Exercise - Cardiovascular Homeostasis

Overview
  • Substantial changes in cardiovascular function are required to accommodate the physiological demands of intense physical exercise. The basic goals of this response are to increase cardiac output, selectively route that increased cardiac output to exercising muscles, and appropriately increase venous return to sustain the increased cardiac output.
Increased Cardiac Output
  • In response to the anticipation as well as the act of exercise, higher-order cerebral centers begin modulating the autonomic nervous system to increase cardiac output. This is achieved largely by increasing SNS tone which via processes discussed in autonomic cardiac regulation results in higher cardiac contractility as well as heart rate. Increased contractility boosts the heart's stroke volume and together with increased frequency of pumping, results in a substantial increase in total cardiac output. In addition, increased venous return (see below) results in increased Ventricular End Diastolic Volumes (VEDVs) and thus cardiac preload which directly boost cardiac output courtesy of the Frank-Starling Relationship.
Increased Venous Return
  • As is clear from cardiovascular function integration an increase in cardiac output naturally increases the venous return by causing a counter-clockwise rotation of the cardiac function curve. Additionally, SNS stimulation of veins results in their venoconstriction which correspondingly increases the "Mean Systemic Pressure" and thus the venous return as discussed in the vascular function curve Page. Finally, intense muscular activity results in intermittent squeezing of veins which promotes venous return as discussed in venous physiology. All of these factors together boost venous Return thus providing a sufficient rate of returning blood to sustain the heart's increased cardiac output.
Selective Routing
  • A primary goal during exercise is to selectively route the increased Cardiac Output toward exercising muscles and away from tissues not essential for the current physical exertion. Increased SNS tone results in wide-spread vasoconstriction of arterioles throughout the body. However, intrinsic mechanisms of local blood flow regulation override this vasoconstriction in the vasculature of exercising muscle and instead cause vasodilation. Consequently, vasoconstriction in most tissues reduces their blood flow; however, vasodilation in exercising muscles increases their blood flow. The overall effect of this is to selectively direct blood flow to exercising muscles and away from tissues not essential for maintaining increased physical activity