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.