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Only one mountain pushes lungs to the absolute limit -- Mount Everest -- and only once has that limit been measured directly, by .

He made the ascent as the respiratory physiologist on a science and mountaineering expedition led by Sir Edmund Hillary in 1960-1961.

The measurement West took of himself at an elevation of about 24,000 feet as they wintered at a camp set up at 19,000 feet still stands today as the highest recorded maximal oxygen consumption.

"I used to put it in my CV actually," he said.

After using supplemental oxygen, a , proving it possible that human lungs could manage in the thin air at such an elevation.

But how was a mystery, as West explained at a lecture honoring him at the American Thoracic Society meeting last month.

"If you extrapolate this line, which relates maximal oxygen consumption to the barometric pressure ... you get a very interesting prediction," he said. "It looks as though all the oxygen available is going to be required for the base oxygen uptake [at rest]. The body takes a certain amount of oxygen to keep the brain ticking and the heart pumping. So how is it that people can get to the summit of Everest without supplementary oxygen?"

A subsequent expedition by his team in 1981 uncovered the extraordinary physiologic changes that allow this feat.

Alveolar gas samples were collected right at the summit of Everest, then analyzed on special equipment developed for that purpose in West's lab at the University of California San Diego.

Both the partial pressure of oxygen (PO₂) and partial pressure of carbon dioxide fall with altitude, but at a certain altitude PO₂ stops falling due to being insulated by an extreme degree of hyperventilation. Arterial pH on the morning after the summit climb was 7.7 to 7.8, and that high pH increases the affinity of oxygen for hemoglobin.

"It's an extraordinary coincidence, a cosmic coincidence, that the summit of Mount Everest is right at the limit of human tolerance to hypoxia," West noted. "If you have an evolutionary reason for that, I'd like to hear about it."

"We are still waiting for someone to go and make measurements again. These are only data we have," he said.

That West was involved in the expeditions at all appeared to be sheer chance, he noted.

While sitting in a conference almost 60 years ago, the person sitting next to West "asked did I know that Sir Edmund Hillary was organizing an expedition to the Himalayas that would combine scientific work with mountaineering and would I be interested in going on as a physiologist?"

West had no prior experience with either high-altitude physiology or mountaineering.

During his interview for the position, Hillary asked, "'Well, John, how much mountaineering have you done?'" West reminisced.

"I said, 'I'm afraid not any at all' -- that doesn't sound so good. He said, 'Why don't you climb up that flight of stairs?,' which I did, and he said, 'Well, that's okay.'"

It was "one of most serendipitous events of my career," he told conference attendees.

"Embrace serendipity, and if you do, wonderful things can happen," he advised.

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