Diminished baroreflex control of forearm vascular resistance following training

MACK, G. W., C. A. THOMPSON, D. F. DOERR, E. R. NADEL, and V. A. CONVERTINO. Diminished baroflex control of forearm vascular resistance following training. Med. Sci. Sports Exerc., Vol. 23, No. 12, pp. 1367–1374, 1991. The stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR units in mm Hg·min.100 ml·min-1) were studied in 14 volunteers before and after 10 wk of endurance training. We assessed the relationship between reflex stimulus (changes in central venous pressure, CVP) and response (FVR) during unloading of cardiopulmonary baroreceptors with lower body negative pressure (LBNP, 0 to −20 mm Hg). Changes in CVP during LBNP were estimated from pressure changes in a large peripheral vein in the dependent arm of the subject in the right lateral decubitus position. Maximal oxygen uptake (V̇2max) and total blood volume increased with endurance training from 37.8 ± 1.4 ml·min-1 ·kg-1 and 63.6 ± 2.1 ml kg-1 to 45.3 ± 1.4 ml·min-1 ·kg-1 and 69.3 ± 2.8 ml·kg-1, respectively (P < 0.05). Reflex forearm vasoconstriction occurred in response to a reduction in estimated CVP, and the absolute change in FVR per unit of CVP was reduced from −5.96 ± 0.79 to −4.06 ± 0.52 units.mm Hg-1 (P < 0.05) following exercise training bat was unchanged from −6.10 to 0.57 to −6.22 ± 0.94 units.mm Hg-1 for the time control group (N = 7). Resting values for FVR were similar before and after exercise training; however, resting estimated CVP was elevated from 9.5 ± 0.5 mm Hg before training to 11.3 ± 0.6 mm Hg after training. The reduction in sensitivity of the cardiopulmonary baroreflex control of FVR was linearly related to the increase in blood volume (r = 0.65, P < 0.05), suggesting that diminished cardiopulmonary baroreflex control of FVR in physically fit individuals is related, in part, to a training-induced Mood volume expansion.