Objective To investigate the changes of cerebral blood flow and the level of brain injury in a rat model of deep hypothermia low flow(DHLF).Methods Twelve SD rats aged 3 weeks were randomly divided into sham group and model group.Regional cerebral blood flow(rCBF)of all rats was measured continuously during the operation by laser Doppler flowmetry,and the changes of rCBF were measured before temperature decreased,when the temperature decreased to(21.0±0.5)℃,0-5 minutes,25-30 minutes,55-60 minutes,115-120 minutes during DHLF and 0-5 minutes after DHLF operation.Another 60 SD rats aged 3 weeks were randomly divided into sham group and model group.Six rats of each group were sacrificed at 1,6,24,72 hours and 7 days after DHLF operation to detect the pathological changes of the brain and the neuronal apoptosis by HE staining and TUNEL assay.The neurological deficit score(NDS)was recorded at 24,72 hours and 7 days after operation for evaluating the neurologic functional outcome.ResultsWhen the temperature was decreased to(21.0±0.5)℃,the levels of rCBF of sham group and model group were significantly decreased to(41.1±4.2)% and(40.7±3.4)% of the baseline value,and the rCBF level of model group was further decreased to(15.7±3.5)% of the baseline value 0-15 minutes during DHLF(P ＜ 0.01),with no obvious changes in all the time intervals during DHLF.Compared with the sham group,the scores of NDS of model group were significant lower at 24 and 72 hours after operation(P ＜ 0.05 or 0.01).Besides,a significant pathological change of the brain tissue and a increased percentage of TUNEL-positive staining cells were observed in model group at 6,24,72 hours and 7 days after operation(P ＜ 0.01).Conclusions Rat model of DHLF is an ideal and reliable model of brain injury,for it is similar to DHLF procedure of clinical cardiac operation.