A review of hematology studies associated with space flight 1

Abstract

The most significant effect of the space flight environment relative to the blood and blood-forming tissues in man has been a consistent reduction in the circulating red blood cell mass during the flight interval. This finding was first reported during the Gemini IV, V and VII missions, and has since been a consistent observation in the Apollo, Skylab and Apollo-Soyuz flights. Similar results have been reported by Russian scientists following their Salyut missions.

It was initially proposed that the high concentration (near 100%) of oxygen in the spacecraft atmosphere was the cause of the red cell mass loss. This hypothesis was strengthened by similar observations in a chamber study utilizing a 100 percent oxygen atmosphere at a total pressure of 5 psia (identical to that of Gemini and the later portion of the Apollo flights). Studies also revealed subtle alterations in red cell membrane integrity (decreased osmotic fragility, suppression of active potassium transport, increased plasma tocopheral, decreased membrane lipid content) consistent with the concept of a mild oxygen toxicity resulting in intravascular hemolysis.

Data from the Skylab flights are not consistent with the concept of an oxygen-induced intravascular hemolysis. It would appear that some other factor characteristic of the space flight environment (weightlessness?) causes a suppression of red cell production that is not immediately relieved with a return to a normal 1-g environment, except, on longer flights, such as the 84-day Skylab 4 mission, when the red cell mass appears to begin to recover before re-entry. The variations in the magnitude of the loss in individual crewmen and the complicated postflight recovery kinetics suggest a complex relationship between the red cell mass loss and the duration of the exposure to weightlessness. This “anemia of space flight” was frequently accompanied by a reduction in plasma volume, apparently occurring early in the mission and sustained throughout the flight. Other, more subtle, effects have been observed with respect to the function and structure of red blood cells (significant changes in the distribution of red cell shapes during flight and a transient alteration in red cell specific gravity profiles postflight).

The major emphasis of this review will be to address questions relative to the regulation of blood volume during space flight and the causes of its apparent failure.