Effects of exercise pressor reflex activation on carotid baroreflex function during exercise in humans

1. This investigation was designed to determine the contribution of the exercise presser reflex to the resetting of the carotid baroreflex during exercise. 2. Ten subjects performed 3.5 min of static one-legged exercise (20% maximal voluntary contraction) and 7 min dynamic cycling (20 % maximal oxygen uptake) under two conditions: control (no intervention) and with the application of medical anti-shock (MAS) trousers inflated to 100 mmHg (to activate the exercise presser reflex). Carotid baroreflex function was determined at rest and during exercise using a rapid neck pressure/neck suction technique. 3. During exercise, the application of MAX trousers (MAX condition) increased mean arterial pressure (MAP), plasma noradrenaline concentration (dynamic exercise only) and perceived exertion (dynamic exercise only) when compared to control (P < 0.05). No effect of the MAX condition was evident at rest. The MAX condition had no effect on heart rate (HR), plasma lactate and adrenaline concentrations or oxygen uptake at rest and during exercise. The carotid baroreflex stimulus-response curve was reset upward on the response arm and rightward to a higher operating pressure by control exercise without alterations in gain. Activation of the exercise presser reflex by MAX trousers further reset carotid baroreflex control of MAP, as indicated by the upward and rightward relocation of the curve. However, carotid baroreflex control of HR was only shifted rightward to higher operating pressures by MAX trousers. The sensitivity of the carotid baroreflex was unaltered by exercise presser reflex activation. 4. These findings suggest that during dynamic and static exercise the exercise presser reflex is capable of actively resetting carotid baroreflex control of mean arterial pressure; however, it mould appear only to modulate carotid baroreflex control of heart rate.