Active Standing Test Provokes Different Effects on the Variability of Diastolic and Systolic Electromechanical Subintervals

We compared the effects of the active standing test (AST) on the variability of systolic (SRS), and diastolic (DSR) subintervals in 24 volunteers.The time courses of the low-frequency (LFRR, LFSRS, and LFDSR) and highfrequency powers (HFRR, HFSRS, HFDSR) of RR, SRS, and DSR series were computed using a time-frequency distribution.While the time courses of RR and DSR series displayed a sudden fall, SRS series showed a minuscule increase.Correlation of RR intervals with DSR, and SRS were 0.9960.004,and -0.3130.29,respectively.LFRR and LFDSR showed overshoots, with coherence of 0.9960.003,correlation of 0.9950.007,and LFDSR/LFRR of 1.100.07.LFSRS displayed very small overshoots, with LFSRS-LFRR coherence of 0.710.11,correlation of 0.640.22,and LFSRS/LFRR of 0.020.01.HFRR and HFDSR fell abruptly, with coherence of 0.9930.007,correlation of 0.9960.005,and HFDSR/HFRR of 1.210.13.HFSRS showed a small increment, with HFSRS-HFRR coherence of 0.670.13,correlation of 0.010.54,and HFSRS/HFRR of 0.020.01.Our findings support that the autonomic modulation of AST is exerted mainly on the DSR subinterval, with minimal impact on the SRS subinterval.The greater variability of DSR than RR in the low and high frequencies results from the combined modulatory effects of respiratory and vascular factors.