Estimation of frequency shift in cardiovascular variability signals
Spectral analysis of heart rate (HR) and blood pressure (BP) oscillations has traditionally concentrated on spectral power, although a shift in spectral frequency characterises the variability better than power in some cases. Experimental data were obtained from 14 healthy males in control and pharmacological blockade conditions. When parasympathetic control was reduced, LF oscillations of HR and BP tend to shift towards lower frequencies. Three parameters were compared to estimate the spectral shift within the low frequency (LF, 0.04-0.15 Hz) band in HR and BP variability. mean (f(mean)), median (f(med)), and central frequency (f(c)). Parameter variance (P-STD) and sensitivity to noise were also estimated using realistic HR, systolic BP (SBP) and diastolic BP (DBP) data. f(mean) showed the lowest parameter variance 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 (SBP P-STD 4.7 vs 7.7 mHz for f(mean) and f(med), respectively, p <0.001). Furthermore, f(mean) was least sensitive to noise. f(c) showed the poorest performance 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 across different spectral bands.
variability spectral analysis heart rate blood pressure central frequency mean frequency