Clinical meaning
Lung sounds are generated by turbulent airflow through the tracheobronchial tree and are transmitted through the lung parenchyma and chest wall to the stethoscope. Normal breath sounds are classified by location: vesicular sounds (soft, low-pitched, heard over peripheral lung fields, with inspiration longer than expiration in a 3:1 ratio), bronchovesicular sounds (moderate pitch, heard over the mainstem bronchi at the 1st-2nd intercostal spaces and between the scapulae, with equal inspiratory and expiratory phases), and bronchial/tracheal sounds (loud, high-pitched, heard over the trachea, with expiration longer than inspiration). When bronchial breath sounds are heard in peripheral lung fields, this indicates consolidation (pneumonia, atelectasis) where fluid-filled or collapsed alveoli transmit the central airway sounds more efficiently than air-filled alveoli. Adventitious (abnormal) sounds arise from specific pathological mechanisms. Crackles (formerly called rales) result from the sudden opening of collapsed small airways and alveoli during inspiration. Fine crackles (high-pitched, brief, at end-inspiration) are produced by the popping open of fluid-filled or atelectatic alveoli and are characteristic of pulmonary fibrosis, early heart failure, and pneumonia. Coarse crackles (low-pitched, longer duration, early-to-mid inspiration) result from air bubbling through secretions in larger airways and are heard in bronchitis, pulmonary edema, and bronchiectasis. Wheezes result from airflow through narrowed airways -- the turbulent airflow sets the airway walls vibrating at an audible frequency. High-pitched wheezes (musical, continuous) indicate bronchospasm (asthma, COPD exacerbation) or mucosal edema. Low-pitched wheezes (rhonchi) suggest secretions in larger airways and often clear with coughing. Stridor is an ominous inspiratory wheeze heard over the trachea indicating upper airway obstruction (laryngeal edema, foreign body, epiglottitis). Pleural friction rubs are creaking, grating sounds produced by inflamed parietal and visceral pleural surfaces rubbing together during respiration, heard in pleurisy, pulmonary embolism, and pleural infection.