Balance between sympathetic response to head-up tilt and cardiac vagal factors in healthy humans.

We evaluated the association between cardio-vagal baroreflex sensitivity (BRS; assessed with modified Oxford technique) and catecholamine response to 5 min 60 degrees head-up tilt (HUT) in 46 young healthy adults. HUT increased HR, mean arterial pressure, and NE (P < 0.05 for all). BRS was negatively correlated with NE response to HUT (r = -0.36, P < 0.05), suggesting that subjects with high vagal modulation (high BRS) require less sympathetic response (NE) to maintain normotension during orthostatic stress.