perfusion perfusion perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. perfusion is measured as the rate at which blood is delivered to tissue, or volume of blood per unit time (blood flow) per unit tissue mass. the si unit is m3/(s·kg), although for human organs perfusion is typically reported in ml/min/g. the word is derived from the french verb "perfuser" meaning to "pour over or through". all animal tissues require an adequate blood supply for health and life. poor perfusion (malperfusion), that is, ischemia, causes health problems, as seen in cardiovascular disease, including coronary artery disease, cerebrovascular disease, peripheral artery disease, and many other conditions. a lindbergh perfusion pump, c. 1935, an early device for simulating natural perfusion tests verifying that adequate perfusion exists are a part of a patient's assessment process that are performed by medical or emergency personnel. the most common methods include evaluating a body's skin color, temperature, condition (dry/soft/firm/swollen/sunken/etc), and capillary refill. during major surgery, especially cardiothoracic surgery, perfusion must be maintained and managed by the health professionals involved, rather than left to the body's homeostasis alone. as the lead surgeons are often too busy to handle all hemodynamic control by themselves, specialists called perfusionists manage this aspect. there are more than one hundred thousand perfusion procedures annually. discovery in 1920, august krogh was awarded the nobel prize in physiology or medicine for his discovering the mechanism of regulation of capillaries in skeletal muscle. krogh was the first to describe the adaptation of blood perfusion in muscle and other organs according to demands through the opening and closing of arterioles and capillaries. malperfusion malperfusion can refer to any type of incorrect perfusion though it usually refers to hypoperfusion. the meaning of the terms "overperfusion" and "underperfusion" is relative to the average level of perfusion that exists across all the tissues in an individual body. perfusion levels also differ from person to person depending on metabolic demand. examples follow: heart tissues are considered overperfused because they normally are receiving more blood than the rest of tissues in the organism; they need this blood because they are constantly working. in the case of skin cells, extra blood flow in them is used for thermoregulation of a body. in addition to delivering oxygen, blood flow helps to dissipate heat in a physical body by redirecting warm blood closer to its surface where it can help to cool a body through sweating and thermal dissipation. many types of tumors, and especially certain types, have been described as "hot and bloody" because of their overperfusion relative to the body overall. overperfusion and underperfusion should not be confused with hypoperfusion and hyperperfusion, which relate to the perfusion level relative to a tissue's current need to meet its metabolic needs. for example, hypoperfusion can be caused when an artery or arteriole that supplies blood to a volume of tissue becomes blocked by an embolus, causing either no blood or at least not enough blood to reach the tissue. hyperperfusion can be caused by inflammation, producing hyperemia of a body part. malperfusion, also called poor perfusion, is any type of incorrect perfusion. there is no official or formal dividing line between hypoperfusion and ischemia; sometimes the latter term refers to zero perfusion, but often it refers to any hypoperfusion that is bad enough to cause necrosis. measurement