Hello, Thanks for the query to H.C.M. Forum. Mechanical aortic valve , but from ,how many years? Warfarin and aspirin both are anticoagulant so will prevent embolism formation in lungs. Exposure to high altitude in association with severe exertion ( physical due height )is well recognized setting for formation of PULMONARY EDEMA. How, pulmonary edema develops exact mechanism is not known till now, only hypothesis is there. One thing is clear that at high altitude person develops HYPOXIA ( less amount of oxygen in lungs and also in blood). This type of HYPOXIA is cured by either by oxygen supply or by reaching at low altitude. Hypoxia don t alter permeability of the alveolar-capillary membrane ( in lungs). So due to this hypoxia ( for compensation to reduced amount of oxygen in lungs ) heart have to work extra i.e. cardiac output increases , so also pulmonary arterial pressure. Due to high, altitude and exertion there develops pulmonary arterial constriction and hence edema , which is very lethal and cause of death at high altitude. Before this expedition, please get in drugs which abolish pulmonary edema. Hope I have answered your query. If further any question I will help. Good luck for journey. Dr. HET