Lactic Acid Concentration of Brain Tissues of Dogs Exposed to Hypoxemia and/or Hypocapnia

¹ From the Department of Physiology-Biophysics, School of Aviation Medicine, USAF, Randolph AFB, Texas

Dogs were exposed to hypocapnia, hypoxemia with hypocapnia, and hypoxemia without hypocapnia for 30 minutes, then decapitated. Three hours later brain samples of white matter from the corona radiata and corpus callosum, gray matter from the caudate nucleus and cerebral cortex and a mixture of white and gray matter from an entire cerebral hemisphere, were analyzed for lactic acid. Gray matter contained more lactic acid than white matter and a mixture from the cerebral hemisphere was intermediate in concentration. Hypocapnia did not elevate significantly blood or brain lactic acid above control levels. However, hypoxemia with hypocapnia and hypoxemia without hypocapnia produced a statistically significant elevation of lactic acid. The results in the latter group were different from those obtained previously in dogs exposed for 15 minutes, the difference apparently being due to cardiovascular changes which decreased cerebral blood flow. The results indicate that the lactic acid level of carefully sampled brain tissues may be used to determine whether or not hypoxemia was present at the time of death and to distinguish this condition from hypocapnia.