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Medicine & Science in Sports & Exercise:
Symposium: Exercise Training and Orthostatic Intolerance: PDF Only

Effect of exercise training on cardiopulmonary baroreflex control of forearm vascular resistance in humans.

MACK, GARY W.; CONVERTINO, VICTOR A.; NADEL, ETHAN R.

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Abstract

MACK, G. W., V. A. CONVERTINO, and E. R. NADEL. Effect of exercise training on cardiopulmonary baroreflex control of forearm vascular resistance in humans. Med. Sci. Sports Exerc., Vol. 25, No. 6, pp. 722-726, 1993. We studied the stimulus-response characteristics of cardiopulmonary baroreflex control of forearm vascular resistance (FVR) in four groups of male volunteer subjects: i) unfit, ii) physically fit, iii) before and after 10 wk of endurance training (chronic blood volume expansion), and iv) before and after acute blood volume expansion. We assessed the relationship between reflex stimulus, i.e., changes in central venous pressure and response, i.e., FVR, during unloading of cardiopulmonary mechanoreceptors with lower body negative pressure (LBNP, 0 to -20 mm Hg). The slope of the linear relationship between FVR and CVP, the index of the responsiveness of this baroreflex, was significantly diminished (>50%) in the fit subjects compared with the unfit. The slope of the FVR-CVP relationship was inversely correlated with the subject's total blood volume, suggesting that blood volume expansion was related to the attenuated CP baroreflex. In the exercise training study, maximal oxygen consumption and blood volume increased following 10 wk of endurance training (N = 14) but were unchanged in the time control group (N = 7). The slope of the FVR-CVP relationship was significantly reduced (32%) following 10 wk of training but was unchanged in the time control group. The reduction in slope of the FVR-CVP relationship was inversely related to the increase in blood volume associated with exercise training. Acute blood volume expansion 8 ml.kg-1 body weight with 5% human serum albumin solution) significantly reduced the slope of the FVR-CVP relationship. These data support the hypothesis that the attenuated forearm vascular reflex in physically fit individuals is related to a training-induced hypervolemia. Training programs that increase maximal aerobic capacity but fail to elicit an increase in blood volume will have minimal effects on cardiopulmonary baroreflex control of FVR.

(C)1993The American College of Sports Medicine

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