Changes in lCBF, morphology and related parameters by fluid percussion injury

We investigated the pathophysiological and morphological responses of anaesthetized rats to fluid percussion brain injury generated by an original midline fluid percussion injury device. Following different grades of trauma, lCBF was measured continuously in the right parietal cortex through a burr hole using laser Doppler flowmeter, and physiological parameters were monitored. Pathological changes also were evaluated microscopically. During the first 2 hours following trauma, we found four patterns of cerebral circulatory responses. Little measurable pathophysiological response occurred after percussion pulses of less than 1.33 atmospheres (atm). In animals subjected to pulses of greater than 4.30 atm, lCBF increased synchronously with blood pressure, and then both parameters decreased continuously until death. In animals subjected to pulses of 1.53 to 2.33 atm, trauma produced a transient increase in lCBF with no synchronous rise in blood pressure. In animals subjected to pulses of 2.70 to 3.87 atm, lCBF increased synchronously with blood pressure immediately following the injury, but had decreased markedly by 60 seconds and remained below the pre-injury baseline. Blood pressure recovered to baseline within 4 minutes of the injury. The transient increase in lCBF occurred within 5 seconds following percussion pulses of greater than 1.53 atm and appeared to be independent of the rise in systemic blood pressure. Apnoea occurred in animals subjected to pulses of greater than 1.53 atm, and the duration of apnoea and mortality rate correlated with the magnitude of the applied injury. A power decrease in the electroencephalogram post-injury and a delay in its recovery, both depended on the magnitude of the injury with few regional differences in the beta-2 band power. The distribution and extent of blood-brain barrier disruption and small haemorrhages also correlated with the magnitude of the injury. The number of neurons decreased significantly in both hippocampi by 2 weeks following moderate trauma. The four patterns of lCBF changes demonstrated in the present study, as well as the other responses to injury, may be useful for studying graded models of various diffuse brain injuries.