10-16 May 2013 #655

Mastering the mountains

Why Sherpas are physiologically so well-adapted to performing arduous tasks like fixing ropes at high altitudes?
Dhanvantari by Buddha Basnyat, MD

News of the fist fight between the Sherpas and three international Alpine-style climbers on Mount Everest left the world astounded this past week. Many versions of the event emerged in the media debating how and why the brawl happened and its effect on mountaineering and tourism in Nepal. But in this column we will focus on what makes Sherpas physiologically well-adapted to performing arduous tasks like fixing ropes at high altitudes.

The difference in the adaptive mechanism between high altitude Tibetans (from whom the Sherpa people derive their ancestry) and the recently-settled Han Chinese in the Tibetan plateau (4,500m) is enormous. Tibetan women generally have uncomplicated pregnancies in Tibet compared to the relatively complication-ridden pregnancies of the Han Chinese. In fact this problem is so acute that most expectant Han Chinese mothers move to lower altitudes for safer delivery. Even before birth, people of Tibetan origin are better adapted to hypoxia (low oxygen).

Furthermore, infants born to Han Chinese parents may have pulmonary hypertension (increased blood pressure in the blood vessels of the lungs) leading to heart failure. This condition is seldom seen in a newborn Tibetan infant. If a Han Chinese infant survives the first few years, she finds herself at greater risk of chronic mountain sickness (CMS). Unlike acute mountain sickness (AMS) which we see regularly in the Himalaya, CMS is caused by excessive production of red blood cells and may lead to heart failure and strokes due to ‘sludging’ in the circulation of blood.

From intrauterine life to infancy to adulthood, Tibetans seem to have a protective mechanism that helps them cope with altitude. By combining this natural flair with training, they are able to perform difficult tasks like putting up ropes and setting up camps and are by far the best high altitude workers.

These physiological findings have been corroborated by the molecular discovery by Peter Ratcliff and Greg Semenza (both will probably share the Nobel prize soon) of the potentially protective hypoxia inducible factor (HIF) gene. According to a flurry of recent medical reports people with Tibetans ancestry possess this HIF gene, but not the Han Chinese. No wonder the Sherpas are the ultimate masters of the mountains.

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