Altitude sickness is caused by an increase in capillary blood pressure in susceptible individuals, a study has revealed.
The research by Marco Maggiorini and colleagues at Zurich University, Switzerland, shows for the first time the trigger of a potentially life-threatening condition that poses a serious threat to mountain climbers.
It also suggests a way to treat high-altitude pulmonary edema (Hape) - using a vasodilator, a substance that causes blood vessels to dilate, to lower capillary pressures to more normal levels.
"The condition is strictly related to a lack of oxygen in the air when climbers or hikers reach certain altitudes. As soon as you give oxygen or a vasodilator, the pressure goes down," Maggiorini said.
In research published in Circulation: Journal of the American Heart Association , 30 climbers were tested. Sixteen had previously experienced Hape, which makes its sufferers extremely listless and can make them cough up blood.
The subjects had the blood pressure in their pulmonary arteries, which carry blood from the heart to the lungs, and the permeability of the pulmonary capillaries measured at 490 metres above sea level and again at 4,559 metres.
The scientists found that the Hape-susceptible individuals had a higher constriction in their pulmonary blood vessels compared with the control group at low altitude. At high altitude, they had higher average pulmonary artery pressure (37mm Hg compared with 26mm Hg) and capillary pressure (19mm Hg compared with 13mm Hg).
However, there was no difference in permeability.
Maggiorini said that vasodilators may be used to prevent Hape as well as to treat it.
"Mountaineers may want to use vasodilators before they travel to areas such as the Alps, the Rocky Mountains, the Himalayas, the Andes or other high altitudes," he said.