Modification of respiratory sinus arrhythmia by mean heart rate

Four different spectral methods for assessing the respiratory sinus arrhythmia (=RSA) are investigated: the spectrum of the tachogram, of the point process and of two subcases of the step-like interpolation algorithm. For a comparison the integral pulse frequency modulation model is applied. In the case that the mean heart interval is about 1 and breathing frequency is smaller than 0.1 Hz, all four methods are approximately equivalent. In the case that the breathing frequency is comparable with the mean heart rate, large discrepancies may occur giving rise to systematical errors if the spectra are not corrected This is especially important when the RSA is assessed as a function of breathing frequency