Instantaneous Time-Courses of Baroreflex Sensitivity, Sympathetic and Vagal Activities in Response to Valsalva Maneuver

Salvador Carrasco-Sosa and Alejandra Guillén-Mandujano
Universidad Autónoma Metropolitana-I


The Valsalva maneuver (VM) effects on RR intervals (RR), systolic (SBP), and diastolic (DBP) blood pressure time series have been extensively characterized, unlike the VM effects on the time-courses of autonomic spectral indexes and baroreceptor sensitivity (BRS), for which no studies were identified. Thus, because of the physiological and clinical relevance of BRS and VM, we assessed, in 59 valid recordings of healthy young volunteers, the effects provoked by VM (40mmHg for 20s) on the 140-s-instantaneous time-courses of the low-frequency components of RR (LFRR), SBP (LFSBP), DBP (LFDBP), the high-frequency component of RR (HFRR), estimated by a time-frequency distribution, BRS computed by alpha index (√(LFRR/LFSBP)) and its coherence (BRSCO) obtained by cross-time frequency analysis. Ensemble averages of BRS, LFRR, LFSBP, LFDBP, and HFRR dynamics showed similar response patterns in each phase of VM, relative to baseline: decreased in early phase II (IIe), LFSBP, and LFDBP after an initial increment; raised progressively in late phase II (IIL), except HFRR which remained reduced and recovered at the end; peaked in phase IV, LFRR and LFSBP in the early part, and BRS and HFRR in the late part. Mean phase-IV-to-phase-IIL ratios (IV/IIL) of BRS, LFRR, LFSBP, HFRR, and RR (Valsalva ratio), ranged from 1.4±0.2 to 7.0±2.1. The table shows the means of BRS and BRSCO in VM phases, and the BRS IV/IIL ratio. Our findings support that: while the moderate effects of SBP increment and RR reduction in phase IIL are associated with moderate effects of BRS and vagal activity reductions and to sympathetic activity increment, in phase IV the large SBP and RR increments are associated with large peaks of BRS, sympathetic and vagal activities. The similarity between the IV/IIL ratios of BRS and spectral autonomic indexes, suggests that BRS changes possibly drive their patterned response to VM, including the Valsalva ratio.