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Spectral analysis of respiratory sounds to assess bronchodilator effect in asthmatic patients

Analysis of respiratory sounds is a promising technique that could improve results obtained by classical spirometry. Spectral characteristics of respiratory sounds, during forced expiration manoeuvres, have been studied for asthma patients and normal subjects in order to assess the response to a bronchodilator, Sound signals have been analysed for different airflow levels. An autoregressive model (order 16) has been used and 3 spectral parameters were calculated: central frequency (Fc), central frequency in the range 300-2500 Hz (Fc*) and power ratio at 300 Hz (R300). The initial variability of this protocol was reduced by means of a threshold criterion, based on R300 ratio, which rejected episodes where contribution of wheezing was not relevant. Frequency components related only to wheezing did not change during this protocol. Analysis of main frequency of wheezing, by means of parameter Fc*, seems not to be appropriated to assess the bronchodilatador effect. Analysis of low and high frequency distribution of respiratory sound spectrum was performed using the Fc parameter. The drug effect was assessed in the asthmatic group and significant decreasing of Fc was observed. No significant variations were found for the control group.