Continuous monitoring of posttraumatic cerebral blood flow using laser-Doppler flowmetry

Traumatic brain injury causes alterations in cerebral blood flow that are thought to influence secondary pathophysiology and neurologic outcome in humans. Since it is difficult to study early changes in blood flow in head-injured patients, animal models of brain injury must be employed. However, techniques to monitor brain blood flow in animals are labor intensive and generally provide discontinuous flow measurements. The present study examines the application of laser-Doppler flowmetry for measurement of cerebral blood flow following experimental brain injury. This method allows continuous monitoring of local cerebral blood flow before, during, and after injury. Rats (n = 9) were prepared for lateral fluid percussion injury under barbiturate anesthesia. Injury (2.10 +/- 0.02 atm) was induced over the right parietal cortex, and blood flow was monitored in the contralateral cortex. Seconds after the peak hypertension after injury, blood flow in the left parietal cortex increased 226% +/- 18% (means +/- SEM). This increase was transient, with blood flow falling below control values within minutes. Five minutes after injury, blood flow was 83% +/- 8% of control, and at 1 h, this value had fallen to 56% +/- 6%. Blood flow at 60 min was 93% +/- 5% of control in the sham-injured group (n = 10). The reduction in cerebral blood flow in our laser-Doppler study was of similar magnitude as previously reported in rats injured at a similar intensity when blood flow was examined with radiolabeled microspheres. Given these results, we believe laser-Doppler flowmetry can be used to continuously monitor posttraumatic blood flow following experimental brain injury.