Normal breath sounds are caused by the turbulent flow of air through the airways (not the alveoli). They are transmitted to the chest wall through the lungs (see Table 3.4).
Added breath sounds
These are divided into wheezes from the airways, crackles, which come from the large airways, the bronchioles and the alveoli, and friction rubs from the pleura (see Table 3.5)
Wheezes are musical sounds caused by airway obstruction and are usually heard in expiration.
· A low-pitched monophonic wheeze is caused by obstruction of a single large airway (below the trachea). It is caused by bronchial carcinoma or inhaled foreign body, and is frequently inspiratory.
· A high-pitched expiratory wheeze, often with a mixture of notes ‘polyphonic wheeze’ is caused by obstruction of many smaller airways as occurs in asthma and chronic obstructive pulmonary disease (COPD). However, these conditions may occur without wheeze, despite severe obstruction.
Crackles/crepitations: Normally the airways do not collapse or obstruct on expiration, but they may due to secretions and oedema or damage by either fibrosis or loss of elasticity. The reopening of collapsed small airways and alveoli or the presence of secretions in the larger air-ways cause inspiratory crackles. They are differentiated by their timing and nature:
· Early inspiratory crackles come from the airways, where air reaches them first in inspiration. Late or paninspiratory crackles come from the alveoli.
· ‘Fine crackles’ are usually alveolar (late) and are often described as rubbing hair through fingers. They are typical of pulmonary fibrosis or alveolar oedema.
· Coarse crackles are wet, low-pitched early inspiratory sounds due to airway secretions, often changed in nature by coughing.
Pleural friction rub: A creaking sound in inspiration and expiration, localised over an area of pleural inflammation. Causes include viral or bacterial pneumonia and pulmonary infarct/embolus.