ACCELERATION-INDUCED EFFECTS ON BABOON BLOOD-CHEMISTRY

Gravity-induced loss of consciousness (G-LOC) is known to have occurre d in pilots since the early 1920's. Most of the research in this area has shown that G-LOC occurs due to a decrease in cerebral blood pressu re and a concomitant reduction in brain perfusion. Since a reduction i n cerebral blood flow can cause transient hypoxia, it is important to study the cerebral metabolism during high +Gz exposure. One component of these studies should include measurements of substrate availability and degradative products. In the present study, adult baboons were gi ven multiple high +Gz exposures (2 to 6) using the Armstrong Laborator y human centrifuge. Venous blood was collected by an automatic syringe withdrawal pump before, during and after centrifuge exposures. The co ncentration of blood gases, glucose and lactate tended to decrease dur ing the centrifuge exposure followed by an increase after the run. Tot al creatine kinase activity in serum was not significantly altered. Th ese results suggest that during +Gz exposure, anaerobic glycolysis is stimulated resulting in elevated lactate production due to a reduction in cerebral blood flow (CBF). The elevated tissue lactate is released into the central circulation upon resumption of normal CBF (after the termination of centrifuge run). Therefore, the observed decrease in l actate concentration during the run may result from a lag in the relea se of tissue lactate into the blood due to a reduction in CBF. It is s peculated that at high +6 Gz, G-LOC may occur as a protective response to reduce the brain metabolic rate, to maintain energy levels and to prevent severe cellular acidosis. However, further research is needed to establish the relationship between the brain's energy status and th e onset of G-LOC.