Role of response to changes in flow rate in the regulation of vessel radius and blood flow

Estimates are presented for the effect of susceptibility of the inner surface of the blood vessel wall to shear stress on changes in diameter and volume blood flow rate. The model of thin-walled vessel with radius controlled by two parameters is used. The effect of rheological factors, hematocrit, and oxygen content in blood on the value of vessel response to a change in shear stress is considered. The estimates showed that the contribution of the vessel response in question to a change in blood volume flow rate amounts tens per cent. The influence of rheological (Fahraeus and Fahraeus-Lindqvist) effects on flow rate lies within several per cent. The role of the vessel response considered increases with anaemia: at low hematocrit its contribution to increase in flow rate exceeds 10%. Variation of oxygen concentration within the normal range has almost no effect on the hemodynamic parameters. With hypoxia, on the contrary, the participation of this response on changes in flow rate weakens: in severe hypoxia decrease in blood flow rate owing to a change in oxygen concentration equals approximately 9%.