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2-20-2014 Fundamentals of Abraham Bohadana Shaare Zedek Medical Center, Israel

Gabriel Izbicki Shaare Zedek Medical Center, Israel

Steve S. Kraman University of Kentucky, [email protected] Click here to let us know how access to this document benefits oy u.

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Repository Citation Bohadana, Abraham; Izbicki, Gabriel; and Kraman, Steve S., "Fundamentals of Lung Auscultation" (2014). Internal Medicine Faculty Publications. 61. https://uknowledge.uky.edu/internalmedicine_facpub/61

This Article is brought to you for free and open access by the Internal Medicine at UKnowledge. It has been accepted for inclusion in Internal Medicine Faculty Publications by an authorized administrator of UKnowledge. For more information, please contact [email protected]. Fundamentals of Lung Auscultation

Notes/Citation Information Published in The New England Journal of Medicine, v. 370, no. 8, p. 744-751.

From The New England Journal of Medicine, Abraham Bohadana, Gabriel Izbicki, and Steve S. Kraman, Fundamentals of Lung Auscultation, 370, 744-751. Copyright © 2014 Massachusetts eM dical Society. Reprinted with permission.

Digital Object Identifier (DOI) http://dx.doi.org/10.1056/NEJMra1302901

This article is available at UKnowledge: https://uknowledge.uky.edu/internalmedicine_facpub/61 The new england journal of medicine

review article

Edward W. Campion, M.D., Editor Fundamentals of Lung Auscultation

Abraham Bohadana, M.D., Gabriel Izbicki, M.D., and Steve S. Kraman, M.D.

From the Pulmonary Institute, Shaare ­Zedek hest auscultation has long been considered a useful part of Medical Center, and the Hebrew University the , going back to the time of Hippocrates. However, Hadassah Medical School, Jerusalem (A.B., G.I.); and the University of Kentucky School it did not become a widespread practice until the invention of the stetho- of Medicine, Lexington (S.S.K.). Address C 1 scope by René Laënnec in 1816, which made the practice convenient and hygienic. reprint requests to Dr. Bohadana at the Pul- During the second half of the 20th century, technological advances in ultrasonog- monary Institute, Shaare Zedek Medical Center, 12 Baiyt St., 91031 Jerusalem, Israel, raphy, radiographic computed tomography (CT), and magnetic resonance imaging or at [email protected]. shifted interest from lung auscultation to imaging studies, which can detect lung N Engl J Med 2014;370:744-51. with an accuracy never previously imagined. However, modern computer- DOI: 10.1056/NEJMra1302901 assisted techniques have also allowed precise recording and analysis of lung sounds, Copyright © 2014 Massachusetts Medical Society. prompting the correlation of acoustic indexes with measures of lung mechanics. This innovative, though still little used, approach has improved our knowledge of acoustic mechanisms and increased the clinical usefulness of auscultation. In this review, we present an overview of lung auscultation in the light of modern concepts of lung acoustics.

Nomenclature

The traditional nomenclature for lung sounds suffers from imprecision. Therefore, in this article, we have adopted the terminology proposed by the ad hoc committee of the International Lung Sounds Association.2 In this classification of lung sounds, the term “rale” is replaced by “crackle,” since the adjectives often used to qualify rales (e.g., “moist” or “dry”) can be misleading with regard to the means by which rales (or ) are produced. “Crackle” can be defined acoustically and does not suggest any means or site of generation. The clinical characteristics of normal and An ­interactive graphic is adventitious sounds are summarized in Table 1, and the lung sounds can be heard ­available at in an interactive graphic, available with the full text of this article at NEJM.org. NEJM.org Normal

Tracheal Sounds Tracheal auscultation is not frequently performed, but in certain situations it can convey important clinical information. When heard at the suprasternal notch or the lateral , normal tracheal sounds characteristically contain a large amount of sound energy and are easily heard during the two phases of the respiratory cycle (Fig. 1A). The frequencies of these sounds range from 100 Hz to almost 5000 Hz, with a sharp drop in power at a frequency of approximately 800 Hz and little energy beyond 1500 Hz.4 They are produced by turbulent airflow in the , glottis, and subglottic region. Listening to tracheal sounds can be useful in a variety of circumstances. First, the carries sound from within the , allowing auscultation of other sounds without filtering from the chest cage. Second, the characteristics of tra- cheal sounds are similar in quality to the abnormal bronchial heard

