PULMONARY TISSUE VOLUME, CARDIAC-OUTPUT, AND DIFFUSING-CAPACITY IN SUSTAINED MICROGRAVITY

In microgravity (mu G) humans have marked changes in body fluids, with a combination of an overall fluid loss and a redistribution of fluids in the cranial direction. We investigated whether interstitial pulmon ary edema develops as a result of a headward fluid shift or whether pu lmonary tissue fluid volume is reduced as a result of the overall loss of body fluid. We measured pulmonary tissue volume (Vti), capillary b lood flow and diffusing capacity in four subjects before, during, and after 10 days of exposure to mu G during space-flight. Measurements we re made by rebreathing a gas mixture containing small amounts of acety lene, carbon monoxide, and argon. Measurements made early in flight in two subjects showed no change in Vti despite large increases in strok e volume (40%) and diffusing capacity (13%) consistent with increased pulmonary capillary blood volume. Late inflight measurements in four s ubjects showed a 25% reduction in Vti compared with preflight controls (P < 0.001). There was a concomittant reduction in stroke volume, to the extent that it was no longer significantly different from prefligh t control. Diffusing capacity remained elevated (11%; P < 0.05) late i n flight. findings suggest that, despite increased pulmonary perfusion and pulmonary capillary blood volume, interstitial pulmonary edema do es not result from exposure to mu G.