Hematological and blood viscosity changes in tail-suspended rats.
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.
Saunders
David K
DK
Department of Biological Sciences, Emporia State University, KS 66801, USA. saunderd@emporia.edu
Roberts
Adam C
AC
Aldrich
Kevin J
KJ
Cuthbertson
Brian
B
D000818:Animals; D001809:Blood Viscosity / Q000502:physiology*; D015992:Body Mass Index; D004906:Erythrocyte Count; D004907:Erythrocyte Deformability / Q000502:physiology; D004909:Erythrocyte Indices; D018495:Fluid Shifts / Q000502:physiology*; D006400:Hematocrit; D006454:Hemoglobins / Q000032:analysis; D018056:Hemorheology; D019417:Hindlimb Suspension / Q000502:physiology*; D006706:Homeostasis / Q000502:physiology; D016014:Linear Models; D008297:Male; D023421:Models, Animal; D011237:Predictive Value of Tests; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D006454:Hemoglobins