Estimation of frequency shift in cardiovascular variability signals

Spectral analysis of heart rate (HR) and blood pressure (BP) oscillations h as traditionally concentrated on spectral power, although a shift in spectr al frequency characterises the variability better than power in some cases. Experimental data were obtained from 14 healthy males in control and pharm acological blockade conditions. When parasympathetic control was reduced, L F oscillations of HR and BP tend to shift towards lower frequencies. Three parameters were compared to estimate the spectral shift within the low freq uency (LF, 0.04-0.15 Hz) band in HR and BP variability. mean (f(mean)), med ian (f(med)), and central frequency (f(c)). Parameter variance (P-STD) and sensitivity to noise were also estimated using realistic HR, systolic BP (S BP) and diastolic BP (DBP) data. f(mean) showed the lowest parameter varian ce both for an autoregressive (AR) method (SBP P-STD 3.1 vs 4.8 vs 4.7 mHz for f(mean), f(med) and f(c), respectively, p <0.001) and an FFT method (SB P P-STD 4.7 vs 7.7 mHz for f(mean) and f(med), respectively, p <0.001). Fur thermore, f(mean) was least sensitive to noise. f(c) showed the poorest per formance being especially sensitive to noise. To analyse the spectral shift , f(mean) is preferred, since it performs better than f(c), which has been used in most previous studies. To quantify the frequency of oscillations in cardiovascular signals, the mean frequency is recommended, with analyses a cross different spectral bands.