Cardiovascular Function During Exercise and Hypovolemia
Increases in cardiac output and rate of blood flow to skeletal muscle are needed during exercise to meet the increased metabolic needs of the active skeletal muscle. several of the cardiovascular adjustments during exercise are learned responses or behavior responses that begin just prior to or at the initiation of exercise.
These are apparently initiated by the cerebral cortex, involve autonomic nerves, and include an increased heart rate and vasodilation of arterioles supplying skeletal muscle. increased circulating levels of epinephrine may also contribute to these changes. After exercise has begun, appropriate vasodilation of arterioles supplying active skeletal muscles is primarily maintained by local metabolites produced by the active muscles. Typically, the increase in cardiac function is greater than the degree of vasodilation, so arterial pressure rises slightly. Vascular resistance increases in other organs whose metabolism is not increased during exercise, and this prevents an increased blood flow to these organs. During exercise, the increased cardiac output (increased heart rate and contractility) is maintained by sympathetic stimulation of the heart. This sympathetic stimulation is primarily maintained by the mechanisms originating in the cerebral cortex and by reflexes based on afferent information originating in the exercising skeletal muscle.Hypovolemia is abnormally decreased circulating fluid volume (i.e., blood volume). it can occur rapidly, as a result of hemorrhage, or slowly, as a result of dehydration. Reduced blood volume results in reduced cardiac filling pressure and ventricular filling (i.e., reduced end-diastolic volume). Without adequate filling, sV falls, and therefore cardiac output can be insufficient to maintain capillary perfusion throughout the body. A severe reduction in cardiac output drastically lowers blood pressure, eliciting a strong response by the baroreceptor reflex. An accelerated heart rate is part of this response. The reduced cardiac output and the intense peripheral vasoconstriction resulting from the reflex response both contribute to the characteristic blanching of mucus membranes. The reduced stroke volume is the major cause of weakening of the pulse.