On the morning of the test, an intravenous catheter, using a 20 gauge IV intercath, will be placed in an antecubital vein in one arm both for sampling and for infusion. Veins will be kept patent with an infusion of NaCl (0.9%) at 25 mL/hr throughout the test. The arm from which samples are obtained will be warmed to 55 C with a heating blanket to assist in the arterialization of the venous samples.