Human baroreflex rhythms persist during handgrip and muscle ischaemia.

Abstract

To determine whether physiological, rhythmic fluctuations of vagal baroreflex gain persist during exercise, post-exercise ischaemia and recovery. We studied responses of six supine healthy men and one woman to a stereotyped protocol comprising rest, handgrip exercise at 40% maximum capacity to exhaustion, post-exercise forearm ischaemia and recovery. We measured electrocardiographic R-R intervals, photoplethysmographic finger arterial pressures and peroneal nerve muscle sympathetic activity. We derived vagal baroreflex gains from a sliding (25-s window moved by 2-s steps) systolic pressure-R-R interval transfer function at 0.04-0.15 Hz. Vagal baroreflex gain oscillated at low, nearly constant frequencies throughout the protocol (at approx. 0.06 Hz - a period of about 18 s); however, during exercise, most oscillations were at low-gain levels, and during ischaemia and recovery, most oscillations were at high-gain levels. Vagal baroreflex rhythms are not abolished by exercise, and they are not overwhelmed after exercise during ischaemia and recovery.