Correlations between spectral measures of baroreflex sensitivity variability and HRV during supine position, paced breathing, standing and exercise

We assessed the relations between spectral and temporal measures of baroreflex sensitivity variability (BRSV) and heart rate variability (HRV) during four maneuvers that induce distinctive vagal activity. From the time-frequency distribution (TFD) of RR intervals (RR) and systolic arterial pressure (SAP), low-frequency power of RR (LF_RR), high-frequency power of RR (HF_RR), low-to-high-frequency ratio (LF_RR/HF_RR) and lowfrequency power of SAP (LF_SAP) were computed. BRS instantaneous values, obtained by the alpha index from the low-frequency band, can be separated into a nonfluctuating part, mean BRS (BRS_m), and a variable part, BRSV. The TFD of BRSV showed a single component in the very low-frequency band (VLF_BRS). Correlations of both HF_RR and mean RR (RR_m) with VLF_BRS and BRS_m ranged from 0.89 to 0.90. RR_m-BRS_m correlation was greater (p<;0.01) than the non-significant RR_m-LF_RR/HF_RR correlation (-0.38±0.39). BRS_m and VLF_BRS power are strongly correlated to each other and to vagal activity, and are better indexes of sympathovagal balance than the usual LF_RR/HF_RR ratio.