Comparison of techniques for estimating baroreflex gain from heart rate and blood pressure spectra

Heart rate and blood pressure are linked by the baroreflex mechanism. Baroreflex gain can be estimated from the ratio of RR interval to systolic pressure spectra. This value, α, has units of ms mmHg-1. The aim of this study was to quantify the effect of using four different techniques for estimating the spectra on estimates of α. Nine healthy subjects were studied. Each relaxed supine for 20 min, ECG (lead II) and finger blood pressure (Finapres) signals were then recorded to computer with a sample rate of 250 Hz. Each recording was 5 min long. RR interval and systolic pressure sequences were resampled at 4 Hz and transformed into the frequency domain using an averaged Fast Fourier Transform (FFT), averaged zero padded FFT (FFTZ), widowed autocovariance function (ACVF) and the maximum entropy method (ME). This study shows that the use of different spectral analysis techniques does not significantly affect estimation of baroreflex gain, α, and that the results of different studies can be compared.