Publication Abstracts

Brief Exposure to -Gz Reduces Cerebral Perfusion Pressure during Subsequent +Gz Stress in Rats

Don D. Sheriff, Ph.D., Wayne M. Isdahl, M.S., Christopher D. Nelson, B.S., and Paul M. Werchan, Ph.D.
Aviat Space Environ Med 2001; 72:8-12

Abstract

Introduction: In humans, +Gz exposure immediately preceded by exposure to zero or -Gz can result in unexpected incapacitation ("push-pull" effect). Our goals were to establish whether this phenomenon exists in rats and to evaluate the importance of varying the duration of -Gz exposure on magnitude of the push-pull effect on cerebral perfusion pressure. Methods: Eight conscious male rats were studied in the transition from + 5 Gz to +10 Gz imposed by centrifugation. This was done with (push-pull) or without (control) 2 s exposure to -5 Gz applied using a counterbalanced design. Seven isoflurane anesthetized rats were studied in the transition from 0Gz (+1Gy) to + 1Gz imposed by tilting. This was done with (push-pull) or without (control) 0.5, 1, 3, or 9 s exposure to -1Gz imposed immediately prior to the transition applied using a counterbalanced designed. Results: Exposure to 2 s of -5 Gz significantly (p < 0.01) reduced carotid artery pressure in the 4^th through 8^th s of exposure to +10 Gz by an average of 15 mmHg compared with control. In the tilt experiments, a push-pull effect was found with mild Gz exposure (±1Gz) with as little as 0.5 s -Gz exposure. Varying the head-down dwell time did not alter the magnitude of the exaggerated hypotension induced by "push-pull" (p = 0.90). Conclusions: We conclude that rats express a "push-pull" effect similar to that observed in humans but that altering the duration of exposure to -Gz does not influence the magnitude of the "push-pull" effect.

Keywords: push-pull, acceleration, G-LOC, G-tolerance, microgravity, BP, tilting.

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Table of Contents for Volume 72, Number 1 of the ASME journal.