Functional aspects of myogenic vascular control.

Recent in vivo observations, especially in skeletal muscle, of macro- and microvascular myogenic reactivity and its functional consequences suggest that myogenic regulatory mechanisms contribute directly or indirectly to circulatory homeostasis by exerting the following main functions: (1) A blood pressure-induced tonic excitatory function of the vasculature, thereby initiating a pronounced intrinsic myogenic basal tone in the arterial microvessels; (2) a homeostatic resistance function (high total peripheral resistance), mainly exerted by the myogenic tone and serving to maintain normal arterial pressure at rest; (3) functions serving to improve nutritional flow and exchange, exemplified by blood flow recruitment, capillary recruitment, adjustments to the capillary perfusion:diffusion ratio for optimum exchange in the heterogeneous capillary network, and reactive hyperaemia; and (4) protective functions directed against harmful circulatory effects of changes in blood pressure, exemplified by autoregulation of blood flow and autoregulation of capillary hydrostatic pressure during changes in arterial pressure, and by autoregulation of transcapillary filtration during a hydrostatic load on the vascular bed.