Distensibility of Blood Vessels of the Human Calf Determined by Local Application of Subatmospheric Pressures

Abstract

The increases in volume of the human calf were measured on exposure to those subatmospheric pressures which bring about increases in the transmural pressure of the blood vessels of the same order as those normally encountered due to postural change. It was concluded that these volume changes were due to blood. It was found that the volume of extra blood which could be accommodated in the calf at any level of subatmospheric pressure was fairly constant for each subject and varied little between the subjects tested. The pressure-volume curve was not altered by local heating of the calf, or by general heating of the subject to release sympathetic vasomotor tone. The curve was depressed by severe local cooling. In some experiments exercise of the calf muscles was performed for the 2nd minute of a 3-minute period of suction. This exercise made no difference to the amount of extra blood which could be held in the calf during the 3rd minute. During the exercise the volume of extra blood was reduced, owing to the action of the muscle pump. This reduction in volume was independent of the size of the increase in transmural pressure, once a certain level of exercise had been attained. It was concluded that factors which caused an increase in peripheral blood flow have no effect on the over-all capacity of a limb. Local cooling causes reduction in this capacity. Submitted on August 16, 1956