1/f Modeling of Blood Pressure and Heart Rate Spectra

The first observations of a 1/f trend in the spectrum of heart rate (HR) and blood pressure (BP) signals date back to 1982 and 1990, respectively. Ever since, a number of studies have suggested that the analysis of this spectral trend may be a valuable tool for investigating the physiological mechanisms involved in cardiovascular regulation and for assessing their derangement in pathological conditions. The spectral analysis of BP and HR tracings recorded in cats before and after the surgical opening of the baroreflex loop, offered us the opportunity to address some yet unclear aspects related to the 1/f trend occurring in BP and HR spectra, namely: 1) the role played by the baroreflex in the genesis of the 1/f trend; 2) the ability of a single 1/f curve to correctly model the spectra; 3) the methodology required for the estimation of the regression line corresponding to the 1/f curve when spectra are plotted in a log-Iog scale. The results we obtained indicate that 1) baroreflex denervation disrupts the 1/f trend of BP spectra but does not modify the same trend in the HR spectra; 2) in pathological conditions a single 1/f line may be inadequate to describe the BP spectra; and 3) the slope of the regression line representing the 1/f trend strongly dependent on the frequency region over which the line is estimated, thus prompting for the establishment of standards in the modeling procedure.