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Medical lessons learned at the heights of Mount Everest could change the way physicians treat critically ill patients suffering from low oxygen levels.

An expedition led by doctors from University College London set out to prove what has long been suspected - that mountain climbers have incredibly low levels of oxygen in their blood because of the thin air at such high altitudes.

A short distance from the top of Everest - where the temperature dipped to -25 C and the wind howled at 20 knots - four of the climbers unzipped their down suits so that blood could be drawn from the femoral artery in the groin.

The measurements, published in this week's edition of the New England Journal of Medicine, were so low that they surprised even the researchers. The average arterial oxygen level was just 3.28 kilopascals. (A kilopascal is a measure of the oxygen pressure in the blood and reflects oxygen's ability to enter body tissues.) That's the lowest level recorded in humans, said team leader and mountain climber Mike Grocott.

The normal reading is between 12 and 14 kPa in healthy adults. When patients experience levels below 8 kPa they are considered to be critically ill and in need of oxygen therapy.

And yet the Mount Everest climbers were able to function despite their extremely low oxygen levels.

"Obviously, it is a measurement made in unusual people and in an unusual place," Dr. Grocott said. But he believes the finding could lead to better care for heart and lung patients, premature infants and others afflicted with low oxygen levels.

Dr. Grocott noted that oxygen therapy can be life-saving but also carries certain risks. For instance, giving patients pure oxygen produces an abundance of free radicals, unstable molecules that can damage healthy cells. Furthermore, mechanical ventilation puts potentially harmful pressure on delicate lung tissues.

He speculated that critically ill patients, just like mountain climbers, may be able to survive with lower oxygen levels than once thought. "This raises the possibility that we could cause less harm" by treating the patients with less oxygen, Dr. Grocott said. Studies, he added, would be needed to test the new approach.

THIRD-HAND SMOKE?

There's no doubt you've heard about the potential health risks of inhaling second-hand smoke from someone else's cigarette, cigar or pipe. But how about the dangers of third-hand smoke?

Researchers have coined the new term to draw attention to the risks posed by toxic smoke particles that cling to surfaces, clothing and hair long after the smoke has cleared from the air.

The leader of the research team, Jonathan Winickoff of Massachusetts General Hospital, stressed that the dangers of third-hand smoke are real - especially for young children who crawl on the floor and may ingest the particles when they put their hands in their mouths.

Smoke residue contains numerous dangerous substances, including harmful metals, cancer-causing compounds and even radioactive materials.

Writing in the journal Pediatrics, the researchers emphasize that parents can't protect their kids from third-hand smoke by the same measures normally used to limit exposure to second-hand smoke - opening windows, turning on fans or simply waiting for smoke to dissipate.

They say what's really needed is a ban-the-butt approach wherever non-smokers congregate - and that includes the family home. They hope greater awareness of the risks of third-hand smoke may convince more smokers to accept such bans.

MENTAL AEROBICS

What's good for the body is also good for the mind - and exercise, in particular, appears to help keep both in top form.

Previous research has shown that as people age there is a progressive decline in blood flow to the brain, which can contribute to mental impairment.

A new study involving 42 Calgary women, with a mean age of 65, found that those who took part in regular aerobic activity had better blood flow than those who were inactive.

And equally important, the exercisers scored 10 per cent higher on cognitive function tests than their sedentary counterparts, according to the findings published in the journal Neurobiology of Aging.

"The take-home message from our research is that basic fitness - something as simple as getting out for a walk every day - is critical to staying mentally sharp and remaining healthy as we age," said Marc Poulin, an Alberta Heritage scientist at the University of Calgary.