Nitric Oxide Is Key to High Altitude Function -- MEDICA - World Forum for Medicine
Picture: Potala Palace in Lhasa 
Genes might be a reason for
the Tibetans´ high NO levels
© Claus Bünnagel/Pixelio

The question why some people can live at high altitudes and thrive while others struggle to obtain enough oxygen to function can now be answered, at least for Tibetans who live at altitudes around 14,000 feet. They have increased nitric oxide (NO) levels.

High levels of NO circulate in various forms in the blood and produce the physiological mechanisms that cause the increased blood flow that maintains oxygen delivery despite hypoxia—low levels of oxygen in the ambient air and the bloodstream. Researchers from Case Western Reserve University and the Cleveland Clinic report that Tibetans have ten times more NO and have more than double the forearm blood flow of low-altitude dwellers.

The low barometric pressure of high altitudes generally causes low arterial oxygen content among Tibetans, yet the researchers have found that Tibetans consume oxygen at normal rates. “We asked how that could be done,” said Cynthia Beall, the S. Idell Pyle Professor of Anthropology at Case Western Reserve University. Beall collected blood samples and blood flow readings from the forearms of 88 Tibetans during a 2002 research trip. For comparison, the scientists collected the same information from 50 near sea-level dwellers from the United States.

The combined increase in NO and blood flow levels resulted in double the amount of oxygen delivered to the capillary beds in the Tibetans’ arms. The researchers hypothesize that Tibetans have a genetic mutation that allows high NO production.

During the study, the researchers also recognized another population difference: Tibetan women were found to have higher nitrite and lower nitrate levels than those of Tibetan men, whereas no gender differences were found in sea-level dwellers.; Source: Case Western Reserve University