744 n engl j med 370;8 nejm.org february 20, 2014 The New England Journal of Medicine Downloaded from nejm.org at UNIV OF KENTUCKY on October 20, 2015. For personal use only. No other uses without permission. Copyright © 2014 Massachusetts Medical Society. All rights reserved. fundamentals of lung auscultation in with lung consolidation. Third, in tense . Recognizing this “tracheal wheeze” patients with upper-, tracheal is clinically important because when auscul- sounds can become frankly musical, character- tated over the lung, it is often mistakenly taken ized as either a typical or a localized, in- for the wheeze of (as discussed in more

Table 1. Clinical Characteristics and Correlations of Respiratory Sounds.

Respiratory Sound Clinical Characteristics Clinical Correlation Normal tracheal sound Hollow and nonmusical, clearly heard in both phases Transports intrapulmonary sounds, indicating upper- of respiratory cycle airway patency; can be disturbed (e.g., become more noisy or even musical) if upper-airway patency is altered; used to monitor sleep ; serves as a good model of bronchial breathing Normal lung sound Soft, nonmusical, heard only on inspiration and on Is diminished by factors affecting sound generation early expiration (e.g., , airway narrowing) or sound (e.g., lung destruction, , ); assessed as an aggregate score with normal breath sound; rules out clinically significant airway obstruction* Bronchial breathing Soft, nonmusical, heard on both phases of respiratory Indicates patent airway surrounded by consolidated cycle (mimics tracheal sound) lung tissue (e.g., ) or fibrosis Stridor Musical, high-pitched, may be heard over the upper Indicates upper-airway obstruction; associated with airways or at a distance without a extrathoracic lesions (e.g., , vocal- cord lesion, lesion after extubation) when heard on inspiration; associated with intrathoracic lesions (e.g., , , extrinsic compression) when heard on expiration; associated with fixed lesions (e.g., , paralysis of both , laryngeal mass or web) when biphasic Wheeze Musical, high-pitched; heard on inspiration, Suggests airway narrowing or blockage when localized expiration, or both (e.g., , tumor); associated with generalized airway narrowing and airflow limitation when widespread (e.g., in asthma, chronic ); degree of airflow limitation proportional to number of airways generating ; may be absent if airflow is too low (e.g., in severe asthma, destructive emphysema) Rhonchus Musical, low-pitched, similar to ; lower in Associated with rupture of fluid films and abnormal pitch than wheeze; may be heard on inspiration, airway collapsibility; often clears with coughing, expiration, or both suggesting a role for secretions in larger airways; is nonspecific; is common with airway narrowing caused by mucosal thickening or or by (e.g., and chronic obstructive pulmonary disease) Fine crackle Nonmusical, short, explosive; heard on mid-to-late Unrelated to secretions; associated with various inspiration and occasionally on expiration; (e.g., interstitial lung fibrosis, congestive failure, unaffected by , gravity-dependent, not pneumonia); can be earliest sign of disease (e.g., transmitted to mouth idiopathic , ); may be present before detection of changes on radiology Coarse crackle Nonmusical, short, explosive sounds; heard on early Indicates intermittent airway opening, may be related inspiration and throughout expiration; affected by to secretions (e.g., in chronic bronchitis) cough; transmitted to mouth Nonmusical, explosive, usually biphasic sounds; Associated with pleural or pleural typically heard over basal regions tumors Mixed sound with short musical component (short Associated with conditions affecting distal airways; wheeze) accompanied or preceded by crackles may suggest hypersensitivity pneumonia or other types of interstitial lung disease in patients who are not acutely ill; may indicate pneumonia in patients who are acutely ill

