Comparison of peripheral vascular resistance based on macro- and micro-circulatory responses by Poilleuille’s law

The total peripheral vascular resistance (TPR) is essential index in the cardiovascular system, since both the systemic blood pressure and blood flow could be determined by the changes of TPR. Such important index, the TPR cannot be measured directly, so Darcy’s law would be applied to determine TPR. On the other hand, vascular flow resistance would be mainly controlled by the contraction or dilation of small arteries and arterioles, existing at the upstream of capillaries. Regarding the single small artery and the arteriole, the vascular flow resistance (R) could be represented as R=8µL/πr4, called Poilleuille’s law (µ: viscosity, r: vessel radius L: vessel length=constant). In addition, the major contribution of these vascular resistances would be caused by the resistance vessels in the skeletal muscle, since the blood flow in skeletal muscle dramatically changes from resting to excise, approximately 20 times increases. These facts suggest the TPR would be determined by the levels of contraction and dilation in skeletal muscle arterioles. In the present study, we tried to investigate in macro- and microcirculation whether the TPR can be estimated from the diameter changes of single arteriole in the skeletal muscle using Dalcy and Poilleuille’s laws. Wister rats (180 - 400g b.w.) were anesthetized, and carotid artery and vein were canulated for the blood pressure measurement and administration of L-NAME, inhibiter of NOS production, respectively. The observation of microcirculation was carried out in the cremaster muscle by intravitalmicroscopy. The TPR was calculated by the changes in the blood pressure during L-NAME caused vasoconstriction based on the Dalcy’s law, while the R was calculated by the changes in the arteriolar diameter based on the Poillleulle’s law. The TPR and R were increased 23.9±7.7% and 23.5±8.7% from control to L-NAME caused vasocontraction, respectively. These results suggest the Poilleulle’s law can apply to estimate the TPR in vivo microcirculation. Furthermore, it has been confirmed the TPR would be regulated mainly by the contraction and dilation of the skeletal muscle arterioles.