Respiratory Sounds

Definition and PathogenesisTop

1. Normal respiratory sounds:

1) Normal lung or “vesicular” sounds are soft, nonmusical, and audible over almost entire peripheral lung zones during inspiration and early expiration. They are produced by turbulent air flow through lobar and segmental bronchi. In disease states, there may be diminished intensity due to decreased generation of sound energy, impaired sound transmission, or both. Decrease in sound generation may be due to impaired respiratory drive or impaired flow of air to the peripheral airways (foreign body or obstructive airway diseases). Impaired transmission of sounds may be due to the presence of fluid or air in the pleural space, consolidated lung, large bullae in patients with emphysema, or by chest wall deformities or obesity.

2) Normal tracheal sounds are hollow nonmusical sounds with a wide spectrum of frequencies that are clearly heard at the suprasternal notch or the lateral neck in both respiratory cycles. Pathologic tracheal or “bronchial” sounds are audible over peripheral lung areas and may suggest lung consolidation (due to inflammation, infection, hemorrhage, protein, or malignancy). In patients with upper airway obstruction, tracheal sounds may become musical and can present as either stridor or localized wheeze.

2. Abnormal respiratory sounds:

1) Crackles are nonmusical, short (<0.25 seconds), explosive respiratory sounds heard mostly during inspiration, caused by the sudden equalization of gas pressures between two areas of the lung. They occur during the opening of previously closed small airways. Crackles may be transiently apparent in healthy people but disappear after a few deep inspirations.

a) Fine crackles, previously termed crepitations or “velcro rales,” are heard mid-to-late inspiration mostly in dependent lung regions, uninfluenced by cough or body position, and not transmitted to the mouth. These high-pitched sounds may be due to pulmonary fibrosis, congestive heart failure, or pneumonia. Of note, fine crackles are minimal or absent in sarcoidosis, as the disease affects mostly central lung zones.

b) Coarse crackles are heard early in inspiration and throughout expiration, can be transmitted to the mouth, and can change with cough, but they are not influenced by changes in body position. These low-pitched sounds are commonly observed in the setting of bronchiectasis and other conditions characterized by secretions in the airways.

2) Wheezes and rhonchi are musical continuous breath sounds (>0.25 seconds), which may be high-pitched (wheezes) or low-pitched (rhonchi) and are generally audible during expiration. Wheezes (hissing, whistling sounds) are produced by the turbulent flow of air through narrowed airways, while rhonchi are mainly caused by secretions present in the airways. Expiratory wheeze is mostly caused by narrowing of the airways within the chest, which can occur in the setting of asthma, chronic obstructive pulmonary disease, aspiration of gastric contents, or heart failure. Of note, localized wheeze may be due to a focal process, including a tumor, foreign body, or mucous plug.

3) Stridor is a particularly loud, high-pitched, continuous sound, more clearly heard on inspiration over the upper airways or sometimes even without a stethoscope. This sound is caused by large airway narrowing and may indicate obstruction of the larynx or trachea. Stridor may be heard in patients with vocal cord dysfunction, epiglottitis, airway edema, anaphylaxis, laryngotracheitis, extrinsic compression of the trachea, or a foreign body.

4) Squawk, also known as “squeak,” is a mixed sound consisting of short wheezes accompanied by crackles that are heard in the middle to the end of inspiration. Squawks are most frequently present in patients with hypersensitivity pneumonitis and less often in patients with other interstitial lung diseases, bronchiectasis, or pneumonia.

5) Pleural friction rub is caused by the rubbing of the parietal and visceral layers of the pleura due to the deposition of fibrin in the course of an inflammatory or neoplastic process. This is generally biphasic in nature and heard best in basal and axillary regions.

DiagnosisTop

History and physical examination (differential diagnosis of respiratory diseases: Table 1). Diagnostic studies include mainly chest radiography, which may be supplemented with computed tomography (CT) of the thorax and pulmonary function tests (spirometry and others). In patients with dyspnea it is useful to perform pulse oximetry and, if abnormal, arterial blood gas measurements.

TablesTop