Saunders David K, Roberts Adam C, Aldrich Kevin J, Cuthbertson Brian
Department of Biological Sciences, Emporia State University, KS 66801, USA.
Aviat Space Environ Med. 2002 Jul;73(7):647-53.
Fluid shifts during exposure to microgravity result in a decrease in plasma volume which can lead to a transient increase in hematocrit. This transient increase in hematocrit could result in an increased blood viscosity. Yet, hematocrit returns to near normal values within a matter of hours of microgravity exposure as a result of a reduction in red blood cell mass. Rat tail-suspension models mimic the fluid shifts and hematological changes associated with microgravity exposure.
Tail-suspended rats were monitored for hematological and hemorheological changes over 4, 24, 72, and 168 h of tail suspension. Additionally, hematological and hemorheological changes were followed during recovery periods of 48, 120, and 192 h following 168 h of tail suspension.
Although hematocrit increased significantly by 4 h of suspension, blood viscosity did not differ from controls. However, blood viscosity was significantly greater in the 72-, 168-, and 168/48-h suspension groups relative to controls despite no significant differences in hematocrits between groups. Theoretical calculations of blood viscosity at hematocrits of 50 and 60% (values intended to mimic hematocrits that would occur if red blood cell mass did not decrease) show a significant increase relative to the blood viscosities determined for the actual hematocrits in the experimental groups.
The lowering of hematocrit associated with spaceflight may substantially reduce blood viscosity and thereby maintain the hematocrit at an optimal level for oxygen delivery to tissues.
暴露于微重力环境期间的体液转移会导致血浆量减少，进而可能导致血细胞比容短暂升高。血细胞比容的这种短暂升高可能会导致血液粘度增加。然而，由于红细胞量减少，血细胞比容在暴露于微重力环境后的数小时内会恢复到接近正常的值。大鼠尾部悬吊模型可模拟与微重力暴露相关的体液转移和血液学变化。
对尾部悬吊的大鼠在尾部悬吊4、24、72和168小时期间进行血液学和血液流变学变化监测。此外，在尾部悬吊168小时后的48、120和192小时恢复期内跟踪血液学和血液流变学变化。
尽管悬吊4小时后血细胞比容显著升高，但血液粘度与对照组无差异。然而，72小时、168小时和168/48小时悬吊组的血液粘度相对于对照组显著更高，尽管各组间血细胞比容无显著差异。对血细胞比容为50%和60%（旨在模拟如果红细胞量不减少时会出现的血细胞比容值）时的血液粘度进行理论计算，结果显示相对于实验组实际血细胞比容所测定的血液粘度有显著增加。
与太空飞行相关的血细胞比容降低可能会显著降低血液粘度，从而将血细胞比容维持在向组织输送氧气的最佳水平。
