Blood coagulation changes at high altitude predisposing to pulmonary hypertension.

Blood coagulation studies were carried out in 38 Indian soldiers who were resident at altitudes between I2,000 and i8,0oo feet for 2 years. Compared with I6 sea-level controls, 6 of these 38 subjects who had developed pulmonary hypertension during their stay at high altitude showed a significant increase ofplasmafibrinogen,fibrinolytic activity, platelet adhesiveness, plateletfactor 3, factor V, and factor VIII. In the remaining 32 subjects who did not develop pulmonary hypertension there was a significant increase of plasma fibrinogen and fibrinolytic activity only. The above differences between subjects who develop pulmonary hypertension at high altitude and those who do not develop pulmonary hypertension suggest that high altitude pulmonary hyper- tension is of occlusive origin and is dependent on changes in blood coagulation at high altitude.