The myogenic response in the microcirculation and its interaction with other control systems.

Evidence for the myogenic response has been obtained from a variety of microcirculatory preparations. In some instances the experimental protocol has involved elevation of arterial pressure or venous pressure alone while in other instances both pressure were elevated. These studies have shown that increased intravascular pressure causes constriction of the arterioles in many but not all vascular beds. This constriction often occurs despite a concomitant reduction in blood flow and tissue oxygen tension. It appears from these studies that individual arterioles are capable of responding to pressure changes. It is also quite likely that the individual responses are modified by conducted responses from neighbouring arterioles. The mechanism of the myogenic response is still a matter of speculation but most observations are consistent with the hypothesis that wall tension is the controlled variable. The series-coupled organization of the arterioles provides a means for modulating the response of the network as a whole since constriction of proximal arterioles to arterial pressure elevation will reduce the increase in pressure that is transmitted downstream to the more distal vessels. This provides a means of autoregulating blood flow during alterations in arterial pressure. There is evidence from microcirculatory studies that the myogenic response tends to maintain a constant capillary pressure.