* Information is from Bohadana et al.3

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detail below). Finally, monitoring tracheal sounds Figure 1 (facing page). Acoustics and Waveforms is a noninvasive means of monitoring patients of Lung Sounds. for the , although for The left column shows typical values for the frequency practical reasons such monitoring cannot be (hertz) and duration (milliseconds) of the various performed by means of auscultation with a sounds. The middle and right columns show ampli- stethoscope.5 Whereas the stridorous breathing tude–time plots in unexpanded and time-expanded of a child with croup is easily recognized, stri- modes, respectively (amplitude is measured in arbi- trary units, and time in seconds). The unexpanded dor in adults, when caused by bronchial or plots contain screenshots of the entire sound, with a tracheal or by a tumor in the central vertical line showing where the time-expanded sections airway, is more subtle. It may be missed when (200 msec) were obtained. All tracings begin with inspira- only the lungs are examined but is obvious tion. The unexpanded waveform of the tracheal sound when heard over the trachea or .6 (Panel A) has strong inspiratory and expiratory compo- nents; the expanded waveform shows random fluctua- tions that are characteristic of white noise (a heteroge- Lung, or “Vesicular,” Sounds neous mixture of sound waves extending over a wide The sound of normal breathing heard over the range of frequencies). The vertical, regular spikes corre- surface of the chest is markedly influenced by the spond to . The unexpanded waveform of a anatomical structures between the site of sound normal (vesicular) breath (Panel B) has a strong inspira- generation and the site of auscultation. Char­ac­ tory component relative to the expiratory component; the expanded waveform is similar to that of a tracheal sound, teristically, normal lung sounds are heard clearly with random variation in amplitude. (A low-pass filter during inspiration but only in the early phase of allows easy passing of frequencies below a prescribed expiration (Fig. 1B). In sound analysis, the fre- frequency limit.) In bronchial breathing (Panel C), the quency range of normal lung sounds appears to be unexpanded waveform is characterized by similar am- narrower than that of tracheal sounds, extending plitudes of the inspiratory and expiratory components; the time-expanded waveform is like that seen with tracheal from below 100 Hz to 1000 Hz, with a sharp drop and normal breath sounds. The unexpanded waveform of 7 at approximately 100 to 200 Hz. The idea that stridor (Panel D) has a strong inspiratory component that “vesicular” sound is produced by air entering the appears as sinusoidal oscillations in the time-expanded alveoli (“vesicles”) is incorrect. Indeed, modern tracing. (The sinusoid is a waveform representing periodic concepts of physiology indicate that in the lung oscillations of constant amplitude, as indicated by a sine function. The fundamental frequency is the lowest fre- periphery gas molecules migrate by means of quency produced.) The unexpanded waveform of a diffusion from parts of the lung reached through wheeze (Panel E) has a strong expiratory component, bulk flow, a silent process. Most important, which appears as sinusoidal oscillations characteristic of studies support the idea of a double origin, with musical sounds in the time-expanded tracing. A rhonchus the inspiratory component generated within the (Panel F) can be distinguished from a wheeze by its lower lobar and segmental airways and the expiratory frequency, evident in the lower number of oscillations per unit of time in the time-expanded waveform. In the unex- 8,9 component coming from more central sources. panded waveform, fine crackles (Panel G) appear as Several mechanisms of vesicular sounds have spikes that correspond with the rapidly dampened wave been suggested, including turbulent f low, vortexes, deflections seen in the time-expanded tracing. Coarse and other, hitherto unknown mechanisms.10-12 crackles (Panel H) cannot be distinguished from fine Clinically, a decrease in sound intensity is the crackles in the unexpanded waveform; however, their longer duration is apparent in the time-expanded tracing. most common abnormality. Mechanistically, this The pleural friction rub (Panel I) has an unexpanded loss of intensity can be due to a decrease in the waveform characterized by a series of vertical spikes in a amount of sound energy at the site of generation, pattern that is undistinguishable from that produced by impaired transmission, or both.3 Sound genera- crackles. The lower frequency of the pleural friction rub is tion can be decreased when there is a drop in apparent in the time-expanded tracing. The short musical component of the squawk (Panel J) is seen in the unex- inspiratory airflow, which can result from sev- panded waveform as a large vertical spike in the middle of eral conditions, ranging from poor cooperation the inspiratory component of the normal breath sound. (e.g., a ’s unwillingness to take a deep However, the sinusoidal oscillations typical of musical breath) to of the central nervous sys- sounds are evident only in the time-expanded tracing. tem (e.g., drug overdose). Airway conditions in- Numerous accompanying crackles can be seen as small vertical spikes on both inspiration and expiration. See the clude blockage (e.g., by a foreign body or tumor) interactive graphic at NEJM.org. and the narrowing that occurs in obstructive

