BRIDGET HARRIS lies on a hospital bed with a nylon hood covering her head. As cold air streams from the hood and over her scalp, her lips gradually turn blue and her speech slows. Within an hour, her core body temperature has dropped by 0.5 °C, but she remains comfortable. “The airflow is almost relaxing,” she says. “It sounds like white noise.”
Harris, a PhD student at the University of Edinburgh, UK, is testing her own invention: a cooling helmet designed to induce mild hypothermia.
We all know that a cool cloth applied to the forehead can ease a headache, but now researchers like Harris are investigating whether technologies that cool the brain itself could prevent brain damage following a stroke or cardiac arrest. Similar techniques could also protect the heart and kidneys from damage during surgery.
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.
Harris’s hood, for example – developed with her supervisor Peter Andrews and medical technology company KCI of San Antonio, Texas – exploits the dense network of blood vessels on the scalp that carries blood to the brain. The device consists of two nylon sheets that fit around the head, one on top of the other, with small perforations in the layer closest to the skin. When cold air is blown between the two sheets, these perforations allow it to penetrate to the skin at regular intervals across the scalp, cooling the blood vessels. “It’s a bit like a hairdryer hood – it doesn’t cover the face and one lies with one’s head inside it,” says Harris. …