UNLABELLED: A study was made of changes in brainstem blood flow (BBF) under various grades of ischemia in a rat recirculation model. MATERIALS AND METHODS: Adult male Wistar rats were anesthetized with pentobarbital sodium (40mg/kg i.p.). After exposure of the cervical vertebra (C2 portion), embolic threads of various sizes prepared were inserted into the vertebral artery. By the hydrogen clearance technique, changes in BBF were measured in 30 rats before, during and after brainstem ischemia. RESULTS AND DISCUSSION: The mean arterial blood pressure (MABP) was 113 +/- 5.8mmHg, and the mean BBF was 35.5 +/- 2.4ml/100g/min before ischemia. The alteration of BBF during and after ischemia was classified into three groups. The mildly ischemic group showed no significant changes in MABP; BBF was above 15ml/100g/min during ischemia, with slight reactivity revealed by acetazolamide after recirculation. In the moderately ischemic group, MABP dropped significantly to 62.0 +/- 12.4mmHg. After recirculation, it increased gradually to almost the control level. BBF decreased to below 15ml/100g/min immediately after ischemia, followed by a gradual increase to hyperperfusion after recirculation. After 1hr of recirculation, BBF increased to more than 60ml/100g/min with inverse acetazolamide reactivity. In the severely ischemic group, both BBF and MABP decreased irreversibly even after recirculation. These data indicate that the changes in MABP and BBF could be classified according to the degree of ischemic damage in the brainstem, where the vasomotor center is located. Acetazolamide reactivity was disturbed during hyperperfusion. Such phenomena could be explained by the presence of paralytically dilated vessels. If BBF falls below the critical level, as we showed here, it may induce postischemic hyperperfusion associated with dysfunction of autoregulation and vasoparalysis in the brainstem.
UNLABELLED: A study was made of changes in brainstem blood flow (BBF) under various grades of ischemia in a rat recirculation model. MATERIALS AND METHODS: Adult male Wistar rats were anesthetized with pentobarbital sodium (40mg/kg i.p.). After exposure of the cervical vertebra (C2 portion), embolic threads of various sizes prepared were inserted into the vertebral artery. By the hydrogen clearance technique, changes in BBF were measured in 30 rats before, during and after brainstem ischemia. RESULTS AND DISCUSSION: The mean arterial blood pressure (MABP) was 113 +/- 5.8mmHg, and the mean BBF was 35.5 +/- 2.4ml/100g/min before ischemia. The alteration of BBF during and after ischemia was classified into three groups. The mildly ischemic group showed no significant changes in MABP; BBF was above 15ml/100g/min during ischemia, with slight reactivity revealed by acetazolamide after recirculation. In the moderately ischemic group, MABP dropped significantly to 62.0 +/- 12.4mmHg. After recirculation, it increased gradually to almost the control level. BBF decreased to below 15ml/100g/min immediately after ischemia, followed by a gradual increase to hyperperfusion after recirculation. After 1hr of recirculation, BBF increased to more than 60ml/100g/min with inverse acetazolamide reactivity. In the severely ischemic group, both BBF and MABP decreased irreversibly even after recirculation. These data indicate that the changes in MABP and BBF could be classified according to the degree of ischemic damage in the brainstem, where the vasomotor center is located. Acetazolamide reactivity was disturbed during hyperperfusion. Such phenomena could be explained by the presence of paralytically dilated vessels. If BBF falls below the critical level, as we showed here, it may induce postischemic hyperperfusion associated with dysfunction of autoregulation and vasoparalysis in the brainstem.