[Changes in oxygen supply and utilization in head-down tilted humans]

Generalized data on the oxygen transport function of blood in human subjects during head-down tilt (HDT) collected with invasive and non-invasive methods point it that oxygen utilization by the systemic blood circulation does not reflect O2 utilization by the local one. After a week in HDT, local O2 utilization was found increased. A largely normal O2 content and pressure in arterial blood, significant decreases of these parameters in peripheral venous blood, and a concurrent slight growth of lactate are indicative of local circulatory hypoxia in blood flowing out of the arms of HDT subjects. Findings of the microgravity simulation studies bring up the necessity to control local oxygen supply in humans who for some reasons lack standard countermeasures during space flight.