Quantitation of wheezing in acute asthma.

Pulmonary sounds were recorded before and after bronchodilator treatment in 20 patients with acute attacks of asthma. Analysis of the sounds showed that improvement in the forced expiratory volume in one second was associated with the following two changes in the sound signal: (1) the proportion of the respiratory cycle occupied by wheeze (Tw/Ttot ratio) was reduced from 86 percent to 31 percent on average; and (2) the sound frequency of the highest pitched wheeze was also reduced, from a mean of 440 Hz to 298 Hz.