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Respiratory Sound Amplitude–Time Plot Acoustics Unexpanded time Expanded time

A Tracheal Sound 1.0 White noise 0.5 0.0 Typical frequency, 100–5000 Hz −0.5 Drop of energy at 800 Hz −1.0 0.0 1.0 2.0 3.0 4.0 5.0

B Normal (Vesicular) Lung Sound 1.0 Low-pass-filtered noise 0.5 0.0 Typical frequency, 100–1000 Hz −0.5 Drop of energy at 200 Hz −1.0 0.0 1.0 2.0 3.0 4.0 5.0

C Bronchial Breathing 1.0 Strong expiratory component 0.5 0.0 An intermediate sound between tracheal −0.5 and normal breathing −1.0 0.0 5.0 10.0

D Stridor 1.0 Sinusoid 0.5 0.0 Fundamental frequency, >500 Hz −0.5 −1.0 0.0 2.0 4.0 6.0 8.0

E Wheeze 1.0 Sinusoid 0.5 0.0 Typical frequency, >100–5000 Hz −0.5 Typical duration, >80 msec −1.0 0.0 1.0 2.0 3.0 4.0 5.0

F Rhonchus 1.0 Sinusoid 0.5 0.0 Typical frequency, about 150 Hz −0.5 Typical duration, >80 msec −1.0 0 5 10 15 20

G Fine Crackle 1.0 Rapidly dampened wave deflection 0.5 0.0 Typical frequency, about 650 Hz −0.5 Typical duration, about 5 msec −1.0 0 5 10 15

H Coarse Crackles 1.0 Rapidly dampened wave deflection 0.5 0.0 Typical frequency, about 350 Hz −0.5 Typical duration, about 15 msec −1.0 0.0 2.0 4.0 6.0 8.0

I Pleural Friction Rub 1.0 Rhythmic succession of short sounds 0.5 0.0 Typical frequency, <350hz −0.5 Typical duration, >15 msec −1.0 0.0 2.0 4.0 6.0

J Squawk 1.0 Sinusoid 0.5 0.0 Typical frequency, 200–300 Hz −0.5 Typical duration, about 200 msec −1.0 Followed or preceded by crackles 0.0 1.0 2.0 3.0 4.0 5.0

