Brain - Cooling Techniques

Scientists and physicians are developing new brain - cooling techniques to reduce morbidity after heart attacks (and presumably strokes) and to aid successful resuscitation after heart attacks. One device, like a reverse hair drying hood, cools the scalp and its blood vessels, achieving about 1 degree C cooling of the brain per hour. Another device sprays a refrigerant deep into the nose to indirectly cool arteries passing nearby, heading for the brain. The nasal device cools the brain by 2.4 degrees C per hour. A third device uses an icy slurry lavage into lung airways, to cool blood passing into the carotid arteries to the brain.

For some time, doctors have observed that cooling patients following a heart attack can reduce brain damage. Although they are not yet sure of the mechanism behind this effect, researchers suspect that cooling the brain by 4 °C, to around 33 °C, reduces the metabolism of brain cells, reducing their hunger for oxygen for the crucial moments during which blood is in short supply. Damage seems to be reduced even if the brain is only cooled once the heart has been restarted, suggesting that cooling may also slow the release of toxic chemicals from neurons and glial cells - a process called the ischaemic cascade, which triggers further brain-cell death up to 24 hours after a cardiac arrest or stroke.

Previously, doctors have induced "therapeutic hypothermia" by applying ice packs or cooling blankets to the whole body, or injecting cold saline solution into the veins. However, cooling the whole body can increase the risk of infection and pneumonia, so researchers are now building targeted devices that chill the brain directly.

...The ice slurry can cool the brain by 4 °C - the safe limit before damage is risked - in less than 15 minutes, says Kasza, who has so far tested the technique on pigs. His team is investigating whether their icy slurry could also be applied to the kidneys (see picture) and the heart during invasive surgery, to prevent damage to the organs when blood flow is suspended for the operation.

One of the main advantages of all the new techniques is that they are simple enough to apply before or immediately after resuscitation following a heart attack - minimising the delay between the heart malfunction and cooling the brain. "A paramedic could deliver the slurry," says Kasza.

What's more, a recent study in pigs suggests that immediate cooling with the RhinoChill device, besides reducing brain damage, could also improve the chances of success of the resuscitation itself, although it is not yet certain why this is. Sixteen pigs were given a heart attack, and then left for 15 minutes before CPR was applied to start their hearts again. Of the eight pigs cooled using the RhinoChill system during CPR, six survived, compared with just two of the eight who were left unchilled (Resuscitation, DOI: 10.1016/j.resuscitation.2008.03.087).

Rapid application of such techniques could be particularly good news for stroke victims. "Clot-busting drugs can only be administered after diagnosis and brain scans in the hospital," says Andrews. "But applying therapeutic cooling at the scene of the stroke could lengthen the time window in which the drugs are effective - before too much damage has occurred," he says. _NewScientist

These techniques are a far cry from the advanced cryonics and vitrification methods needed for long - term organismic storage or hibernation. But experiments with them, and experience using them should add to the knowledge needed to develop the longer - term methods.