CEREBRAL OXYGENATION AND THE RECOVERABLE BRAIN

Oxygenation is the most critical function of blood now and a sudden re duction in oxygen availability is an inevitable consequence of severe ischemia. The resulting cascade of events may result in the failure of membrane integrity of some cells and necrosis, but in the surrounding zone of tissue, less affected by hypoxia, cells survive to form the i schemic penumbra. The timing of these events is uncertain, but suffici ent oxygen is available to these cells to maintain membrane ion pump m echanisms, but not enough for them to generate action potentials and t herefore function as neurons. The existence of such areas has been sus pected for some time based upon the nature of clinical recovery, but h as now been demonstrated by SPECT imaging with a high plasma oxygen co ncentration under hyperbaric conditions as a tracer. A course of hyper baric oxygen therapy frequently results in a permanent improvement in both flow and metabolism. These changes apparently represent a reversa l of the changes that render neurones dormant and the activity of cell s, previously undetectable by standard electrophysiological methods, c an now be demonstrated. Three patients are presented in whom recoverab le brain tissue has been identified using SPECT imaging and increased cerebral oxygenation under hyperbaric conditions. Improved perfusion f rom reoxygenation has correlated with clinical evidence of benefit esp ecially with continued therapy.