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Received November 17, 2006
Revised January 4, 2007
Accepted after revision February 18, 2007
1 University of North Texas Health Science Center
2 University of Missouri
3 UNTHSC
* To whom correspondence should be addressed. E-mail: sogoh{at}hsc.unt.edu.
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 vs. upright) and 2) pedal frequency (80 vs. 60 revolutions per minute (rpm)); while oxygen uptake (VO2) was kept constant. Eight male subjects performed three exercise trials: upright cycling at 60 rpm (Control); supine cycling at 60 rpm (SupEX) and upright cycling at 80 rpm 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 VO2 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.
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