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Friday, April 26, 2013

NEWS and COMMENT: Back from the Dead [Full link to blog for email clients.]

Can a medical procedure "resurrect" a person who is clinically dead?

Dr. Sam Parnia says yes.  []

I saw references to the article via three different sources - New Scientist RSS feed, Instapundit and through my friends at Baen's Bar.  It's a fascinating subject, and one I couldn't wait to cover - except for the fact that I already had content scheduled.  So, it may be a week or so after the fact, but here goes:

To quote the article:
[Dr. Sam] Parnia is head of intensive care at the Stony Brook University Hospital in New York. If you'd had a cardiac arrest at Parnia's hospital last year and undergone resuscitation, you would have had a 33% chance of being brought back from death. In an average American hospital, that figure would have fallen to 16% and (though the data is patchy) roughly the same, or less, if your heart were to have stopped beating in a British hospital.
How is this possible?

Well, many years ago, I was discussing the effects of cerebral ischemia with a colleague.  Ischemia results when blood flow is blocked and oxygen delivery to the cells is reduced (or stopped).  Some tissues are more sensitive to low oxygen, and some are less sensitive.  Muscle tissue contains stores of glucose and oxygen that allows it to function with lowered oxygen - they have to, because some exertion requires more energy in "real-time" than can be supplied by the blood.  The brain doesn't have those stores, and within 5 minutes of low/no blood flow, the sensitive neurons begin to die.

"But even then," my colleague informed me, "the problem is less about the lack of blood flow and oxygen, but what happens when the blood flow is restored!"  Sudden restoration of blood flow causes neurons to release potassium and calcium which in turn can be toxic to neurons if they build up in the fluid around the cells.  [See: for details of the delicate chemical balance needed for brain cell function.] Neurons require glucose, oxygen and water in order to function, but they also need the blood to flow and remove lactic acid, CO2 and other metabolic products. an aside, cells in our bodies break down glucose via the Citric Acid Cycle (or Krebs' Cycle).  The result is not actually very much of the energy molecule ATP, but rather a lot of intermediate products which are then metabolized via "oxidative phosphorylation" (OXPHOS) to form ATP.  OXPHOS requires oxygen; when oxygen supplies are low, such as during prolonged exertion or exercise, ATP can still be produced in lower quantities, leading to increased CO2 and lactic acid byproducts.  It is the lack of ATP and the buildup of lactic acid that produces fatigue and muscle pain. Reduced blood flow (ischemia) and consequent reduced oxygen is responsible for the sharp chest pains of a heart attack.

So, the solution to surviving the cessation of the heart beat is to keep the brain (and body) oxygenated.  It also helps to provide a means of removing the metabolites.

A key element of Parnia's work is hyperbaric oxygen therapy - not just increasing the concentration of oxygen in the air, but increasing the air pressure as well to force more oxygen to the tissues.  A colleague of mine has demonstrated that hyperbaric oxygen improves the rehabilitation after a stroke as long as it can be applied within 30 minutes of the stroke.  It is his goal to get hyperbaric chamber-equipped ambulances into common use to aid stroke victims.

A second element of "resurrection therapy" is to keep blood flowing.  Parnia uses an "extracorporeal membrane oxygenator" (ECMO) to oxygenate the blood, coupled to what is commonly termed a "heart-lung machine" to provide pressure to the blood and force it through the circulatory system.  Another technique is an LVAD - left ventricular assist device - which assists the heart in pumping blood and is becoming a common therapy for heart disease in which the left ventricle is unable to produce enough pressure to keep the blood moving to all tissues. While intended only to assist the heart until a more permanent solution (i.e. heart transplant) can be performed, LVADs are quite effective in maintaining life - to the point that one patient with an LVAD was found to eventually have no heartbeat at all!  The patient's own heart had failed, but the LVAD kept the blood flowing!  [].

The third major element of preserving the "life" in living tissue is cooling.  It is very well known that cooling of the body slows down the enzymes that break down cells - so if we couple oxygen, circulation and cooling, we have a way to suspend the breakdown of neurons until normal blood flow and oxygenation can be restored.

Sam Parnia claims we need a new definition of death:  even "clinical dead" is not irreversible as long as the cells can be maintained and revived.  But what about the "mind" and "soul"?  Frankly, the latter is beyond my capacity to answer, but as to the former, suspending the activity of neurons - or even not suspending it, since we are providing support therapy in the form of oxygen and blood flow - is not much different than going into low activity states of unconsciousness or coma.  The mental capability after "resurrection" is dependent only on how much degradation was allowed to occur - minimize that, and the effects of "death" are also minimized.

It is a heartening outcome, and may mean that stroke and traumatic brain injury are much more treatable than previously thought.  It probably won't prolong life or reverse the effects of aging, but will preserve it from a premature end.

In the meantime -  let's all try our best not to become test cases for Resurrection Therapy!

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