Regulation of central blood volume and cardiac filling in endurance athletes: the Frank-Starling mechanism as a determinant of orthostatic tolerance.
Orthostatic intolerance may result from either an abnormally large postural decrease in central blood volume, cardiac filling pressures, and stroke volume, or inadequate neurohumoral responses to orthostasis. Endurance athletes have been reported as having a high incidence of orthostatic intolerance, which has been attributed primarily to abnormalities in baroreflex regulation of heart rate and peripheral resistance. In this review, we present evidence that athletes also have structural changes in the cardiovascular system that although beneficial during exercise, lead to an excessively large decrease in stroke volume during orthostasis and contribute to orthostatic intolerance. A unifying hypothesis based on cardiac mechanics that may explain the divergence of findings in conditions such as bed rest or spaceflight, and short- and long-term endurance training is presented.
Levine
B D
BD
Institute for Exercise and Environmental Medicine, Presbyterian Hospital, University of Texas Southwestern Medical Center, Dallas 75235.
D000222:Adaptation, Physiological; D001810:Blood Volume / Q000502:physiology*; D002302:Cardiac Output / Q000502:physiology*; D006801:Humans; D010806:Physical Education and Training; D010807:Physical Endurance / Q000502:physiology*; D010809:Physical Fitness / Q000502:physiology; D011187:Posture / Q000502:physiology*; D013318:Stroke Volume / Q000502:physiology; D016277:Ventricular Function, Left / Q000502:physiology