Time-frequency analysis of 24-hour heart rate fluctuation for the characterization of very low-frequency component

A smooth pseudo Wigner-Ville distribution was employed to investigate both time and frequency characteristics in a very low-frequency component (less than 0.04 Hz) of 24-hour heart rate fluctuation. In some cases of heart failure the authors could see remarkable and very low-frequency oscillations of the Wigner-Ville distribution, which are related to Cheyne-Stokes respiration. However the Wigner-Ville distribution of normal subjects did not have such oscillations, but more random spectral characteristics instead. Furthermore, the authors calculated 1/f^α regression slopes of average spectrum to be a crude estimate of fractal dimensions. The slopes are more negative in heart failure patients than normals (-1.866±0.888 vs. -0.957±0.180 p<0.005), which associates a loss of dimensionality of heart rate fluctuation in heart failure