Effects of moderate exercise training on plasma volume, baroreceptor sensitivity and orthostatic tolerance in healthy subjects

Abstract

The effect of physical training on an individual's ability to withstand an orthostatic stress is unclear. This study was undertaken to determine the effects on orthostatic tolerance in healthy volunteers of training at a level appropriate for unfit subjects and cardiorespiratory patients. In 11 asymptomatic, untrained subjects the following assessments were made: plasma volume by Evans Blue dye dilution and blood volume derived from haematocrit; carotid baroreceptor sensitivity from the slope of the regression of change in cardiac interval against pressure applied to a neck chamber; orthostatic tolerance as time to presyncope in a test of head-up tilting combined with lower body suction; exercise test relating heart rate to oxygen consumption. Subjects were then given a training schedule (.5BX/XBX, Royal Canadian Air Force) involving 11-12 min of mixed exercises per day until an age/sex related 'target' was reached. Following training all subjects showed evidence of improved fitness, seen as decreases in heart rate at an oxygen uptake (V0J of 1.5 1 min-' and in the elevation of the regression line between hearr rate and Vo,. All also had increases in plasma and blood volumes and decreases in baroreceptor sensitivity. Seven of the subjects showed increases in orthostatic tolerance. Improvement in orthostatic tolerance was related to a low initial tolerance, and was associated with increases in plasma volume and decreases in baroreceptor sensitivity. These results show that moderate exercise training increases orthostatic tolerance in subjects who do not already have a high initial tolerance and suggest that training may be of value in the management of untrained patients with attacks of syncope due to orthostatic intolerance.

Does non-pharmacological treatment affect outcomes in dysautonomic syndromes?

“…The active "muscle pump" in the legs, help venous blood return, preventing venous pooling. The stronger the muscle pump, the better [23,24]. Physical training also induces modifications in the autonomic nervous system, increasing parasympathetic activity to the heart, lowering HR and improving baroreflex sensitivity [24,25].…”

Arterial blood pressure response to head-up tilt test and orthostatic tolerance in nurses

“…First, we did not evaluate the physical fitness of the subjects, which can affect orthostatic tolerance [45]; thus, we did not measure Vo 2max . Second, we did not measure blood volume, which also affects orthostatic tolerance [11,12]. Given that physical training may increase blood volume, moderately fit persons should attain a higher tolerance to orthostasis because of a large blood volume [11].…”

“…Second, we did not measure blood volume, which also affects orthostatic tolerance [11,12]. Given that physical training may increase blood volume, moderately fit persons should attain a higher tolerance to orthostasis because of a large blood volume [11]. Third, we used the sequence method for evaluating BRS, which is safety for human subjects and appropriate to use in field studies because it measures noninvasively under resting conditions.…”

“…Improvement in orthostatic tolerance is achieved by improving orthostatic cardiovascular responses [10]. For example, exercise training (moderate, but not severe) can improve orthostatic tolerance [11]; the underlying mechanism is assumed to involve increased blood volume [11,12], reduced leg venous compliance [13], and an altered baroreflex function [11,13].…”

Predicting metabolic rate from heart rate in juvenile Steller sea lionsEumetopias jubatus

“…O∑ relationship. As fitness improves, the heart enlarges, ventricular stretching is enhanced, and blood volume increases, resulting in an increased stroke volume, allowing reduction in the heart rate for a given oxygen consumption relative to that of more sedentary individuals (Swaine et al, 1992;Plowman and Smith, 1997;Mtinangi and Hainsworth, 1999).…”