Quantification of first heart sound frequency dynamics across the human chest wall.

Power spectral analysis has attracted attention because of its potential for non-invasive cardiac diagnosis. However, time-frequency analysis of first heart sound frequency dynamics from canine epicardium has demonstrated that cardiac vibrations are fundamentally multi-component and non-stationary, questioning the validity of power spectral techniques. In this study, we employed time-frequency transforms to characterise first heart sound frequency dynamics from 27 sites across the human thorax. In contrast to the dynamics observed epicardially, the first heart sound frequency law was dominated by quasi-stationary and impulse-like components implying that the instantaneous power and the power spectrum contain most of the diagnostic information in the first heart sound.