CONVERTINO, V. A. Baroreflex-Mediated Heart Rate and Vascular Resistance Responses 24 h after Maximal Exercise. Med. Sci. Sports Exerc., Vol. 35, No. 6, pp. 970–977, 2003.
Plasma volume, heart rate (HR) variability, and stimulus-response relationships for baroreflex control of forearm vascular resistance (FVR) and HR were studied in eight healthy men after and without performing a bout of maximal exercise to test the hypotheses that acute expansion of plasma volume is associated with 1) reduction in baroreflex-mediated HR response, and 2) altered operational range for central venous pressure (CVP).
The relationship between stimulus (ΔCVP) and vasoconstrictive reflex response (ΔFVR) during unloading of cardiopulmonary baroreceptors was assessed with lower-body negative pressure (LBNP, 0, −5, −10, −15, −20 mm Hg). The relationship between stimulus (Δmean arterial pressure (MAP)) and cardiac reflex response (ΔHR) during loading of arterial baroreceptors was assessed with steady-state infusion of phenylephrine (PE) designed to increase MAP by 15 mm Hg alone and during application of LBNP (PE+LBNP) and neck pressure (PE+LBNP+NP). Measurements of vascular volume and autonomic baroreflex responses were conducted on two different test days, each separated by at least 1 wk. On one day, baroreflex response was tested 24 h after graded cycle exercise to volitional exhaustion. On another day, measurement of baroreflex response was repeated with no exercise (control). The order of exercise and control treatments was counterbalanced.
Baseline CVP was elevated (P = 0.04) from a control value of 10.5 ± 0.4 to 12.3 ± 0.4 mm Hg 24 h after exercise. Average ΔFVR/ΔCVP during LBNP was not different (P = 0.942) between the exercise (−1.35 ± 0.32 pru·mm Hg−1) and control (−1.32 ± 0.36 pru·mm Hg−1) conditions. However, maximal exercise caused a shift along the reflex response relationship to a higher CVP and lower FVR. HR baroreflex response (ΔHR/ΔMAP) to PE+LBNP+NP was lower (P = 0.015) after maximal exercise (−0.43 ± 0.15 beats·min−1·mm Hg−1) compared with the control condition (−0.83 ± 0.14 beats·min−1·mm Hg−1).
Expansion of vascular volume after acute exercise is associated with altered operational range for CVP and reduced HR response to arterial baroreceptor stimulation.
U.S. Army Institute of Surgical Research, Fort Sam Houston, TX
Address for correspondence: Victor A. Convertino, Ph.D., U.S. Army Institute of Surgical Research, 3400 Rawley E. Chambers Avenue, Building 3611, Fort Sam Houston, TX 78234-6315; E-mail: firstname.lastname@example.org.
Submitted for publication September 2002.
Accepted for publication January 2003.