Global brain ischemia is a total cessation or drastic decrease in total brain circulation. There are various ways this disaster may befall you. For example, if you're the King of France and you piss off a bunch of revolutionaries ca. 1789, they might be inclined to introduce you to Dr. Guillotine's favorite invention. This encounter will leave you about a foot shorter and afflicted with permanent global brain ischemia. In the 21st century, however, the most common cause for global brain ischemia is from cardiac arrest. In the vast majority of cases, we don't care, because just like Louis XVII's, this brain ischemia is permanent (the patient is dead--happens to everybody).

But if you come along and resuscitate a  patient from cardiac arrest, then blood flow to the brain is restored, and now you have transient global brain ischemia. The patient is now in the condition known as reperfusion. After global brain ischemia, most brain tissue recovers. Unfortunately some of it doesn't--and it just so happens that the brain tissue that doesn't recover is the brain tissue that you think and remember with. It's a bummer.

Neuronal Death after Global Brain Ischemia.  In the top left image observe a nonischemic (normal) rat hippocampus, and in particular the most dorsal layer, a darkly-staining plate of neurons called CA1. The bottom left image is a higher-power view of this region, revealing plump, juicy, happy CA1 pyramidal neurons. In the top right panel, we see the results of 8 min of global brain ischemia followed by 7 days of reperfusion: the CA1 no longer stains because, as the high-power image at bottom right demonstrate, the CA1 neurons have been destroyed. Note, however, that other regions of the hippocampus continue to stain and are in fact still viable. This is an example of selective vulnerability: some neurons, like those in the CA1, are more sensitive to ischemic insult. Why? Good question.

At the WSU Emergency Medicine Cerebral Resuscitation  Laboratoy, we have traditionally been primarily interested in transient global brain ischemia, although we have recently begun investigations into focal brain ischemia as well.