Spectral analysis of heart rate variability as a measure of sympathico-vagal influence after sublingual nitroglycerin: comparison of the quantitative analysis with FFT and autoregressive model

Short-acting vasodilating drugs like nitroglycerin sublingual (NTG) change sympathico-vagal balance as long as central systolic blood pressure is lowered. To calculate power spectral density (PSD) estimation of heart rate variability (HRV) stationary conditions in the time domain are required. In order to study time course of HRV after administration of NTG, two different methods were used. One method is the chirp-z transformation which is closely related to the Fourier transformation; the other method is an autoregressive (AR) model. AR models offer the possibility of analyzing short time fractions for a complete spectra, whereas the chirp-z transformations need a definite number of points for a definite frequency region. No significant differences could be seen in PSD calculated with the different methods