TIME-FREQUENCY ANALYSIS OF THE MUSCLE SOUND OF THE HUMAN DIAPHRAGM

The time-frequency characteristics of muscular sounds (phonomyogram) p roduced by the contraction of the human diaphragm under various contra ctile states is evaluated with the cone-kernel distribution. The resul ts show that the instantaneous frequency of the phonomyogram of the di aphragm has a high cross-correlation (an average of 0.91+/-0.06) with the transdiaphragmatic pressure, with a delay varying between 25 and 3 5ms. The instantaneous frequency response of the phonomyogram of the d iaphragm shows a behaviour similar to that of the frog muscle; it rapi dly rises and then fades out. However, the maximum of the instantaneou s frequency of the phonomyogram of the diaphragm is not proportional t o the maximum of the transdiaphragmatic pressure. This analysis also d emonstrates the usefulness of the cone-kernel distribution for studyin g frequency-modulated signals like the muscular sound signals.