Effects of intermittent reperfusion on brain pH_i, rCBF, and NADH during rabbit focal cerebral ischemia

Background and Purpose: The use of intermittent reperfusion versus straight occlusion during neurovascular procedures is controversial. This experiment studied the effects of intermittent reperfusion and single occlusion on intracellular brain pH (pH_i), regional cerebral or cortical blood flow, and nicotin-amide adenine dinucleotide (NADH) fluorescence during temporary focal ischemia. Methods: Twenty fasted rabbits under 1.0% halothane anesthesia were divided into four groups: (1) nonischemic controls, (2) 60 minutes of uninterrupted focal ischemia, (3) 2×30-minute periods of focal ischemia separated by a 5-minute reperfusion, and (4) 4×15-minute periods of focal ischemia separated by three 5-minute reperfusion periods. Focal ischemia was produced by occlusion of both the middle cerebral and ipsilateral anterior cerebral arteries. After the final occlusion, there was a 3-hour reperfusion period in all groups. Regional cerebral and cortical blood flow, brain pH_i, and NADH fluorescence were measured with in vivo panoramic fluorescence imaging. Results: During occlusion, regional cerebral and cortical blood flows and NADH fluorescence values were not different among the groups. Brain pH_i was significantly lower in the 4×15-minute group compared with the 1×60-minute group (6.57 ± 0.02 versus 6.73 ± 0.06; P<.03) but not significant when compared with the 2×30-minute group. During the short reperfusion periods, all parameters returned to normal except for NADH fluorescence levels, which remained elevated. During the postischemic final reperfusion period, there was a mild brain alkalosis of approximately 7.1 in all groups. There were no significant differences in NADH fluorescence among groups during the final reperfusion. Regional cerebral and cortical blood flow returned to near normal values in all groups. Conclusions: This study demonstrates that intermittent reperfusion during temporary focal ischemia has different effects on the intracytoplasmic and the intramitochondrial compartments: worsening of brain cytoplasmic pH_i but no significant differences in the oxidation/reduction level of mitochondrial NADH.