Four signal processing techniques for continuous baroreflex determination

Heart rate baroreflex sensitivity (BRS) is given as a ratio of inter-beat intervals (IBI) and systolic blood pressure (SBP) variations. This paper compares the feasibility of four techniques for continuous BRS determination: sequence technique, modified complex demodulation and alpha index technique and LP model technique. Blood pressure of healthy subjects (age 21-22 years) was recorded at rest (3 min), during exercise (0.5 W/kg of body weight, 9 min) and at rest (6 min) after exercise. The controlled breathing (20 breaths per min) was used at rest. To test the methods thirty-eight records were analyzed. The sequence technique determines the BRS from spontaneous variations of IBI and SBP in time. The complex demodulation technique determines the BRS as a ratio of the IBI and SBP signal amplitudes filtered by a band-pass filter with a 0.1 Hz frequency center. The alpha techniques and the LP techniques are spectral techniques, In the last two techniques a window of a few tenths of seconds duration simultaneously slides from the beginning to the end of both IBI and SBP signals. For each window the spectra of both signals are computed. The standard Fourier transform is used to determine the spectra for the alpha index technique. The ratio of amplitudes of the dominant spectral components in IBI and SBP spectre having near frequencies gives the BRS at the central window time and the corresponding frequencies. The linear prediction (LP) technique determines the spectrum as the inverse of the whitening filter transfer function. The residue at poles of the IBI and SBP LP spectral functions are determined. The ratio of IBI and SBP transfer functions corresponding to residua of frequency near paired poles gives the BRS at these frequencies. Determined values are attached to the center time of the window. All used techniques of BRS determination yield similar results. Averaged curves of the BRS changes are identical with those of IBI, but they differ from those of SBP and diastolic blood pressure