A consistent deficit in the red cell mass has been observed during both the American and Soviet orbital space flights and is sometimes referred to as "astronaut anemia." This may be associated with a reduction in plasma volume so that the hematocrit and the hemoglobin concentration remain unchanged. During the Gemini program, the hypobaric hyperoxic atmosphere of the spacecraft led to oxidative injury to the red cells, causing hemolysis. Thus, the atmosphere proved to be, in part, responsible for the deficit. However, a similar deficit of a lesser magnitude was again observed in subsequent flights with normal ambient PO2 as well as in the Soviet flights in which an atmosphere essentially of see level air is used. The cause of this deficit seems to be suppression of erythropoiesis, as indicated by reticulocytopenia and erythroid hypoplasia of the marrow. No suppression of erythropoiesis has been observed in ground-based experiments carried out under almost identical conditions. Thus, the suppression of erythropoiesis is thought to be related to weightlessness. The reason for the suppression is not known but may be related to total inhibition of bone formation.
在美国和苏联的轨道太空飞行期间，均观察到红细胞量持续不足，有时被称为“宇航员贫血”。这可能与血浆量减少有关，从而使血细胞比容和血红蛋白浓度保持不变。在双子星计划期间，航天器的低压高氧环境导致红细胞受到氧化损伤，引发溶血。因此，事实证明这种环境在一定程度上是造成红细胞量不足的原因。然而，在随后环境氧分压正常的飞行中以及在使用基本为海平面空气的环境的苏联飞行中，再次观察到程度较轻的类似红细胞量不足情况。这种不足的原因似乎是红细胞生成受到抑制，这表现为网织红细胞减少和骨髓红系发育不全。在几乎相同条件下进行的地面实验中未观察到红细胞生成受到抑制。因此，红细胞生成受到抑制被认为与失重有关。抑制的原因尚不清楚，但可能与骨形成的完全抑制有关。
