Prevention of High Altitude Pulmonary Edema

A double-blind placebo controlled study * To compare the effect of tadalafil and dexamethasone versus placebo on Ppa and pulmonary edema formation in subjects susceptible to HAPE. * To investigate the effect of dexamethasone on alveolar fluid clearance, as assessed by measurement of the nasal potential difference, and prevention of HAPE. * To investigate the effect of the tadalafil and dexamethasone versus placebo on the dynamic CBF autoregulation properties and on the development of AMS in HAPE susceptible subjects.