Beat-to-beat response patterns of spectral sympathetic estimators to the cold face test and their comparison to those of the active orthostatic test

We assessed the effects of cold face test (CFT) and active orthostatic test (AOT) on the RR intervals (RR), systolic pressure (SP) and maximal amplitude of arterial pressure first derivative (dmAP) time series of 25 healthy volunteers, and the instantaneous dynamics of their low-frequency powers (LFRR, LFSP and LFdmAP), to characterize their time course, and compare their performance as sympathetic markers as well as the magnitude of the sympathetic response evoked by each maneuver. All the variables studied displayed distinct instantaneous response patterns to each maneuver: while in CFT they increased to a plateau, in AOT they presented overshoots at the beginning and end of the test. In both tests, LFdmAP and LFSP dynamics were similar and strongly correlated, and presented a weak correlation with LFRR. Means of LFdmAP and LFSP in CFT were 7 times smaller than in AOT. Our findings support that LFSP and LFdmAP powers exhibit similar performance as noninvasive sympathetic markers and that all variables studied show distinctive beat-to-beat response patterns to each maneuver. Using the sympathetic response produced by AOT as reference, the one evoked by CFT is smaller.