Effect of a surgically created side-to-side arteriovenous fistula on heat elimination from the human hand and forearm: evidence for a critical role of venous resistance in determining fistular flow.

1. In eight patients with a unilateral fistula between the radial artery and a nearby superficial vein, heat elimination from both hand and forearm, as measured by calorimetry, was always substantially greater on the side of the fistula (a mean excess from hand-plus-forearm 889 J/min). 2. Fistular blood flow measured by hand-plus-forearm plethysmography in these patients averaged 431ml/min. Correlation between fistular blood flow and heat elimination was poor (r = 0.70, P less than 0.06), probably because heat elimination due to the fistula takes place mainly from veins, whose pattern varies from patient to patient. 3. Approximately half of the total increased heat elimination due to the fistula is from the hand. Occlusion of the circulation to the hand caused fistular flow rate to be reduced by about half. This suggests that the main resistance to fistular is venous, proximal veins offering a similar resistance to distal veins. 4. The obligatory heat loss due to fistula is unlikely to embarrass temperature regulation, except in severe cold stress.