Lung Auscultation Biography
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Lung sounds, also referred to as
respiratory sounds or breath sounds, can be auscultated across the anterior and
posterior chest walls with a stethoscope. Adventitious lung sounds are
referenced as crackles (rales), wheezes (rhonchi), stridor and pleural rubs as
well as voiced sounds that include egophony, bronchophony and whispered
pectoriloquy. Descriptions and audio recordings for all of these sounds are
available on this website. While we have breath sound courses and reference
guides, some users prefer to use these quick links to concise information and
audio recordings for both normal and adventitious sounds. Chest auscultation
has long been considered a useful part of the physical examination, going back
to the time of Hippocrates. However, it did not become a widespread practice
until the invention of the stethoscope by René Laënnec in 1816, which made the
practice convenient and hygienic.1During the second half of the 20th century,
technological advances in ultrasonography, radiographic computed tomography
(CT), and magnetic resonance imaging shifted interest from lung auscultation to
imaging studies, which can detect lung disease with an accuracy never
previously imagined. However, modern computer-assisted techniques have also
allowed precise recording and analysis of lung sounds, 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. 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 crackles) are produced. “Crackle” can be defined acoustically
and does not suggest any means or site of generation. The clinical
characteristics of normal and fadventitious sounds are summarized in Table
1TABLE can be heard in aninteractive graphic, available with the full text of
this article at NEJM.org. 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 neck,
normal tracheal sounds characteristically contain a large amount of sound
energy and are easily heard during the two phases of the respiratory cycle
(Figure 1AFIGURE and Waveforms of Lung Sounds.).
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 pharynx, glottis, and subglottic region. Listening to tracheal sounds can be useful in a variety of circumstances. First, the trachea carries sound from within the lungs, allowing auscultation of other sounds without filtering from the chest cage. Second, the characteristics of tracheal sounds are similar in quality to the abnormal bronchial breathing heard in patients with lung consolidation. Third, in patients with upper-airway obstruction, tracheal sounds can become frankly musical, characterized as either a typical stridor or a localized, intense wheeze. Recognizing this “tracheal wheeze” is clinically important because when auscultated over the lung, it is often mistakenly taken for the wheeze of asthma (as discussed in more detail below). Finally, monitoring tracheal sounds is a noninvasive means of monitoring patients for the sleep apnea syndrome, although for practical reasons such monitoring cannot be performed by means of auscultation with a stethoscope.5 Whereas the stridorous breathing of a child with croup is easily recognized, stridor in adults, when caused by bronchial or tracheal stenosis or by a tumor in the central airway, is more subtle. It may be missed when only the lungs are examined but is obvious when heard over the trachea or larynx.
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 pharynx, glottis, and subglottic region. Listening to tracheal sounds can be useful in a variety of circumstances. First, the trachea carries sound from within the lungs, allowing auscultation of other sounds without filtering from the chest cage. Second, the characteristics of tracheal sounds are similar in quality to the abnormal bronchial breathing heard in patients with lung consolidation. Third, in patients with upper-airway obstruction, tracheal sounds can become frankly musical, characterized as either a typical stridor or a localized, intense wheeze. Recognizing this “tracheal wheeze” is clinically important because when auscultated over the lung, it is often mistakenly taken for the wheeze of asthma (as discussed in more detail below). Finally, monitoring tracheal sounds is a noninvasive means of monitoring patients for the sleep apnea syndrome, although for practical reasons such monitoring cannot be performed by means of auscultation with a stethoscope.5 Whereas the stridorous breathing of a child with croup is easily recognized, stridor in adults, when caused by bronchial or tracheal stenosis or by a tumor in the central airway, is more subtle. It may be missed when only the lungs are examined but is obvious when heard over the trachea or larynx.
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