Your body undergoes physiologic changes during exercise so that your working muscles receive enough oxygenated blood to sustain strenuous activity. The blood vessels will either widen to allow greater flow to a specific area or narrow to redirect the blood flow to the necessary muscles. With vascular disease, one or more vessels are narrowed or blocked by plaque. This impedes blood flow to essential muscles, namely the heart, and can lead to chest pain or sudden cardiac arrest.
Vasodilation
The active muscles will rapidly consume oxygen during exercise. To replenish the oxygen, the muscles produce byproducts such as adenosine and carbon dioxide, which prompt the blood vessels in that area to dilate or expand. This vasodilation will allow a greater amount of oxygenated blood to be delivered to the muscles. In a healthy body, vasodilation will take place in the coronary blood vessels, those surrounding the heart, and the skin and muscle's blood vessels.
Vasoconstriction
Because extra oxygenated blood is needed in the exercising muscles, the blood must be taken from the inactive tissues of the body such as the abdomen and kidneys. Your sympathetic nervous system, part of the brainstem and spinal cord, will stimulate the blood vessels to constrict, or narrow, reducing blood flow to those tissues. The blood flow is then redistributed to the active muscles.
Competing Reactions
You may wonder how the sympathetic nervous system can only command the blood vessels of nonessential tissues to constrict while leaving the working muscles untouched. The sympathetic response causes a widespread vasoconstriction throughout your whole body. However, the chemical byproducts produced by the working muscles override this response where necessary. A 2004 report published in the "Journal of Physiology" demonstrates that the circulating byproducts play a role in oxygen delivery regulation by inducing vasodilation and blunting the sympathetic vasoconstrictor activity.
Impaired Responses
In people with conditions such as heart or vascular disease, the blood vessels may not respond appropriately during exercise. For instance, if you have a blockage in one or more of the heart vessels, vasodilation could be impaired, making the heart muscle deficient of oxygenated blood and possibly causing symptoms such as chest pain. Similarly, peripheral vascular disease can cause lesions in the blood vessels of the limbs that prevent adequate perfusion, or blood flow. To remedy these conditions, physicians may prescribe medications called vasodilators that will artificially widen the vessels. More invasive surgical procedures also may be an option.
References
- "Essentials of Exercise Physiology, 3rd Edition"; William D. McArdle, et al.; 2006
- "Journal of Clinical Investigation"; Endogenous Adenosine Mediates Coronary Vasodilation During Exercise After K(ATP)+ Channel Blockade; D.J. Duncker, et al.; January 1995
- "Journal of Applied Physiology"; Sympathetic Vasoconstriction in Active Skeletal Muscles During Dynamic Exercise; John B. Buckwalter, et al.; July 1997.
- "Journal of Physiology"; Circulating ATP-Induced Vasodilatation Overrides Sympathetic Vasoconstrictor Activity in Human Skeletal Muscle; Jaya B. Rosenmeier, et al.; 2004
