Estimations of changes in plasma volume during simulated weightlessness.
Results of previous investigations on the effects of simulated microgravity (thermoneutral (34.5 degrees C) head-out water immersion, WI) have indicated that plasma volume (PV) increases initially and thereafter decreases to attain values below the pre-immersion level.  In these cases, changes in hematocrit (Hct) and hemoglobin concentration (Hgb) were used as indicators of relative changes in PV.  In order to test whether changes in Hct and Hgb are accurate measures of changes in PV during simulated microgravity, direct measurements of PV were performed with a modified Evans blue dye dilution technique before, during, and after a 12 h WI experiment.  Furthermore, PV was determined with the same technique before, during, and after acute 6 degrees head-down tilt (HDT).  Changes in PV were then compared with changes calculated from changes in Hct and Hgb.
Johansen
L B
LB
Danish Aerospace Medical Centre of Research, Copenhagen, Denmark.
Norsk
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D004395:Dye Dilution Technique; D005070:Evans Blue; D018475:Head-Down Tilt / Q000009:adverse effects*; D006400:Hematocrit; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007101:Immersion / Q000009:adverse effects*; D008297:Male; D010953:Plasma Volume / Q000502:physiology*; D018474:Weightlessness Simulation
D006454:Hemoglobins; D005070:Evans Blue