American Stroke Association meeting report
SAN DIEGO, Feb. 5 – Helmets that cool the brain may minimize stroke damage, according to two small studies presented today at the American Heart Association's 29th International Stroke Conference.
In a Japanese study, a "helmet-type cooling apparatus" was tested on 17 patients with severe ischemic stroke. An American study tested a "NASA-spinoff" helmet on six patients with severe ischemic stroke.
Ischemic strokes are caused by blood clots in blood vessels of the brain or leading to it.
The helmets may improve patient outcomes and lengthen the time treatment window for ischemic strokes.
Hypothermia – low temperature – is known to protect the brain from ischemic injury. However, overall surface cooling is associated with various adverse effects, said Kentaro Yamada, M.D., of the National Cardiovascular Center in Osaka, Japan.
"The largest problem of systemic surface cooling is the requirement of general anesthesia, which increases risks of respiratory and circulatory diseases," he said. "Systemic surface cooling is commonly associated with severe infections, arrhythmia, hypopotassemia (low potassium) or decrease of platelet counts, which may countervail protective effects of hypothermia."
He also noted that "in our experience of hypothermia therapy in acute stroke patients using systemic surface cooling, excellent functional recovery was obtained in 83 percent of younger patients under age 60 but only in 20 percent of elderly patients."
Scientists have tried various methods to cool the brain, including cooling the entire body, using dry ice and blowing cool air on the head. However, methods were unable to selectively cool the brain rapidly and maintain such preferential cooling over the rest of the body, said Huan Wang, M.D., assistant and resident of neurosurgery at the University of Illinois, College of Medicine, Peoria, Ill.
He said it is well known that "brains like to be cold." Stroke and head trauma patients fare worse when they are running fevers. However, the same is not true for the rest of the body, including the heart and immune system, which do better at normal temperatures, Wang said.
Yamada and colleagues tested the helmet on patients (average age 68) three to 12 hours after stroke onset. The helmet was attached to the head and neck. The cooling of the head continued non-stop for three to seven days without anesthesia.
Researchers evaluated functional outcome three to 10 months after stroke. The surface cooling was performed successfully in all patients.
Tympanic temperature, which measures surface brain temperature, was lowered 4.0 degrees Fahrenheit and jugular temperature, which reflects deep brain temperature, was lowered 1.4 degrees Fahrenheit. In hypothermia with a helmet, such a temperature gradient in the brain results because of the local nature of the cooling method, Yamada said.
Some patients experienced mild shivering, elevated potassium levels, mild skin damage and infections, but none had serious adverse effects.
After 10 months of follow-up, only one patient (6 percent) had died. Six patients (35 percent) had "good" functional outcome three to 10 months after stroke.
The American study evaluated patients average age 68 and used liquid cooling technology developed by NASA scientist William Elkins, "father of the American spacesuit," Wang said.
In animal studies, researchers have determined that cooling the brain can reduce the damage that stroke does to the brain tissue by as much as 70 percent, Wang said. "The goal with this therapy, therefore, is to try to improve neurological outcomes by minimizing stroke's effect," Wang said. "The first step in that direction was to find a therapy that effectively cooled the brain and, judging by this study, we have."
In this study, researchers gauged brain temperature via tiny fiberoptic probes inserted in the brain. These probes are often used to monitor vital brain functions of stroke patients in intensive care. The patients had neurological deterioration despite being treated for brain swelling.
Researchers took patients' brain temperatures at the start of the study (before patients put on the helmets) and throughout the next 48 to 72 hours. They found that the helmet preferentially cools the brain much more rapidly and profoundly than it does the body. The patients' brains cooled an average of 6 degrees Fahrenheit the first hour, without dropping body temperature significantly. Then, the helmet continued cooling the brain, while cooling body temperature at a much slower rate. Researchers were able to use the technology an average of six to eight hours before body temperature dropped below 97 degrees F. Five patients tolerated the helmet cooling well. One 85-year-old woman with a previous heart arrhythmia experienced an abnormal heart rate but responded promptly to treatment.
The study did not report patient outcomes, but Wang said the treatment has great potential. If EMS personnel can use the helmet in the field, they theoretically can lengthen the time that a stroke patient is eligible for clot-busting therapy. "We believe that if you keep the brain tissue cool, you will have a longer tissue survival time. Then, when we open the artery, we could salvage much more brain tissue and hopefully avoid adverse neurological effects," Wang said. "Rapid and selective brain cooling is a simple but elegant strategy that has been shown to limit injury in stroke, brain trauma and cardiac arrest," said Vinay Nadkarni, M.D., immediate past chair of the American Heart Association's emergency cardiovascular care committee. "Building upon space-age technology, this novel technique is a good example of how bright scientists and innovative industry technologists can collaborate to speed the delivery of emergency cardiovascular care interventions. This device, and others like it, may have wide applicability in the field."
Source: Eurekalert & othersLast reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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