Table 1 The understanding of normal and abnormal lung sounds

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