Publication Abstracts

The hematological responses of rates exposed to conditions of simulated microgravity and acute exercise

Tipton CM, Monnin KA, Hall MC, Sebastian LA
Aviat Space Environ Med 1998: 69:267-76

Abstract

Background: Although humans have experienced microgravity since 1961, it is unknown whether PaO₂ or PaCO PaO₂ will change in humans or in animals exposed to similar conditions. Reports from subjects participating in long-term head down tilt studies indicate that PaO PaO₂ will decrease and PaCO PaO₂ will increase, presumably because of impairments in oxygen delivery and carbon dioxide transport. To investigate this topic with suspended (HDS) rats, we hypothesized that 14 d of HDS would lower resting PaO PaO₂ and elevate PaCO PaO₂ pressures when compared with control rats. Since returning astronauts, previously bed rested subjects, and suspended rats had exhibited decreases in maximum aerobic capacity, we predicted after 2 weeks of HDS, rats performing maximum exercise would demonstrate significant decreases in PaO PaO₂ and elevations in hydrogen ions. Results: Blood gas results during HDS indicated PaO PaO₂ and PaCO PaO₂ partial pressures were significantly decreased during the first week of suspension. Maximal exercise significantly increased PaO PaO₂ in both animal groups, but during exercise the suspended rats exhibited significant increases in lactic acid and hydrogen ion concentrations when compared with control animals. Conclusions: The suspended rat model effectively characterized PaO PaO₂ changes that have been reported for humans exposed to conditions of simulated microgravity. However, the decreases in VO PaO_2max reported for exercising humans and animals could not be explained by PaO PaO₂ changes and the rat model was not effective in predicting changes in blood PaCO PaO₂ Recommendations: NASA should encourage and support studies that characterize PaO PaO₂ and PaCO PaO₂ change in humans and animals, in space and after they return to a 1-G environment.

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Table of Contents for Volume 69, Number 3 of the ASEM journal.