A Theoretical Method for Estimating Small Vessel Distensibility in Humans

A simple theoretical approach is presented for estimating vascular distensibility of small blood vessels from noninvasively obtained pressure-flow data in the hand and forearm of human subjects. To the extent that Poiseuilleʼs law applies to blood flow in these vascular beds, conductance (the reciprocal of vascular resistance) can be calculated from these data as the ratio of blood flow to mean arterial pressure. The fourth root of the conductance is proportional to the radius of the vascular bed. The slope of the relation between the logarithm of the radius of the vascular bed and the transmural pressure is proportional to the vascular extensibility (E), which, in turn, for small deformations and constant vascular length, is proportional to the distensibility of small blood vessel. Data obtained from the hands of six hypertensive subjects were compared with that obtained from six normotensive subjects, all with their vascular beds in a maximally dilated state. Also compared were data obtained from four normal subjects with their vascular beds in the resting state and when the beds were maximally dilated. The results indicate that 1) in the hypertensive subjects, the small blood vessels of the maximally dilated vascular bed of the hand are significantly (p < 0.02) less distensible (E = 0.126 ± 0.034/mm Hg) than those in the normotensive subjects (E = 0.272 ± 0.047/mm Hg) and 2) the small blood vessels of the normal forearm at resting levels of vasomotor tone are more distensible (E = 1.00±0.38/mm Hg) than in the maximally dilated state (E = 0.51 ± 0.08/mm Hg).