are more favorable for the simple conduction of vibrations than when it is normal. It does not offer conditions favorable to forced vibrations, but affects all vibrations much alike. DISCUSSION. DR. JUDSON DALAND, Philadelphia: I have been exceedingly interested in Dr. Montgomery's paper, and desire to occupy your attention to record a case reported by Dr. Porter of Buffalo, in which the anterior part of the chest was removed for empyema and you could look in and see the heart beating and see no lung there. He got excellent vocal fremitus on the side with no lung ir. contact with the chest except posteriorly. So I think that there must be another factor to be given consideration, namely, vibration of a coarse variety, transmitted through the lungs and out to the hands. DR. J. B. ELLIOT, Toronto: This contribution is interesting from the point of view of teaching physical diagnosis to students. You have difficulty in making students understand why certain phenomena occur in the physical examination of the chest. Dr. Montgomery says that the vibrations from the vocal cord are carried to the chest through the bronchial walls. I should like to know whether this is anything other than pure theory; because we understand that when carrying vibrations from of either sound or light, they are deflected if forced through tissues of different density. The bronchial wall is a tissue of great variations in density, composed of cartilage and softer and less dense tissue. Not only are these two tissues present, but they are alternating all the way down. This being the case, tissues of different density deflecting sound, it is difficult to tell how the bronchial walls will carry vibrations from the cord. It is a simple explanation to think that the sound is carried by the air column in the bronchial tree, rather than by the bronchial walls and it would help us in our teaching if these things could be settled. 96 DISCUSSION

DR. MONTGOMERY, closing: This is only a very small piece out of a large subject, and it is impossible to give anything like evidence in so short a time. With regard to Dr. Daland's case, I did not quite understand what he said about it. Was the lung separated from the chest wall by air? DR. DALAND: The lung was collapsed on a very old empyema. There was just a small portion of collapsed lung posteriorly. You could see it with the eye. Nevertheless, fremitus was present. DR. MONTGOMERY: In that case there was probably a solid lung, a small one, connected with the chest wall. DR. DALAND: You could look through the opening into the chest and see the whole thing. DR. MONTGOMERY: Where did you listen? DR. DALAND: I simply palpated. DR. MONTGOMERY: You palpated over air? DR. DALAND: No; on the chest at the side of the opening. DR. MONTGOMERY: If you palpated over the chest, you had air, if below, fluid. DR. DALAND: The opening was two inches and a half. You could look in and see the heart beating; and at the back, a substance that looked like an old collapsed lung. I came over to the front, where I could see underneath where my hand was, and could see that there was no lung there, and palpated and got well-marked vocal fremitus. DR. MONTGOMERY: That is interesting. I do not know how often you would get it under the conditions. There is no question of the great transmiss- ibility of bone, even when surrounded by the muscles. It is. You get pectoriloquy from the cavity, although in contact with solid tissue all the way through. DR. DALAND: It looks like a coarse bone transmission. DR. MONTGOMERY: Replying to Dr. Elliott's inquiry, I would say that I did not mean to state that the vibration was carried from the vocal cord down along the walls of the bronchial tree. I meant that they went from the vocal cords by the aerial route to the walls of the bronchi. You have a closed cavity, which multiplies the sound and increases it. That might take place high up on the bronchial tree. I do not know how far the vibrations are carried by direct conduction down the bronchial wall. Dr. Fetteroff -had a case and said that conduction was cut off. As you say, it is probably on the right track and is dampened by the solid tissue. It goes across the air. It is a case of forced vibration, entirely different from simple conduction.