Table 1.

The understanding of normal and abnormal lung sounds

Categories of lung sounds	Produce/Cause	Timing	Acoustics characteristics	Associated disease
Normal
Tracheal	Turbulent airflow through pharynx and glottis	Both inspiration and expiration	Hollow, non-musical, harsh; High-pitch, 100–5000 Hz, drop at 800 Hz	–
Bronchial	Airflow traversing from trachea to the main airways	Inspiration, mostly expiration	Soft, non-musical, tubular; High-pitch, similar to tracheal	–
Vesicular	Airflow through smaller airways and alveoli	Inspiration, early expiration	Soft, non-musical; Low-pitch, 100–1000 Hz, drop at 200 Hz	–
Bronchovesicular	Airflow through bronchi and alveoli	Both inspiration and expiration	Frequency between vesicular and bronchial	–
Abnormal
Fine crackle	Explosive opening of small airways or the alveoli	Mid-to-late inspiration, occasionally expiration	Explosive, non-musical; High-pitch, 650 Hz; Duration: 5 ms	Interstitial lung fibrosis, pneumonia, pulmonary fibrosis, asbestosis
Coarse crackle	Air bubble in larger airways	Expiratory, mostly early inspiratory	Explosive, non-musical; Low-pitch, 350 Hz; Duration: 15 ms	COPD, bronchiectasis, asthma
Pleural rub	Pleural membrane rubbing against each other	Biphasic	Non-musical, rhythmic; Low-pitch, 350 Hz; Duration: 15 ms	Pleural inflammation, pleural tumors
Wheeze	Airflow limitation, airway narrowing	Inspiratory, mostly expiration	Musical, sibilant; High-pitch, > 100 Hz; Duration: > 80 ms	COPD, asthma, foreign body
Rhonchi	Thickening of secretions in bronchial tree	Inspiratory, mostly expiratory	Musical, sibilant; Low-pitch, 200 Hz; Duration: > 80 ms	Bronchitis, COPD
Stridor	Upper airway obstruction	Mostly inspiratory, sometimes both	Musical, sibilant; High-pitch, 500 Hz; Duration: > 250 ms	Epiglottitis, foreign body, croup, laryngeal oedema

“-” none, COPD chronic obstructive pulmonary disease