Character of the breath sounds
Three different types of breath sounds can be identified: vesicular, bronchial and puerile breath sounds.
Vesicular or normal breath sounds are heard in healthy people (except in infants and toddlers) across all lung fields. It is a low frequency, clear sound, whereby the inspiration is quietly audible and the expiration even quieter still, with an audible ratio between inspiration and expiration of 3:1.
Under physiological circumstances, bronchial breath sounds are only heard above the trachea and mainstem bronchi. It is a very loud, high-frequency, sharp sound, in which the inspiration is more clearly audible than the expiration and the ratio between audible inspiration and expiration is equivalent to the actual ratio (5:6). Bronchial breath sounds identified in areas of the thorax other those mentioned above are always pathological. They develop due to a lack of aerated tissue, which means that higher frequencies are transmitted better. The best-known example is the lung infiltrate (pneumonia) where the alveoli are closed by an influx of inflammatory cells and/or are filled with exudate with the bronchi left open.
Puerile breath sounds are audible across all lung fields in newborns and toddlers. They differ from vesicular breath sounds in loudness and character. Puerile breath sounds are somewhat louder and sharper as a result of the shorter distance between the stetho-scope and the aerated tissue because of the thinner thoracic wall.
Intensity
The intensity of the breath sounds can be normal or reduced. When the loudness is reduced this is called decreased breath sounds.
This can be a result of:
Generalised pathology:
- increased aeration of the surrounding lung tissue (e.g. COPD; hyperinflation of the lungs)
- increased distance from the stethoscope to the airways (for example obesity)
- reduced respiratory excursions (e.g. neuromuscular disorders, final stages of asthma attack).
Localised pathology:
- reduced aeration of the lung tissue (e.g. atelectasis)
- increased distance from the stethoscope to the airways (for example pneumothorax).
Ratio of inspiration and expiration time
The actual ratio between inspiration and expiration is 5:6. During auscultation, however, a ratio of 3:1 is heard under physiological circumstances.
If during auscultation the expiration is as long, or longer than the inspiration then this is called prolonged expiration. This points to an obstruction of the lower airways, as seen with asthma, for example. It is often accompanied by a wheezing noise. In extreme cases this is called an expiratory stridor.
Prolonged inspiration points to an obstruction of the upper airways [e.g. in the larynx or trachea as a result of pseudocroup (subglottic laryngitis) or a foreign body]. Often this can already be heard from a distance and frequently it is accompanied by a harsh, high-pitched sound; in these cases it is called inspiratory stridor.