Instantaneous response patterns of baroreflex sensitivity, respiratory sinus arrhythmia sensitivity and vagal activity to cold face test and active orthostatic test

In 25 healthy volunteers, we examined if active orthostatic test (AOT) and cold face test (CFT) cause opposite effects on the instantaneous dynamics of baroreflex sensitivity (BRS), high-frequency power of RR intervals (HF
_RR
), low-frequency power of systolic pressure (LF
_SP
), LF
_RR
/HF
_RR
ratio and respiratory sinus arrhythmia sensitivity RSAS), obtained by a time-frequency distribution. We also assessed the correlations between BRS and the spectral measures of autonomic activity. Instantaneous values of RR, HF
_RR
, BRS and RSAS presented characteristic response patterns of overshoot in CFT, and of undershoot of the four variables in AOT. BRS was positively correlated with HF
_RR
(0.85±0.14), RSAS (0.76±0.11) and RR (0.87±0.11), and negatively with LFsp (-0.81±0.09) and LFrr/HFrr (-0.77±0.13). In a beat-to-beat format BRS, HFrr, RSAS, LF
_SP
and RR: exhibit great dynamism, are strongly correlated, and follow distinctive opposite patterns in response to each maneuver. While in CFT the greater values of BRS and RSAS allow amplifying the vagal activity and minimizing the sympathetic outflow, in AOT the lower values of BRS and RSAS determine the opposite autonomic effects. The tight correlations suggest that both BRS and RSAS operate to reciprocally strengthen and inhibit the sympathetic and vagal activities.