Relationships among spectral measures of baroreflex sensitivity and indices of cardiac vagal control.

Traditionally baroreflex sensitivity (BRS) has been assessed with pharmacological approaches such as phenylephrine infusion. Recently, non-invasive approaches using spectral analytic techniques have been employed to combine heart rate and blood pressure variability parameters to estimate BRS (the alpha index). Some authors have argued that BRS assessed at different frequencies of cardiovascular variabilities provide identical information and they should be combined into a single index of BRS based on total variability. The present study examined the relationship between BRS assessed using low, high, and total heart rate and blood pressure variabilities, and indices of cardiac vagal control assessed by standard spectral measures. Participants were 105 older male and female African-Americans who were part of the Healthy Aging In Nationally Diverse Longitudinal Samples (HANDLS) Study. Heart rate and blood pressure variabilities (HRV and BPV) were assessed using the Fast-Fourier Transform (FFT). The alpha index was computed as the square root of the ratio of low, high, or the mean of low and high frequency heart rate variability and the corresponding frequency ranges for systolic blood pressure variability. Correlations examining the relationships among BRS and various (e.g. log, normalized) indices of high frequency heart period variability (HF) were calculated for the total sample and by gender. Results indicated that the different BRS indices do not have the same relationship to all indices of HF. The results suggest that an aggregation of the power across bands is problematic at best, and indicates the need to examine the various frequency components separately.