Cardiovascular and renal function during exercise-induced blood volume expansion in men

Abstract

To test the hypothesis that reduced baroreflex sensitivity is a direct result of exercise, we measured forearm vascular conductance (FVC) responses to graded lower body negative pressure (LBNP) 2, 20, and 44 h after intense exercise. Eight 4-min bouts of exercise at 85% of maximum oxygen uptake produced 3.5 +/- 0.7 and 3.9 +/- 1.0% blood volume (BV) expansions at 20 and 44 h of recovery, respectively. BV was unchanged from control values 2 h after exercise. The reduction in FVC was significantly less than control values during 30 and 40 mmHg of LBNP at 2 and 20 h of recovery, respectively, whereas heart rate and cardiac stroke volume responses were unchanged. Thus, a reduced FVC response to LBNP preceded BV expansion, demonstrating that exercise itself can elicit an attenuation of baroreflex function. To test the hypothesis that volume sensitivity of renal function is attenuated by intense exercise, we measured cardiovascular variables, plasma hormone concentrations, and renal output. At 20 h of recovery, resting mean arterial blood pressure and cardiac output were increased by 6 +/- 1 mmHg and 0.6 +/- 0.2 l/min, respectively, but resting plasma aldosterone and overnight Na+ excretion rate were unchanged. At 44 h of recovery, plasma aldosterone was decreased by 26 +/- 9% and overnight Na+ excretion rate was increased by 51 +/- 26%. Thus, appropriate endocrine and renal responses to increased BV were delayed until 44 h of recovery. Our findings suggest that a postexercise attenuation of baroreflex function participates in the induction of BV expansion by intense exercise.

Blood Volume Expansion and Cardiorespiratory Function: Effects of Training Modality

“…The maintenance of an elevated EDV and BV over the duration of the training period with minor changes in the resting concentrations of the volume-regulating hormones may also indicate that the pressure mechanisms controlling the volume-regulating hormones (e.g., low pressure cardiopulmonary baroreceptors) are altered by training as supported by the findings of other investigators (7,15).…”

“…Investigators have consistently shown the ability of endurance-trained individuals to maintain a chronically expanded BV (2,8,14). This is associated with a compensatory attenuation in the volume-regulatory reflex mechanisms (1,5,7).…”

Impact of sex and chronic resistance training on human patellar tendon dry mass, collagen content, and collagen cross-linking

“…The evening meal (Ensure Plus, Ross, Columbus, OH) provided 50% of the subjects' estimated daily caloric need (16) and standardized the composition, amount, sodium content, and timing of the final prebiopsy meal. Subjects also followed guidelines (11,18,43) to standardize the influence of hydration status on tissue fluid balance: ad libitum water consumption during the 3 days before their experimental trial, 1 liter of water between 4 PM and bedtime on the evening before their trial, and a standardized amount of water (7 ml/kg body wt) 1 h before arrival at the laboratory. For standardization of the impact of estrogen and progesterone levels on water balance (11,48,49), all women completed their trial during days 3-7 of their menstrual cycle as reported by the subject.…”

Cardiovascular Responses to Lower Body Negative Pressure in the Elderly: Role of Reduced Leg Compliance

“…The SV was estimated by impedance cardiography (model 304B apparatus; Surcom, Minneapolis, Minn., USA) using the standard four-band electrode arrangement as described elsewhere [18]. A prior study [19] indicated that ¢SV and delta central venous pressure estimated by measuring the peripheral venous pressure showed a strong linear relationship, so ¢SV was used as an indicator of baroreceptor unloading with delta central venous pressure.…”