Hyperemia is a condition in which blood congests in a particular area of the body. It can be either active or reactive.
Active hyperemia takes place during muscle contraction, which has earned it additional names, such a functional hyperemia and exercise hyperemia. Other causes include an increase in mental, cardiac, or gastrointestinal activity. With active hyperemia, blood collects in a particular organ as the result of increased blood flow caused by the arteriolar smooth muscle dilating, which is often due to an increase in the metabolism. When the metabolic activity of the organ is increased, it develops a decreased ability to vasodilate and to perform vascular recruitment. This is particularly true if a skeletal muscle is affected.
Active hyperemia becomes evident within seconds of increasing tissue metabolism, which also increases blood flow. This increased blood flow returns to normal when the metabolism is restored to normal. The severity of the condition is determined by the how much the metabolic activity is increased.
With reactive hyperemia, also referred to as passive hyperemia, blood collects in an organ of the body in response to a blockage in the veins that are supposed to move the blood out. This usually takes place after a person experiences a period of ischemia, such as arterial occlusion. This leads to a shortage of oxygen, as well as an increase in the amount of metabolic waste that builds up in the organ.
Reactive hyperemia can occur after a tourniquet is applied to a person’s limb and then removed. It can also occur when a person’s arterial vessels are clamped, such as during surgery, and then released. If a person undergoes coronary occlusions, such as those experienced with a coronary vasospasm, reactive hyperemia may result. Experiencing coronary occlusion for only a few brief seconds places high metabolic demands on the contracting myocardium, which results in pronounced blood congestion. The longer a person experiences coronary occlusion, the more severe the condition will be and the longer it will last.