I often lecture to my 100-level classes on human adaptations to altitude and the effects of hypoxia. Our picture of these adaptations and other physiological changes associated with high altitude has been changing in recent years. One reason is a better assessment of the variability among high-altitude populations in their response to hypoxia.
The other reason is better technology. The "Mind Matters" feature of the Scientific American blog has a feature this week on the neuroscience of altitude sickness. It details some of the effects of hypoxia on the brain, including details from recent studies involving MRI scans of elite climbers:
This acute high-altitude disease has long been known to cause brain damage. But one of the sobering things about the Fayed study is that none of the Everest climbers experienced high altitude cerebral edema, and the only acute case of mountain sickness was a mild one suffered by the expedition's amateur climber. Yet even all the professional mountaineers showed lasting brain damage -- presumably suffered on previous ascents to the high mountains, because their MRI scans were abnormal before the Mt. Everest ascent and unchanged after.
The essay is by R. Douglas Fields, describing work by Nicholas Fayed and colleagues. The results are true not only for Everest but for lower-altitude summits as well. The first discussed is Aconcagua:
The body is remarkably resilient--does the brain recover from these mountaineering wounds? To answer this important question, the researchers re-examined the same climbers three years after the expedition, with no other high-altitude climbing intervening. In all cases, the brain damage was still evident on the second brain scan.
Still, Aconcagua is one of the world's highest mountains -- in the top 100. Mont Blanc, in the Alps, is less extreme. With a summit at 4810 meters, it is climbed each year by thousands of mountaineers who probably do not expect injury to their "second favorite organ," to use Woody Allen's nomenclature for the brain. Yet the researchers found that of seven climbers reaching the summit of Mount Blanc, two returned with enlarged VR spaces.
Of course, if you've seen any of the various Everest documentaries, you will remember the cognitive impairment that results from low oxygen. Climbers often can't think straight, and particularly inexperienced climbers really need someone at a lower altitude to help supervise their summit attempts. But the sobering thing about these MRI results is that the altitude of Mont Blanc is substantially lower than the Everest base camp at 5500 meters.