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airway diseases (e.g., asthma and chronic obstruc- than over the chest.14 Although stridor is usually tive pulmonary disease [COPD]). The decrease in inspiratory, it can also be expiratory or biphasic. the intensity of breath sounds may be permanent, Other causes of stridor in adults include as in cases of pure emphysema, or reversible, as in , airway edema after device removal, asthma (e.g., during a bronchial provocation test13 , vocal-cord dysfunction, or an asthma attack). of a foreign body, laryngeal tumors, thyroiditis, Sound transmission can be impaired by intra- and tracheal carcinoma. pulmonary or extrapulmonary factors. The latter The stridorous sound of vocal-cord dysfunction include conditions such as obesity, chest defor- deserves special mention because it is often con- mities (e.g., kyphoscoliosis), and abdominal dis- fused with asthma and is responsible for numer- tention due to ascites. Intrapulmonary factors, ous visits to the emergency department and hos- which can be harder to recognize, include dis- pitalizations. (Vocal-cord dysfunction, also called ruption of the mechanical properties of the lung paradoxical vocal-cord motion, is a respiratory parenchyma (e.g., a combination of hyperdisten- condition characterized by the inappropriate ad- tion and parenchymal destruction in emphysema) duction of the vocal cord with resultant airflow or the interposition of a medium between the limitation at the level of the larynx, accompanied source of sound generation and the stethoscope by stridorous breathing.) In a review of 95 patients that has a different acoustic impedance from with vocal-cord dysfunction who were treated at that of the normal parenchyma (e.g., collections the National Jewish Center, more than half carried of gas or liquid in the pleural space — pneumo- an incorrect diagnosis of asthma for years and , , and intrapulmonary masses). most had been treated with substantial doses of Incidentally, the development of lung consolida- glucocorticoids. These patients also had an aver- tion, which occurs in pneumonia, results in de- age of six hospitalizations yearly, and 28% had creased breath sounds only if the embedded been intubated.15 In addition, several reports have airways are blocked by inflammation or viscous documented the costs of misdiagnosed vocal- secretions. If instead the airways are patent, cord dysfunction to the medical care system.16 sound transmission is actually improved, increas- ing the expiratory component; this effect is char- Wheeze acterized as “bronchial breathing” (Fig. 1C), which The wheeze is probably the most easily recog- corresponds to the air bronchogram on chest nized adventitious sound.17 Its long duration, typi- radiographs. cally more than 100 msec, allows its musical qual- ity to be discerned by the ear. In sound Abnormal Respiratory Sounds analysis the wheeze appears as sinusoidal oscil- lations with sound energy in the range of 100 to Musical Sounds 1000 Hz and with harmonics that exceed 1000 Hz Stridor on occasion (Fig. 1E).18 It is probably incorrect to Stridor is a high-pitched, musical sound pro- credit high-pitched wheezes to the narrowing of duced as turbulent flow passes through a nar- peripheral airways and low-pitched wheezes to rowed segment of the upper .14 It the narrowing of central airways. Purportedly, is often intense, being clearly heard without the wheezes are formed in the branches between the aid of a stethoscope. In sound analysis it is char- second and seventh generations of the airway acterized by regular, sinusoidal oscillations with tree by the coupled oscillation of gas and airway a fundamental frequency of approximately 500 Hz, walls that have been narrowed to the point of often accompanied by several harmonics (Fig. 1D). apposition by a variety of mechanical forces.18 In Evaluating stridor is especially useful in patients addition, the model incorporates two principles: in the who have undergone first, that although wheezes are always associat- extubation, when its appearance can be a sign of ed with airflow limitation, airflow can be limit- extrathoracic airway obstruction requiring prompt ed in the absence of wheezes, and second, that intervention. In cases of such obstruction, stri- the pitch of an individual wheeze is determined dor can be distinguished from wheeze because it not by the diameter of the airway but by the is more clearly heard on inspiration than on ex- thickness of the airway wall, bending stiffness, piration and is more prominent over the neck and longitudinal tension.18

