Increases in central blood volume modulate carotid baroreflex resetting during dynamic exercise in humans

We sought to determine if resetting of the carotid-vasomotor baroreflex function curve during exercise is modulated by changes in central blood volume (CBV). CBV was increased during exercise by altering: (1) subject posture (supine versus upright) and (2) pedal frequency (80 versus 60 revolutions min(-1) (r.p.m.)); while oxygen uptake ( ) was kept constant. Eight male subjects performed three exercise trials: upright cycling at 60 r.p.m. (control); supine cycling at 60 r.p.m. (SupEX) and upright cycling at 80 r.p.m. to enhance the muscle pump (80EX). During each condition, carotid baroreflex (CBR) function was determined using the rapid neck pressure (NP) and neck suction (NS) protocol. Although mean arterial pressure (MAP) was significantly elevated from rest (88 +/- 2 mmHg) during all exercise conditions (P < 0.001), the increase in MAP was lower during SupEX (94 +/- 2 mmHg) and 80EX (95 +/- 2 mmHg) compared with control (105 +/- 2 mmHg, P < 0.05). Importantly, the blood pressure responses to NP and NS were maintained around these changed operating points of MAP. However, in comparison to control, the carotid-vasomotor baroreflex function curve was relocated downward and leftward when CBV was increased during SupEX and 80EX. These alterations in CBR resetting occurred without any differences in or heart rate between the exercise conditions. Thus, increasing CBV and loading the cardiopulmonary baroreflex reduces the magnitude of exercise-induced increases in MAP and CBR resetting. These findings suggest that changes in cardiopulmonary baroreceptor load influence carotid baroreflex resetting during dynamic exercise.