Microvascular Regulation: Normal Function and Disturbance in Disease

Abstract

An understanding of the disturbance of microvascular regulation requires first that we understand the normal state. Our current understanding of normal regulation has developed slowly over many years. The earliest view of the regulation of the peripheral circulation was that blood flow to the tissues was determined essentially by sympathetic constriction of arterial vessels and by arterial perfusion pressure. To the extent that the special needs of organs for increased blood flow were recognized (such as skeletal muscle in exercise), it was thought that neurally mediated local vasodilation was responsible. Shunting of flow among organs according to local needs was also hypothesized. For example, the vasoconstriction of skin blood vessels observed during mental activity was thought to increase total peripheral resistance by activation of the sympathetic nervous system, increasing arterial pressure, and, thereby, forcing more blood through the brain [1]. A few workers such as Roy and Brown [2] did suggest that locally produced metabolities such as carbon dioxide and hydrogen ions may cause vasodilation in special circumstances such as exercise and reactive hyperemia. But there was an overriding emphasis on the central regulation of all aspects of peripheral circulatory function.