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Wheezes can be inspiratory, expiratory, or bi- crackles are altered by gravity, changing or disap- phasic. Although typically present in obstructive pearing with changes in body position (e.g., airway diseases, especially asthma, they are not bending forward). Coarse crackles tend to appear of any particular disease. In early during inspiration and throughout expira- asthma and COPD, wheezes can be heard all tion and have a “popping” quality. They may be over the chest, making their number difficult to heard over any lung region, are usually transmit- estimate. Localized wheeze is often related to a ted to the mouth, can change or disappear with local phenomenon, usually an obstruction by a coughing, and are not influenced by changes in foreign body, mucous plug, or tumor. Failure to body position. In sound analysis, crackles appear recognize this type of wheeze can have serious as rapidly dampened wave deflections with a re- consequences for patients, who often receive a petitive pattern (Fig. 1G and 1H). As compared misdiagnosis of “difficult-to-treat asthma”19 and with coarse crackles, fine crackles have a shorter are not referred to appropriate specialists for duration (5 msec vs. 15 msec) and higher fre- months or even years after the initial evaluation. quency (650 Hz vs. 350 Hz).20 The most likely Wheezes may be absent in patients with severe mechanism for the generation of fine crackles is airway obstruction. In fact, the model cited the sudden inspiratory opening of small airways above predicts that the more severe the obstruc- held closed by surface forces during the previous tion, the lower the likelihood of wheeze. The expiration.21 Coarse crackles are probably pro- typical example is a severe asthma attack, a con- duced by boluses of gas passing through airways as dition in which the low respiratory flows cannot they open and close intermittently.17 With the ex- provide the energy necessary to generate wheezes ception of the crackling sounds heard in moribund (or any sounds). As a consequence, the accom­ patients or in patients with abundant secretions, panying normal breath sound is also severely crackles are probably not produced by secretions. reduced or even absent, creating a clinical picture Evaluation for crackles is important because known as “silent lung.” As the obstruction is re- it can help with the . lieved and airflow increases, both the wheeze Because fine crackles have a distinctive sound and normal breath sounds reappear. that is similar to the sound heard when joined Finally, a word must be said about the rhon- strips of Velcro are gently separated, they have chus. This sound is considered to be a variant of been called Velcro rales. Typically, fine crackles the wheeze, differing from the wheeze in its are prominent in idiopathic pulmonary fibrosis, lower pitch — typically near 150 Hz — which is appearing first in the basal areas of the lungs responsible for its resemblance to the sound of and progressing to the upper zones with disease snoring on auscultation (Fig. 1F).17 The rhon- progression.22 However, fine crackles are not chus and the wheeze probably share the same pathognomonic of idiopathic pulmonary fibro- mechanism of generation, but the rhonchus, sis; they are also found in other interstitial dis- unlike the wheeze, may disappear after cough- eases, such as asbestosis, nonspecific interstitial ing, which suggests that secretions play a role. , and interstitial fibrosis associated Although many physicians still use the term with connective-tissue disorders. Notably, fine rhonchus, some prefer to refer to the character- crackles tend to be minimal or even absent in istic musical sounds simply as high-pitched or , probably because sarcoidosis primar- low-pitched wheezes. ily affects the central lung zones not abutting the pleura. Among patients with similar levels of Nonmusical Sounds scarring on chest films, those with few crackles Crackles are more likely to have sarcoidosis, whereas Crackles are short, explosive, nonmusical sounds those who have many crackles are more likely to heard on inspiration and sometimes during expi- have idiopathic pulmonary fibrosis. Advanced ration.17 Two categories of crackles have been computerized acoustic analysis, which involves described: fine crackles and coarse crackles. On the use of a multichannel sound-detection de- auscultation, fine crackles are usually heard dur- vice, has made it possible to diagnose idiopathic ing mid-to-late inspiration, are well perceived in pulmonary fibrosis and congestive , dependent lung regions, and are not transmitted in addition to other cardiopulmonary disorders, to the mouth. Uninfluenced by cough, fine with good sensitivity and specificity.23

