Acoustical studies on respiratory sounds in asthmatic patients

Changes in the breathing sounds such as stridor and dry and wet rales in asthmatic patients were studied. The breathing sounds were recorded with the small transistor warp type microphone inserted through the nasal orifice into the trachea, main bronchi and segmental bronchi, and were analyzed with sound analyzer. The results were as follows: The whistling rales were caused by the resonance of the bronchial wall, when the vibrating frequency was coincident with its specific frequency. Snoring rales were explained as the sound caused by the air flow passing promptly through contracted bronchi with little secretion. Resonance of either bronchial wall or highly viscous sputum was considered to be responsible for the sonorous rales. Sibilant rales were audible when bronchi promptly repeated dilation and contraction. Stridor was picked up at the upper part of the air tract, from the main bronchus to the trachea, and noise was the main component on the sonogram, presumably caused by the air turbulence due to the narrowing and deformity of bronchial tube or to the sputum adhering to the inner surface of the air tract.