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  • Title: Hematological and blood viscosity changes in tail-suspended rats.
    Author: Saunders DK, Roberts AC, Aldrich KJ, Cuthbertson B.
    Journal: Aviat Space Environ Med; 2002 Jul; 73(7):647-53. PubMed ID: 12137100.
    Abstract:
    BACKGROUND: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.
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