Comparison of baroreflex sensitivity with a fall and rise in blood pressure induced by the valsalva manoeuvre

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 BRSvagal_inc (BRS_vagal derived from the rise in BP during phases III-IV of the Valsalva manoeuvre), to assess the association between BRSvagal_inc and BRSvagal_dec (BRS_vagal derived from the preceeding BP decrement) and to validate BRSvagal_inc 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). BRSvagal_inc and BRSvagal_dec 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. BRSvagal_inc was calculated in all subjects and correlated highly with BRSvagal_dec (r =0.72, P<0.001). BRSvagal_inc also correlated significantly with BP changes during phases II and IV of the Valsalva manoeuvre and sympathetic barosensitivity. BRSvagal_inc 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.