TUESDAY, Dec. 16 (HealthDay News) -- It's a potentially lethal gas, but small amounts of carbon monoxide (CO) may help prevent brain damage after a stroke, Johns Hopkins researchers report.

CO, a colorless, odorless gas that can cause organ damage and death, is found in combustion fumes, such as those made by heating systems, vehicles and gas ranges. In enclosed or semi-enclosed places with poor ventilation, CO can build up and pose a serious threat.

The Hopkins team found that low amounts of inhaled carbon monoxide reduced brain damage by as much as 62.2 percent in mice with strokes induced by briefly blocking an artery to one side of the brain. The researchers believe that CO can protect nerve cells from damage.

"CO is made naturally by the body and can serve a protective function under various circumstances. The idea for our experiment was to see if external CO could have a similar effect," study author Sylvain Dor, an associate professor in the department of anesthesiology and critical care medicine, said in a Hopkins news release.

After strokes were induced in the mice, they were exposed to either 125 parts per million (ppm), 250 ppm of CO, or air. Each group of mice was tested for post-stroke brain damage and function, mainly by observing their running patterns and reactions to certain stimuli.

Brain damage in the side of the brain where blood supply was cut off was 49.9 percent in mice exposed only to air, 33.9 percent in mice exposed to 125 ppm of CO, and 18.8 percent in mice exposed to 250 ppm of CO. Compared to those exposed only to air, the mice exposed to CO had significantly better neurological function test scores.

The protective effect was evident in mice treated at both one and three hours after stroke. This is an important point, because "many stroke victims will not receive immediate treatment," Dor said.

The researchers said CO's protective effect may be due to:

• Its ability to dilate blood vessels, which increases blood flow.
• Its anti-inflammatory properties, which prevent cell death by inflammation.
• Its capacity to reduce water in the brain. Excessive water in the brain increases intracranial pressure, which kills brain cells.

The study was published in the Dec. 15 online issue of Neurotoxicity Research.

Each year in the United States, about 700,000 people have a stroke. Of those, 87 percent suffer an ischemic stroke, caused by a blocked artery.

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