Vascular tone is a medical term used to describe the diameter and tone of a blood vessel when the vessel is fully dilated. Under normal conditions, all blood vessels experience at least a mild degree of contraction of the smooth muscles of the vessel. These contractions are used to determine vascular tone. When this tone is normal, the blood vessels are considered to be functioning at optimal levels. When these contractions become abnormal, vascular health may become compromised, requiring a trip to a medical professional for proper diagnosis and treatment.
Both types of blood vessels, arteries and veins, are considered when measuring vascular tone. An artery is a blood vessel which carries clean blood from the heart to the various tissues and organs of the body. A vein is a type of blood vessel responsible for transporting blood back to the heart after the tissues and organs have obtained the oxygen and nutrients from the blood.
Vascular tone naturally differs among organs. This is due to the differences in vasodilatory capacity. This means that the organs receiving a faster flow of blood will have a higher tone than the organs receiving a slower flow of blood. The myocardium, for instance, is the thickest of the heart muscles and has a high vascular tone. On the contrary, the kidneys and other renal organs have a much lower tone.
While there are several factors which can have an effect on vascular tone, these factors are generally divided into two categories. Extrinsic factors are those which begin outside of the tissue or organ where the blood vessel is found, such as blood flow regulation by the sympathetic nerves. Intrinsic factors are those which begin either in the actual blood vessel itself or in tissues immediately surrounding the vessel; chemicals or hormones produced by an organ that affect blood flow or blood pressure are intrinsic factors.
Certain medical conditions, including heart disease or high blood pressure, have the potential of causing vascular tone dysfunction. When this type of dysfunction is suspected, medical intervention becomes very important. Routine medical testing is often able to detect a problem before it turns into a life-threatening situation. In many cases, a combination of dietary changes and prescription medications are sufficient to restore proper vascular health. Surgical intervention sometimes becomes necessary, depending upon the patient's overall health.