Regulation of the lumen of a resistance blood vessel by mechanical stimuli

The flow in a vessel able to regulate its lumen under the action of mechanical stimuli, the variation of the pressure difference between the inner and outer surfaces of the vessel wall and the blood flow velocity, is described. This ability is determined by the effect of the mechanical stimuli on the degree of activation of smooth muscle cells in the vessel wall. In order to describe the active properties of the wall, two controlling parameters which have the sense of the concentration of free calcium ions in the cytoplasm of smooth muscle cells and the average concentration of nitric oxide in the smooth muscle layer, are introduced. The approach proposed makes it possible to estimate both the degree of participation of each mechanical stimulus in vessel lumen regulation and the result of interaction of two differently directed vascular responses. The calculations show that both the magnitude and direction of the radius response to a mechanical stimulus depend on the initial state of the vessel wall. The role of the vessel wall sensitivity to mechanical stimuli in the stabilization of the blood flow-rate and the variation of the radius along the vessel is considered.