Wada, Naoki

The baroreflex plays a key role in human BP (blood pressure) regulation. Its efferent limb consists of a vagal and a sympathetic component. The Valsalva manoeuvre is widely used to quantify vagal baroreflex function [BRS_vagal (vagal baroreflex sensitivity)], but most studies have focused on the R–R interval response to BP decrement, even though the subsequent response to an increment in BP is important and different. In the present study, we sought to evaluate whether BRS_vagal can be determined from BRSvagalinc (BRS_vagal derived from the rise in BP during phases III–IV of the Valsalva manoeuvre), to assess the association between BRSvagalinc and BRSvagaldec (BRS_vagal derived from the preceeding BP decrement) and to validate BRSvagalinc as an index of autonomic function. We studied patients with severe autonomic failure (n=49, 25 female), mild autonomic failure (n=25, 11 female) and matched normal controls (n=29, 15 female). BRSvagalinc and BRSvagaldec were calculated as the regression slope of R–R interval and systolic BP during phases III–IV and the early phase II of the Valsalva manoeuvre respectively, and compared these with other autonomic indices across the groups. BRSvagalinc was calculated in all subjects and correlated highly with BRSvagaldec (r=0.72, P<0.001). BRSvagalinc also correlated significantly with BP changes during phases II and IV of the Valsalva manoeuvre and sympathetic barosensitivity. BRSvagalinc was significantly different between the groups, being highest in the controls and lowest in patients with severe autonomic failure. In conclusion, vagal BRS, determined by relating R–R interval with the BP increase following phase III, is a valuable autonomic index, provides additional information about vagal baroreflex function and reflects overall severity of autonomic failure.

ABSTRACTIntroduction: The Valsalva maneuver (VM) is used widely to quantify the sensitivity of the vagal baroreflex loop (vagal baroreflex sensitivity, BRS_v), but most studies have focused on the heart rate (HR) response to blood pressure (BP) decrement (BRS_v↓), even though the subsequent response to an increment in BP after the VM (BRS_v↑) is important and different. Methods: We evaluated recordings of HR and BP in 187 normal subjects during the VM and determined both BRS_v↑, as determined by relating HR to the BP increase after phase III and BRS_v↓. Results: BRS_v↑ was related inversely to age. In addition, BRS_v↓, age, and magnitude of phase IV were independent predictors of BRS_v↑ in a multivariate model, accounting for 47% of the variance of BRS_v↑. Conclusions: The results indicate that both BRS_v↑ and BRS_v↓ become blunted with increasing age and that these indices relate to each other. Muscle Nerve 50: 535–540, 2014