Time Frequency Transforms Of The Human First Heart Sound
The frequency dynamics of the human first heart sound were assessed at 27 locations across the human thorax using Reduced Interference time-frequency transforms. Time-frequency transformation demonstrated prominent impulse-like components in the superior thorax. In this region, signal dynamics were well described by the instantaneous power and the power spectrum. Spectra from the inferior thorax, however, revealed signal components whose frequency rose rapidly during the isovolumic contraction period. Statistics based upon the joint time-frequency spectrum, such as the instantaneous modal frequency, were necessary to capture heart sound frequency variation. These studies demonstrate that the externally recorded human first heart sound is a non-stationary signal and suggest that time-frequency transforms may be useful in relating human first heart sound frequency dynamics to the underlying vibrational mechanics.