Autoregulation of blood flow, the tendency for blood flow to remain constant despite changes in arterial perfusion pressure, is a ubiquitous and much studied phenomenon. Autoregulation of blood flow refers to the adjustment of blood flow due to metabolic activity of supplied tissues, and the maintaining of constant blood flow during constant tissue activity by changing perfusion pressure. Regulation of blood flow is most easily understood with a constant level of tissue activity and examining the way perfusion, or arterial pressure changes. Autoregulation produces a change in vascular resistance in response to changes in arterial pressure, so as to maintain a constant level of blood flow, especially through the capillaries