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1 Department of Integrative Physiology, University of North Texas Health Science Center, Fort Worth, Texas, USA
* To whom correspondence should be addressed. E-mail: sogoh{at}hsc.unt.edu.
The purpose of this study was to examine the hypothesis that the operating point of the cardiopulmonary baroreflex resets to the higher cardiac filling pressure of exercise associated with the increased cardiac filling volumes. Eight men (means±SE: age 26±1 yr; height 180±3 cm; weight 86±6 kg) participated in the present study. Lower body negative pressure (LBNP) was applied at 8 and 16 Torr to decrease central venous pressure (CVP) at rest and during steady-state leg cycling at 50% VO2peak (104±20 W). Subsequently, two discrete infusions of 25% human serum albumin solution were administered until CVP was increased by 1.8±0.6 and 2.4±0.4 mmHg at rest, and 2.9±0.9 and 4.6±0.9 mmHg during exercise, respectively. During all protocols, HR, arterial blood pressure and CVP were recorded continuously. At each stage of LBNP or albumin infusion, forearm blood flow and cardiac output were measured. During exercise, forearm vascular conductance (FVC) increased from 7.5±0.5 to 8.7±0.6 U (P=0.024) and total systemic vascular conductance (TSVC) from 7.2±0.2 to 13.5±0.9 L/min/mmHg (P<0.001). However, there was no significant difference in the responses of both FVC and TSVC to LBNP and the infusion of albumin between rest and exercise. These data indicate that the cardiopulmonary baroreflex had been reset during exercise to the new operating point associated with the exercise induced change in cardiac filling volume.
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