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In idiopathic pulmonary fibrosis and asbestosis, pulmonary pressure, the basal regions undergo fine crackles can be discerned before radiologic greater expansion. Typically, the pleural friction abnormalities are detected and are thus consid- rub is biphasic, with the expiratory sequence of ered to be an early sign of pulmonary impair- sounds mirroring the inspiratory sequence.29 ment.24,25 Although the presence of Velcro rales Figure 1I shows individual components of a pleu- as heard on auscultation has not been formally ral friction rub. The waveform is similar to that accepted as diagnostic of idiopathic pulmonary seen with crackles, except for its longer duration fibrosis, auscultation is considered to be the only and lower frequency. The pleural friction rub is realistic means of detection early in the course of probably produced by the sudden release of tan- the disease.22 In asbestosis, the use of computer- gential energy from a lung surface that is tempo- ized detection of crackles has appeared to be as rarily prevented from sliding because of a fric- accurate as CT in locating disease that is not ra- tional force between the two pleural layers.29 diologically apparent.25 In a study of 386 workers Typically, pleural friction rubs are heard in in- exposed to asbestos,26 crackle detection by means flammatory diseases (e.g., pleuritis) or malig- of auscultation performed by a trained techni- nant pleural diseases (e.g., mesothelioma). cian correctly identified all the cases of asbesto- sis, suggesting that auscultation may have a role Mixed Sound — The Squawk to play as a noninvasive method of screening in Also called “short wheeze” or “squeak,” the squawk these populations. is a mixed sound, containing musical and non- Coarse crackles are commonly heard in pa- musical components. Figure 1J shows the sound tients with obstructive lung diseases, including analysis for a recorded squawk in a patient with COPD, , and asthma, usually in hypersensitivity pneumonitis. The short wheeze association with wheezes. They are also often appears as sinusoidal oscillations that are less heard in patients with pneumonia and those with than 200 msec in duration, with a fundamental congestive heart failure. In pneumonia, the char- frequency between 200 and 300 Hz. The mecha- acteristics of the crackles may vary markedly nism underlying the production of squawks is during the disease: the coarse, midinspiratory not entirely known, but according to one theory, crackles heard in the early phase give way to they are produced by the oscillation of peripheral shorter, end-inspiratory crackles in the recovery airways (in deflated lung zones) whose walls re- phase.27 Fine and coarse crackles may also co­ main in apposition long enough to oscillate un- exist.28 Finally, although crackles can be heard der the action of the inspiratory airflow.29 in healthy persons, the crackles tend to disap- Squawks are typically heard from the middle to pear after a few deep breaths. The presence of the end of inspiration in patients with interstitial persistent crackles in both lungs in older per- diseases, especially hypersensitivity pneumoni- sons with dyspnea should prompt an investiga- tis.30 However, they are not pathognomonic of tion for interstitial lung disease. this condition, having also been documented in diseases such as bronchiectasis and pneumo- Pleural Friction Rub nia.31 In a patient with squawk and no evidence In healthy persons, the parietal and visceral pleura of interstitial disease, pneumonia should be sus- slide over each other silently. In persons with pected, because it is the next most likely cause.31 various lung diseases, the visceral pleura can be- come rough enough that its passage over the pa- Conclusions rietal pleura produces crackling sounds heard as a friction rub. In our experience, this sound is Lung auscultation remains an essential part of more prominent on auscultation of the basal and the physical examination. No other clinical pro- axillary regions than on auscultation of the up- cedure matches auscultation for the provision of per regions. One explanation for this difference relevant clinical information about the respira- is the fact that the basal regions lie on the steep tory system quickly, easily, and by nearly univer- portion of the static pressure–volume curve, sally available means. Moreover, auscultation re- whereas the upper regions lie on the flat portion quires minimal cooperation on the part of the of the curve. Thus, for a given change in trans- patient, is cost-effective, and can be repeated as

750 n engl j med 370;8 nejm.org february 20, 2014 The New England Journal of Medicine Downloaded from nejm.org at UNIV OF KENTUCKY on October 20, 2015. For personal use only. No other uses without permission. Copyright © 2014 Massachusetts Medical Society. All rights reserved. fundamentals of lung auscultation often as necessary. The development of robust on its proper correlation with the available clini- acoustic devices for use at the bedside — as exem- cal information. plified by electronic paired with Dr. Izbicki reports receiving lecture fees from Novartis; small convenient recorders, perhaps in the form AstraZeneca; Teva; Pfizer; Merck, Sharp, and Dohme; and of a smartphone with an app — may provide the Neopharm, travel support from Novartis and GlaxoSmithKline, and grant support from Novartis, GlaxoSmithKline, and long-awaited portable objective means to record, AstraZeneca — all through his institution; and Dr. Kraman analyze, and store lung sounds just as any other reports providing expert testimony in workers’ compensation clinical information is measured and stored. This and medical malpractice cases. No other potential conflict of interest relevant to this article was reported. development will make sound tracking possible, Disclosure forms provided by the authors are available with further enhancing the usefulness of auscultation. the full text of this article at NEJM.org. Finally, it must be kept in mind that auscultation We thank Dr. Hans Pasterkamp for providing the stridor sound file, and Anto Yawanta and Jean-Pierre Michaely for is not a laboratory test but a component of the their technical assistance in the recording and analysis of lung physical examination whose usefulness depends sounds.

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