Changes in blood flow in a conduit artery and superficial vein of the upper arm during passive heating in humans

The purposes of this study were (1) to evaluate changes in blood flow in the brachial artery and basilic vein of the upper arm with a rise in internal temperature during passive heating; and (2) to investigate the contributions of blood velocity and anteroposterior vessel diameter to these blood flow changes. Ten subjects rested in the supine position between a pair of tube-lined sheets. Thermoneutral water was circulated through the tubes to keep a mean skin temperature of 34–35°C, and then hot water was circulated to maintain of 37–38°C. The blood velocity and diameter in the brachial artery and basilic vein were continuously monitored by Doppler ultrasound technique and used to calculate blood flow. Blood flow in the brachial artery and basilic vein increased linearly as the oral temperature (T _or) rose by ≤0.6°C. The magnitude of the change in blood flow did not differ significantly between the two vessels. In addition, plots of ΔT _or versus blood flow yielded slopes that did not differ significantly between the brachial artery and the basilic vein. As T _or increased, blood velocity, but not diameter, also increased. In conclusion, blood flow in the brachial artery and the basilic vein increased linearly as the internal temperature variable T _or increased ≤0.6°C. In both vessels, the passive heating-induced increases in blood flow resulted primarily from a change in blood velocity, rather than from a change in diameter.