Vascular tone

Of the Vascular tone corresponds to the general state of tension in the vascular muscles, which are responsible for blood circulation. The higher regulation is incumbent on the sympathetic, but local regulators are also available to the organism. Abnormal contractions of the vascular muscles are called vasospasms and can arise from various diseases.

What is vascular tone

The human blood system is equipped with muscles also known as the vascular muscles. The smooth vascular muscles give the vessels their tone. Every muscle has a basic tone. This is the state of tension that a body structure maintains even without actual arousal. The basic tone can thus be distinguished from the contraction that a muscle can actively undertake when it is excited. This contraction increases the tone and allows it to rise above the basic tone.

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The vascular tone is the basic state of tension that is present in the smooth vascular muscles without prior excitation or contraction. Changes in vascular tone automatically lead to changes in the vascular lumen.

An increase in tone causes vasodilation. A decrease leads to vasoconstriction in the lumen width. It therefore depends on the vascular tone how much blood can pass through the blood vessels per unit of time. The tone of the vascular muscles has an effect on the vascular resistance and the local blood flow. As the sum of serial resistances, the vascular tone is the total peripheral resistance, which significantly regulates blood pressure. The muscles are controlled by the autonomic nervous system.

Function & task

During vasoconstriction, the vascular muscles contract. This reduces the lumen of the vessels and the flow rate of the blood decreases. Vasodilation, on the other hand, occurs when the vascular muscles relax. The lumen increases and the blood flow increases. The tone of the vascular muscles thus determines the amount of blood that passes through the individual vessels.

The basic tone lies between vasoconstriction and vasodilation. In the resting state, the vascular muscles are neither completely relaxed nor actively contracted, but rather have a basic tone. The vascular tone depends on various influencing factors that have a regulatory effect on blood pressure. One of these influencing variables is the tone of the sympathetic nervous system. This part of the autonomic nervous system determines the state of excitement of the nervous system. The sympathetic has a vasoconstrictive effect on the vessels and is responsible for their alkaline toning through this influence. When the sympathetic is inhibited, it affects the vascular tone. The inhibition of the permanently toning sympathetic nervous system leads to vasodilation.

In addition to the tone of the sympathetic nervous system, hormones such as the stress hormone adrenaline and substances such as angiotensin II or vasopressin influence the tone of the vascular muscles.

In addition, the vascular muscles have local regulatory mechanisms. These include the Bayliss effect and the Euler-Liljestrand mechanism. The Bayliss effect corresponds to a mechanism for maintaining constant organ blood flow despite changing blood pressure values. The Euler-Liljestrand mechanism results in a reflex vasoconstriction of the pulmonary arterial vessels in hypoxia.

In addition, endothelial factors affect vascular tone. These include, for example, NO, prostaglandin E2 and prostacyclin. In addition, tissue metabolites such as H + ions or adenosine also have effects on the vascular tone and thus automatically on the prevailing blood pressure.

Illnesses & ailments

One of the most well-known diseases with a pathological vascular tone is the so-called angina pectoris. This is a seizure-like pain in the chest area that is triggered by a brief circulatory disorder in the heart and usually occurs as part of coronary heart disease. The special form of Prinzmetal's angina in particular is associated with a pathological vascular tone. The associated ischemia of the myocardium is caused by a spasm of the coronary artery. The seizure can last anywhere from seconds to minutes. The spastic narrowing of the artery occurs most frequently in the context of more or less severe stress on the body or the psyche.

Basically, all of the body's vessels can be affected by spastic contractions and their lumen can be greatly reduced during these seizure-like phenomena, which results in reduced blood flow in the local tissue.

All spasms of the vessels are summarized under the term vasospasm. This expression is associated with a sudden, spasmodic constriction of blood vessels that is triggered by a certain stimulus. Such phenomena in the brain are known as cerebral vasospasms and can sometimes have life-threatening consequences. They are often a complication of subarachnoid hemorrhage or a symptom of neurological disorders.

These pathological changes in vascular tone are also conceivable after certain types of poisoning, especially in connection with cocaine and methamphetamine use. When bleeding occurs, the blood that has entered breaks down in the subarachnoid space, releasing vasoconstrictive substances. Since the consequence of cerebral vasospasms causes the insufficient supply of parts of the brain with blood and oxygen, a common consequence of the phenomenon is secondary stroke. Since the sympathetic nervous system regulates the vascular tone, pathological vascular tones can in principle also be traced back to anomalies in this brain region.

Raynaud's syndrome is an example of this. The condition makes patients' fingers or toes pale due to vasospasm. The body minimizes heat loss when exposed to cold by stimulating the autonomic nervous system. This process directs more blood to the deeper veins of the body. In Raynaud's syndrome, this process is affected by dysregulation, which occurs primarily in the sympathetic part of the autonomic nervous system and which, through alpha-adrenoreceptors, leads to excessive vascular constriction of all end arteries.