Peripheral vascular resistance (PVR) is a measure of the resistance in the circulatory system that is used to create blood pressure. It is determined by the tension of the walls of the blood vessels and the amount of blood they can carry at any given time. The main control of PVR occurs in the arterioles, small branchlike vessels that connect larger arteries to the smaller vessels, the capillaries.
Anatomy of Arterioles
Arterioles are composed of three layers: a thick outer layer of smooth muscle, a thinner middle layer of connective tissue, and a thin inner layer of endothelial cells. The thick layer of smooth muscle is responsible for controlling the diameter of the arteriole, and thus the resistance to flow. This is regulated by the release of various chemicals such as epinephrine, noradrenaline, and nitric oxide.
The release of chemicals such as epinephrine and noradrenaline cause the arterioles to constrict, creating an increase in peripheral resistance. Conversely, nitric oxide causes the arterioles to relax, creating a decrease in resistance. This is an important aspect of the body’s homeostatic regulation, allowing the body to adjust to its environment and maintain a constant blood pressure.
Alterations in peripheral vascular resistance can have a variety of clinical implications. High peripheral vascular resistance is commonly seen in hypertension, a serious health condition that increases the risk of many cardiovascular diseases. Low peripheral vascular resistance can be seen in hypotension, which can lead to a number of complications such as dizziness and lightheadedness.
The main control of peripheral vascular resistance occurs in the arterioles, small vessels that connect the larger arteries to the smaller vessels, the capillaries. The release of various chemical substances such as epinephrine, noradrenaline, and nitric oxide can cause the arterioles to constrict or relax, creating an increase or decrease in peripheral resistance. High or low resistance can have serious clinical implications, and should be monitored closely.