Dataset for: Hemolysis during and after 21 days of head down tilt bedrest.

Hemoconcentration is observed in bedrest studies, descent from altitude and exposure to microgravity. Hemoconcentration triggers erythrocyte losses to subsequently normalize erythrocyte concentration. The mechanisms of erythrocyte loss may involve enhanced hemolysis, but has never been measured directly in bedrest studies. Steady-state hemolysis was evaluated by measuring 2 heme degradation products, endogenous carbon monoxide concentration [CO] and urobilinogen in feces, in 10 healthy men, before, during and after two campaigns of 21 days of 6° head-down-tilt (HDT) bedrest. The subjects were hemoconcentrated at 10 and 21 days of bedrest: mean concentrations of hemoglobin (15.0±0.2g/L and 14.6±0.1g/L respectively) and erythrocytes (5.18±0.06E6/µL and 5.02±0.06E6/µL respectively) were increased compared to baseline; all p<0.05. In contrast, mean hemoglobin mass (743±19g) and number of erythrocytes (2.56±0.07E13) were decreased at 21 days of bedrest; both p0.05. Indicators of hemolysis mean [CO] (1660±49ppb and 1624±48ppb respectively) and fecal urobilinogen concentration (180±23mg/day and 199±22mg/day) were unchanged at 10 and 21 days of bedrest compared to baseline; both p>0.05. A significant decrease in [CO] (-505ppb) was measured at day 28 after bedrest. HDT bedrest caused hemoconcentration in parallel with lower hemoglobin mass. Circulating indicators of hemolysis remained unchanged throughout bedrest supporting that enhanced hemolysis did not contribute significantly to erythrocyte loss during the hemoconcentration of bedrest. At day 28 after bedrest, decreased hemolysis accompanied the recovery of erythrocytes, a novel finding.