Influence of space flight on red blood cells.

Losses of red blood cell mass (RCM) averaging 10-15% have been observed consistently in astronauts after space flight; postflight recovery of RCM requires 4-6 wk. Although apparently not harmful to the health and effectiveness of crews during uncomplicated flights, decreased RCM could compromise health and performance in the event of illness, injury, or partial malfunction of the life support system. Whether the loss of RCM would worsen or stabilize in missions longer than 7 months is unknown. As a biological response, it is a significant, predictable reaction whose etiology, biological mechanisms, and potential operational significance are inadequately defined. Weightlessness is probably the primary cause; however, contributory factors may include hypokinesia/hypodynamia, bone loss, muscle atrophy, altered hemodynamics, stress, and metabolic disturbances. Space medical specialists consider other possible influences such as hypoxia, hypobaria, radiation, toxic contaminants, and launch and reentry accelerations as less likely factors. Because the data base on loss of RCM is insufficient for the National Aeronautics and Space Administration's space medical responsibilities, the Life Sciences Research Office ad hoc Working Group on Space Anemia suggested research approaches ranging form fundamental topics such as utilization of erythropoietin and oxygen in target organs and cell-cell interactions, through possible splenic and vascular dysfunctions, metabolic disturbances, and inhibitors of erythropoiesis, to methodology and models.