Small vessel responses of the dog paw

Abstract

Pressures and flows were measured in small veins and arteries of the dog hind paw during stimulation of the ipsilateral lumbar sympathetic trunk. At stimulation frequencies less than 1–2/sec. the constrictor response was limited to very small arteries, or arterioles. Small artery pressure increased while small vein pressure and blood flow decreased. At stimulation rates from 1–2/sec. to 10/sec. small vein pressures were progressively increased while small artery pressures and blood flows were progressively decreased. At higher stimulation frequencies flow stopped, and small artery pressures fell to low levels (in many experiments to values well below the plasma oncotic pressure). Closure of arteries occurred at the ankle and a static column was formed which communicated with the capillaries. Simultaneously small vein pressure rose well above the oncotic level and was long maintained. The small vein walls were contracting against a static column of blood held between a strong constriction (closure?) at the ankle level and postcapillary venular valves (or constrictive closure). Since these high pressures occurred after flow had stopped they could not be relevant to transcapillary water shifts.