The role of large arteries in controlling blood flow to the hand during severe local cooling
Cold vasodilatation describes the increase in blood flow that follows initial vaso constriction when an extremity is exposed to an environment colder than 12'C. It appears to be due mainly to cold paralysis of local resistance vessels. The reaction is very variable between individuals who are generally chilled; this study was designed to show whether constriction of large arteries of the forearm, protected by fat from local cooling, is responsible for this, enabling such people to maintain low flow and heat loss during cold stress. Twelve subjects were exposed for 120 minutes to warm (38'C), control (24'C) or cold (I 2'C) moving air. During the last half hour the non-dominant hand was cooled in ice water. Arterial diameter and blood velocity in the brachial and radial arteries were measured by ultrasound, and in 6 experiments pressure in both arteries was measured by indwelling cannulae. The arterial diameters constricted significantly in the cold, but only by 27% compared to warm and 17% compared to control (radial), and by 19% compared to warm and 11 % compared to control (brachial). Calculated pressure drop (mean ± S. E. ) between brachial and radial arteries fell from 3.78 ± 0.23 mm Hg in the warm to 2.02 ± 0.15 mm Hg in the cold. During hand immersion in ice water with increased flow, this pressure difference rose in each of 5 cold subjects but never to more than 4.81 mm. Hg. Indwelling arterial cannulae never showed a difference greater than 7.7 mm Hg between brachial and radial arteries in any subject at any time. The general conclusion is that forearm arteries exerted little control over hand blood flow in these circumstances, and that the ability of some people to maintain low blood flow in very cold extremities is due to the ability of downstream vessels to maintain constriction near O degrees C.