Failure of autoregulation after closed head injury: an experimental model

Cats were subjected to a 3.5-atm fluid percussion impact administered to the cerebral cortex. Near-infrared spectrophotometry (NIRS) was used to measure the quantity of oxyhemoglobin and total hemoglobin in the illuminated tissue as well as the cytochrome a, a3 redox state. Corroborative data were obtained by freezing brains with liquid nitrogen and measuring cortical concentrations of ATP, creatine phosphate (CP), and lactate. Immediately postimpact there was a rise in mean arterial pressure with a 38% increase of highly oxygenated blood and a shift toward oxidation in the cytochrome a, a3 redox state. By 4 hours postimpact, cytochrome a, a3 was becoming progressively reduced despite the persistence of hyperemia. This was associated with a significant (p less than 0.01) decrease in ATP and CP concentration. Additional studies in which a 0.5-sec, 100-v electrical seizure was induced before and after fluid percussion demonstrated significant differences in seizure response, indicating a failure of autoregulation.