The role of flow bifurcation in creating an oscillatory flow in capillary blood vessels

Abstract

The blood flow in some capillary blood vessels is not steady, but experiences an intermittent fluctuation. As a mechanism responsible for such a fluctuation, the action of the precapillary sphincter muscle was mentioned in addition to the pulsatile pressure in arteries and veins. The velocity of the blood in capillary blood vessels depends on the imposed pressure gradient and the resistance of the blood vessel to the blood flow. Since the pulsation of the blood pressure in arteries and veins can change the pressure gradient in capillary blood vessels, and the action of precapillary sphincter muscle changes the resistance of the capillary blood vessels, such mechanisms are undoubtedly responsible for some fluctuations in the capillary blood flow. It is well known that the velocity of the blood in the capillary blood vessels depends also on the apparent viscosity of the blood, which is a function of the number density of red blood cells in the capillary blood vessels. Hence, the change of the number of red blood cells in time in a certain length of a capillary blood vessel can result in an intermittent fluctuation in the blood velocity. If red blood cells are not uniformly distributed in the upstream blood vessel, the red blood cell flux entering the capillary blood vessel branching from such a blood vessel can vary in time. This variation of red blood cell flux can cause an intermittent fluctuation in the number of red blood cells in the branching capillary blood vessel. In this study, the red blood cell partition in a bifurcating blood flow is studied as a mechanism responsible for some fluctuations in the motion of the blood in capillary blood vessels. The results of this analysis show that a non-uniform distribution of red blood cells in the upstream blood vessel can create an intermittent fluctuation in the blood velocity in the branching capillary blood vessel, provided the traverse time for the blood to flow the entire length of the capillary blood vessel is properly matched to the period of oscillation in the local capillary hematocrit.