Vascular resistance of arterioles with nonuniform diameters.

Arterioles in various vascular beds have been often observed to have nonuniform diameters along the vessel axis. The effect of nonuniformity of arteriolar diameter on vascular resistance was investigated using a theoretical model of blood flow in arterioles. Viscous flow of a Newtonian fluid in tubes with periodically changing diameters along the tube axis was analyzed by a finite element method based on the Stokes equations. Vascular resistance for the nonuniform tube was computed over a spatial period of the variation in diameter and was compared to resistance for a uniform tube with a constant diameter equal to the mean diameter of the nonuniform tube. In all cases, resistance for a tube with a nonuniform diameter was larger than resistance for a uniform tube with a diameter equal to the mean diameter of the nonuniform tube. Increases in the amplitude of the variation in diameter resulted in a rapid increase in resistance when the period of the variation remained constant. On the other hand, as the period of the diameter variation increased when amplitude remained constant, resistance decreased and approached the values obtained under the assumption of a Poiseuille flow at each cross section of the tube in the limit of an infinite period. Our theoretical model was applied to our previous in vivo studies of vessel diameter nonuniformity for rabbit mesentery arterioles in a contracted state. It was shown that vascular resistance calculated by our model was 2 to 11% higher than resistance obtained for a uniform tube with a diameter equal to the mean diameter of the arteriole.