The pre- to post-capillary resistance ratio in the human forearm.

Abstract

A plethysmograph made of two rubber bladders, enclosed in a sleeve of thin brass sheet, was used to measure capillary filtration rate [Formula: see text] in the forearms of five supine subjects at a room temperature of 27 ± 1 °C, at several plethysmograph pressures (pPL) between 0 and 25 mm Hg while venous pressure (pV) was held constant. We (Newberry et al. 1970) reported previously that in the same five subjects [Formula: see text] increased linearly with pV at a mean rate of 0.00357 ml/min∙100 ml∙mm Hg. [Formula: see text] decreased linearly with pPL in each subject (r varied from −0.81 to −0.99) at a mean rate of −0.00538 ml/min∙100 ml∙mm Hg. Compared as paired values the absolute values of these rates are significantly different (p < 0.02). It is shown that the pre- to post-capillary resistance ratio (rA:rV) can be determined from the relationship between the rates of change of [Formula: see text] with change of pV and pPL. The mean value of this ratio was 2:1 with a range from 1.03:1 to 3.5:1. It is likely that the absolute value of [Formula: see text]/ΔpPL is the capillary filtration coefficient.