Effects of Two Types of Linearly Increased Isometric Exercise on Instantaneous Baroreflex and Respiratory Sinus Arrhythmia Sensitivities Computed by Alpha Index

摘要

To assess the linearity of the relation between muscular force (%MF) and baroreflex sensitivity (BRS), respiratory sinus arrhythmia sensitivity (RSAS) and their respective coherences (cBRS and cRSAS), 35 healthy subjects performed static handgrip (HG) or leg extension (LE) linearly increased until fatigue (LIF). From the time-frequency spectra of R-R intervals (RR), respiration (Res), systolic (SP) and diastolic pressures (DP) series, their instantaneous low-frequency (LFRR, LFSP, LFDP) and high-frequency (HFRR, HFRes) powers were estimated to compute, by alpha index, BRS and RSAS, as well as their time-frequency coherences. Relations of %MF with BRS, cBRS, RSAS and cRSAS were inverse, and those with heart rate (HR), DP and HFRes, were direct, all but RSAS with greater slopes and correlations in LE than HG. RSAS can be computed analogously to BRS by alpha index, and their coherences can be used as complementary measures of the degree of their input-output coupling. Performing HG and LE in a LIF format provokes moderately to strongly correlated effects, greater for LE than HG, consisting in progressive vagal withdrawal with loss of respiratory-cardiac modulation and release of sympathetic activity that cause the parallel increases of DP and HR with increasing regularity, greater for LE than HG.