Venous return from distal regions affects heat loss from the arms and legs during exercise-induced thermal loads

To study the role of venous return from distal parts of the extremities in influencing heat loss from the more proximal parts, changes in mean skin temperature (Tsk) of the non-exercising extremities were measured by color thermography during leg and arm exercise in eight healthy subjects. Thirty minutes of either leg or arm exercise at an ambient temperature (Ta) of 20 degrees C or 30 degrees C produced a greatly increased blood flow in the hand or foot and a great increase in venous return through the superficial skin veins of the extremities. During the first 10 min of recovery from the exercise, blood flow to and venous return from the hand or foot on the tested side was occluded with a wrist or ankle cuff at a pressure of 33.3 kPa (250 mm Hg), while blood flow to the control hand or foot remained undisturbed. During the 10-min wrist occlusion, Tsk increased significantly from 28.3 degrees +/- 0.41 degrees C to 30.1 degrees +/- 0.29 degrees C in the control forearm, but remained at nearly the same level (28.0 degrees +/- 0.34 degrees C to 28.2 degrees +/- 0.25 degrees C) in the occluded forearm. In the legs, although Tsk on both sides was virtually identical (32.0 degrees +/- 0.31 degrees C, control vs 32.0 degrees +/- 0.36 degrees C, tested) before occlusion, Tsk on the control side (32.6 degrees +/- 0.27 degrees C) was significantly higher than that on the tested side (32.2 degrees +/- 0.21 degrees C) after ankle occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)