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.