Application of the cone-kernel distribution to study the effect of myocardial contractility in the genesis of the first heart sound in dog

In order to examine the effect of myocardial contractility in the production of the first heart sound (S1), the cone-kernel distribution (CKD) was applied to the thoracic S1 in dogs under various cardiac contractile states. The results showed that the dominant components of S1 are highly concentrated in a specific frequency band between 30 and 50 Hz with a horizontal flat or a semi-lunar shape, independent of the myocardial contractile state. There was no systematic increasing frequency component in the signal distributions like that found in the muscle sound. These results suggest that the myocardial contribution in S1 may be absent. However, there is some evidence that the myocardial contribution may be obscured by the other stronger components, and thus cannot be detected by the time-frequency representation (TFR) techniques