The cause of acute brain swelling after the closed head injury in rats.

The major component of acute brain swelling was determined using a new closed head injury (CHI) model in rats. Twenty seven Sprague-Dawley rats were separated into four groups (Sham, CHI, CHI combined with hypotension and CHI combined with hypoxia and hypotension). Hypoxia (pO2 of 40 mmHg) and hypotension (mean arterial blood pressure of 30 to 40 mmHg) were induced immediately after head injury and were maintained for 30 minutes. These experiments were terminated at two hours after CHI by transcalvarial freezing with liquid nitrogen. Blood pressure, intracranial pressure (ICP) and physiological parameters were monitored. Regional cerebral blood volume and water content were measured quantitatively. Rats with CHI, and with CHI and hypotension, had mild increase in ICP. Otherwise, rats with CHI, hypoxia and hypotension showed a significant increase in ICP (36.2 +/- 5.6 mmHg). Water content showed an increase of 1.6% in the estimated total brain and 2.4% in the cerebral cortex in those rats. Cerebral blood volume decreased by 61.4% in the total brain and 57.3% in the cortex. There was a reduction in the cerebral hematocrit of 2.4% in the total brain and 4.7% in the cortex. The main component of brain swelling in this head injury model was brain edema. Cerebral blood volume and hematocrit were reduced in the remarkable edematous brain.