Adventitious or abnormal sounds
- friction rubs
- distinguish these from friction sounds of the stethoscope on the chest wall and by muscular activity within the chest wall
Breath sounds are decreased or absent when air flow is decreased eg. Bronchial obstruction, muscular weakness or pulmonary empyema, in which there is an abnormally large amount of air that damps the sound.
Additionally, breath sounds may be decreased when fluid or tissue separates the air passages from the stethoscope (obesity or pleural disease). As vibrations may be partially reflected at air-fluid or dense tissue interfaces.
The commonest cause of abnormal bronchial breathing is consolidation of the lung. When consolidation occurs, damping action of air-containing alveoli of diminished, allowing underlying higher frequency bronchial sounds to be heard without alteration.
If breath sounds are diminished or if you suspect but cannot hear signs of abstructive breathing, ask the patient to breathe hard and fast with his mouth open. The diminished breath sounds associated with obesity may become readily audible, wheezes and ronchi that were previously inaudible may appear.
Breath sounds remain decreased in emphysema. Wheezes or rhonchi may appear in emphysema, asthma or bronchitis.
Bates, Barbara. 1974. A Guide to Physical Examination. J.B. Lippincott Company, Toronto.