Effects of hemorrhage on regional cerebral blood flow in awake and in isoflurane-anesthetized rats

: During hemorrhage, redistribution of cerebral blood flow may occur. We compared the effects of hemorrhage on regional cerebral blood flow in awake rats and in rats anesthetized with 1% or 2% isoflurane. In half of each group, regional cerebral blood flow was measured without hemorrhage. The other half was slowly bled to a mean arterial blood pressure of 40-45 mm Hg before measuring the regional cerebral blood flow. Without hemorrhage, the cortical regional blood flow was greater in the awake animals than that of the caudal part of the brain. In the 2% isoflurane group, however, the regional cerebral blood flow of the caudal part was greater than the cortical regional cerebral blood flow. After hemorrhage, a similar decrease (-45%) of the regional cerebral blood flow was observed in each brain region and the pattern of distribution of it remained unchanged in all experimental groups. However, the absolute value of the cortical flow was higher in the awake animals than in the isoflurane groups. Our experiment demonstrated that hemorrhage decreased the regional cerebral blood flow. However, it did not alter the redistribution of the cerebral blood flow in awake animals nor in the animals anesthetized with isoflurane.