Skin vascular bed is a potential blood reservoir during heat stress

To determine the potential role of the skin vasculature as a blood reservoir, we measured venous compliance (Cv), resistance (Rv), and their product, the time constant of venous drainage (tau sk = RvCv), in skin flaps from the hindlimbs of 15 dogs anesthetized with pentobarbital sodium at different core temperatures (Tc, 37-42 degrees C), skin temperature (Ts, 25.3-50.0 degrees C), and during an infusion of papaverine (5%). The vasculature of the flap was isolated, and a double-occlusion technique was used to measure the static pressure in the venous compartment. The blood volume of the flap was altered by changing either flow or outflow pressure (Pv). The change in volume was estimated from the change in weight of the flap with a force transducer. At Tc = 37 degrees C, Rv was 2.27 +/- 0.81 mmHg.min.ml-1.100 g-1 (means +/- SD), Cv was 0.17 +/- 0.06 ml.mmHg-1.100 g-1, and tau sk was 28.0 +/- 8.8 s. Rv decreased with elevated Tc, Ts, and with papaverine. Cv increased with a rise in Tc and Ts. Increasing Tc and Ts did not change tau sk, but the papaverine infusion shortened it. The lowest tau sk (20 s) occurred during maximal vasodilatation. This long tau sk indicates that the skin could serve as a blood reservoir during heat stress.