Flow thresholds of functional and morphological damage of brain tissue

Abstract

Flow thresholds of functional and morphological damage in animal studies are discussed. After focal ischemic attacks symptoms may recover completely or partially either shortly after the occurrence of the deficits or more rarely with long intervals after the onset, and such improvements may occur spontaneously, or after surgical revascularization, perfused at a value insufficient for functional activity but adequate for structural integrity. Slight flow increase restore function in viable cells. The concept of the ischemic penumbra is complicated by two facts: the duration of ischemia on cell damage, which itself is dependent on the absolute value of residual flow; and the high variability of ischemic vulnerability among different neurons. It has to be kept in mind that the destruction of the most sensible neurons is important for the irreversibility of the neurological defect. Therefore, the ischemic cell damage of the most vulnerable part must be prevented. In principle, this can be done by improving the flow to the critical area by a small amount (0.1-0.2 ml/g/min) within the tolerable time limits. As long as clinical neurology is still far from being able to fulfill this requirement, helpful therapeutic regimens could be initiated by studies of regional cerebral blood flow and metabolism in stroke victims to select cases with still viable but functionally inactive tissue.