"We have known that both tadalafil and dexamethasone are good for preventing high altitude pulmonary edema (HAPE) and dex for treating symptoms of acute mountain sickness (AMS)," said lead authors Dr Manuel Fischler, of the University Hospital in Zurich, Switzerland, and Hans-Peter Brunner-La Rocca, of the University Hospital in Basel, Switzerland.
"But we did not know whether they could also improve exercise capacity at altitude by reducing pulmonary hypertension, one of the important factors in altitude-related exercise limitations," they added.
During the study, the researchers recruited 23 mountaineers with a history of HAPE and administered baseline cardiopulmonary exercise tests a low elevation (490 meters, or 1607 feet).
Subjects were tested for oxygen uptake kinetics by pedaling a stationary bike at a constant rate for six minutes, and then for exercise capacity by pedaling at 50 percent of their predicted maximum workload for one minute, then increasing output by 25 percent each additional minute until exhaustion, usually after 8 to 12 minutes.
"At low altitude, peak exercise performance of subjects was significantly above age- and gender-adjusted normal values, indicating superior fitness in these subjects," noted Dr. Fischler.
All participants were randomised to take tadalifil, dexamethasone or placebo, beginning the day before a cable-car ascent from Alagna, Italy, at 1,100 meters (3,609 feet), to 3,200 meters (10,499 feet).
They then ascended on foot to Capanna Gnifetti at 3,650 meters (11,975 feet). After an overnight stay at Capanna Gnifetti, the climbers finally ascended to Capanna Regina Margherita at 4,559 meters (14,957 feet).
The cardiopulmonary exercise tests were performed 4-5 hours after arrival, and echocardiographic examinations were performed the next day.
"Reduced oxygen content in the air is the major limiting factor at high altitude. Reduction in exercise capacity goes in parallel to the reduction in oxygen up to an altitude of approximately 4000 meters. At higher altitudes, there is an even further reduction in exercise capacity," said Dr. Fischler.
"As expected, exercise capacity at high altitudes was diminished among all groups and key indictors of cardiopulmonary stress were elevated," he added.
Both tadalafil and dexamethasone subjects showed a smaller drop in oxygen saturation over the placebo group, indicating a better uptake of oxygen, and a measure of pulmonary artery pressure was significantly less for both tadalifil and dexamethasone groups over placebo.
"Our study indicates that for HAPE-susceptible climbers, taking dexamethasone improved exercise capacity, oxygen uptake kinetics and decreased the anaerobic threshold," said Dr. Fischler. "Overall, this means that those climbers who took dex felt better, were able to do more, and probably experienced fewer altitude-related discomforts than both other groups."
The study appears in American Journal of Respiratory and Critical Care Medicine.