Analysis of spectral and wavelet-based measures used to assess cardiac pathology

In previous studies of heart rate variability in humans, it has been demonstrated that the scale-dependent wavelet transform (WT) standard deviation [σ_wav(m)] of the interbeat intervals can be used to discriminate patients with certain forms of cardiac dysfunction from normal subjects. This paper forges an explicit link between this measure and a corresponding spectral measure, which is also shown to provide discrimination between the two classes of data. The statistics of the estimator for σ_wav(m) are obtained in the analytically simplest case, including expressions for its bias and variance. Numerical simulations are provided to support the theoretical analysis. We compare the bias, variance, and frequency resolution of the WT and spectral measures, and conclude that the former appears more suited to our particular circumstances