Estimation of frequency shift in cardiovascular variability signals

Spectral analysis of heart rate (HR) and blood pressure (BP) oscillations has traditionally been concen-trated on the spectral power. However, a shift in spectral frequency characterizes the variability better than the power in some cases. We compared three parameters to estimate spectral shift within the low frequency (LF, 0.04-0.15Hz) band in HR and BP variability: mean (fmean), median (fmed), and central fre-quency (fc). Parameter variance (pstd) and sensitivity to noise were estimated with realistic HR, systolic BP (SBP) and diastolic BP (DBP) data. The fmean showed the lowest parameter variance both for AR (e.g. for SBP pstd 3.1 vs. 4.8 vs. 4.7mHz for fmean, fmed and fc, respectively; p<0.001) and FFT based (e.g. for SBP pstd 4.7 vs 7.7mHz for fmean and fmed, respectively; p<0.001) methods. Furthermore, fmean was least sensitive to noise. The fc showed the poorest performance being especially sensitive to noise. We computed fmean for experimental data from 14 healthy males in control and pharmacological blockade conditions. When parasympathetic control was reduced, LF oscillations of HR and BP tend to shift to-wards lower frequencies. These shifts are often masked if the fmean is not computed separately for differ-ent spectral bands. Thus, band-wise analysis of spectral shift in cardiovascular variability signals pro-vides important information. To analyze the spectral shift, the fmean is the preferred parameter, which outweighs especially the fc; the parameter used in the most previous studies, which have quantified the frequency of oscillations in cardiovascular signals.