Changes in brain stem blood flow under various grades of brain stem ischemia

This report describes a study of brain stem blood flow (BBF) change under various grades of brain stem ischemia in a new experimental rat model. The main damage was caused by occlusion of the median and paramedian perforating arteries of the basilar artery. In this model, hyperperfusion was generally observed in cases of mild or moderate ischemia within 1 hr after recirculation and lasted for approximately 1 hr. During hyperperfusion, BBF increased to over 60 ml/100 g brain/min and was significantly greater than basal values (p less than 0.01). The fact that hyperperfusion was unobserved in some cases might be due to the degree of damage to the medulla oblongata. Hypoperfusion or lack of reflow phenomena was also followed by severe ischemia with remarkable hypotension. It is fairly clear from our results that the pattern of postischemic hyperperfusion is responsible for decreased oxygen availability in the brain stem and dysfunction of autoregulation. Acetazolamide reactivity was disturbed and had an inverse response during hyperperfusion. Such phenomena can be explained by paralytically dilated vessels due to ischemia. If BBF falls below a critical level, as we have seen, postischemic hyperperfusion may be induced with dysfunction of autoregulation and inverse acetazolamide reactivity due to vasoparalysis in the brain stem.