Evaluation of cerebral autoregulation following diffuse brain injury in rats

The normal cerebral circulation has the ability to maintain a stable cerebral blood flow over a wide range of cerebral perfusion pressures and this is known as cerebral autoregulation. This autoregulation may be impaired in the injured brain. Closed head injury was induced in 28 Sprague-Dawley rats weighing 400-450 g. Four groups were studied: control group, head injured rat from meter height using 350 g, 400 g and 450 g respectively. CBF, volume velocity was monitored using laser-Doppler flowmetry together with monitoring of ICP and arterial blood pressure. Correlation to assess the relationship between CBF and CPP was done in each animal every hour. If correlation coefficient was > 0.85 and CPP was within normal range, loss of autoregulation was hypothesized. Chi square test, ANOVA test and unpaired Student's t-test were done and significant level of p < 0.05 was established. Mean CBF in injured rats was significantly lower than controls (p = 0.028) at the fifth hour. CBV was lower in the group of 450 g 1 m impact than in controls at 3 h (p = 0.04). Velocity in the group of all injured rats, was significantly lower than in controls at 3 h (p = 0.032) and at 4 h (p = 0.027). Loss of autoregulation was seen during first four hours after trauma in all groups of rats who sustained injury. Statistical significant difference (p = 0.041) in loss of autoregulation between injured and control animals was seen. No loss of autoregulation was observed in the control group. In conclusion CBF and CPP provide information about loss of autoregulation in diffuse brain injury. Decrease in CBF and increase of ICP is observed as a result of loss of cerebral autoregulation. Knowledge of loss of autoregulation could give important information and help in the management of head injured patients.