Table 3 summarises the changes in breath and voice sounds heard in five common lung conditions. Crackles are brief, explosive sounds thought to arise either from bubbling of air through airway secretions or explosive reopening of airways. Coarse inspiratory and expiratory crackles that may clear on coughing are a feature of bronchiectasis. Fine mid to late inspiratory crackles are a feature of interstitial fibrosis and pulmonary oedema. Early inspiratory crackles may sometimes be heard in chronic bronchitis and emphysema.
Wheezes arise from the oscillations of narrowed airways and their adjacent tissues.
Widespread polyphonic expiratory wheezes are a feature of asthma and airway obstruction in chronic bronchitis and emphysema. A fixed monophonic wheeze may result from localised narrowing of an airway most commonly due to a carcinoma. A fixed inspiratory wheeze is termed stridor and is caused by obstruction of the upper airways. Occasionally sequential inspiratory wheezes or squawks may be heard in patients with pulmonary fibrosis. Pleural rubs are caused by friction between two inflamed pleural surfaces and vary in quality from a creak to a musical note.