Sildenafil Increases Exercise Capacity in Low-Oxygen Settings

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The summary below is from the full report titled "Sildenafil Increased Exercise Capacity during Hypoxia at Low Altitudes and at Mount Everest Base Camp. A Randomized, Double-Blind, Placebo-Controlled Crossover Trial." It is in the 3 August 2004 issue of Annals of Internal Medicine (volume 141, pages 169-177). The authors are H.A. Ghofrani, F. Reichenberger, M.G. Kohstall, E.H. Mrosek, T. Seeger, H. Olschewski, W. Seeger, and F. Grimminger.

What is the problem and what is known about it so far?

The alveoli are the parts of the lung in which oxygen transfers from air to blood. When the amount of oxygen in air is reduced, changes occur in the lungs and heart to compensate for the low oxygen at the alveoli. These changes, which include constriction of the blood vessels in the lung, decrease a person's ability to exercise. High altitude is one situation where the amount of oxygen in air is low. The low oxygen and resulting changes in the heart and lungs account for many of the symptoms that people develop when they go from low to high altitudes. Sildenafil, a drug that has become a popular treatment for erectile dysfunction, causes the blood vessels of the lung to dilate (become wider). Previous studies have shown this effect of sildenafil in patients breathing air mixtures with low oxygen content at sea level. These observations have led experts to speculate that sildenafil might help prevent some of the problems with exercise ability caused by other conditions of low oxygen. One such condition is high altitude.

Why did the researchers do this particular study?

To explore the effects of sildenafil on exercise capacity in people exposed to low oxygen at high altitude.

Who was studied?

14 healthy adults who were experienced mountain climbers.

How was the study done?

The researchers assigned the study participants to receive sildenafil or a placebo pill in random order and measured their exercise capacity in 2 situations: 1) low altitude while breathing a mixture of air that contained only 10% oxygen and 2) high altitude at the Mount Everest base camp.

What did the researchers find?

Sildenafil reduced high pressures in the lung's blood vessels at rest and with exercise and increased maximum exercise capacity in both settings.

What were the limitations of the study?

The results of this small study are preliminary. Additional studies are needed to determine whether sildenafil would be helpful in acute mountain sickness.

What are the implications of the study?

Sildenafil might be useful in managing acute mountain sickness or other conditions caused by low oxygen levels at the alveoli.