Haemostasis at high altitude.

Haemostasis has been studied by several authors during exposure to altitude hypoxia. On acute induction to hypoxia, platelet count, platelet aggregability and bleeding time are normal; an increase of thromboxane released from platelets and of prostacyclin, released from endothelial cells is observed; coagulation factors are unchanged except of F. VIII which is increased; modified antithrombin III (ATm) are normal; fibrinopeptide A is increased in subjects with pulmonary edema and fibrinolytic activity after venous occlusion is normal. In chronic hypoxia, during a stay at 6542 m (Mt. Sajama), we found in 7 subjects an important increase in D. Dimer (p < 0.001) that seems to correspond to an activation of coagulation and a decrease of F. VIII R. Cof/F. VIII R. Ag ratio which suggests an endothelial cell damage.