Altitude and hypoxia have been implicated as stimulting coagulation and the risk for thrombosis. However, previous studies were either uncontrolled field studies or used extreme environmental conditions. Since exertion is known to affect hemostasis, we sought to control for this factor by using a standardized exercise-hypoxia protocol. We exercised 10 subjects using a treadmill, and obtained samples at baseline, after hypoxic exposure, and at maximal oxygen consumption (V02Max) both at room air and with 12% oxygen (equivalent to 14,000ft [4600m] altitude). At room air (21% FIO2) at 100% VO2Max we found no significant change in platelet count when compared to baseline (212,000112,00 to 211,000±4,00/uL), but a rise in mean platelet volume (mpv) (8.8±.2 to 9.5±.2 fl), reticulated platelets (1%0±.1 to 2.4%±.48) von Willebrand's antigen (109±9 to 201±21 lU/ml), Factor VIII activity (132115 to 38818 lU/ml), F1.2 (0.91.3 to 2.21.5 nmol/L), and D-dimers (147129 to 599913600 nmol/L) plus shorting of the euglobulin clot lysis time (EGCLT) by 72%. Exposure to 12% FiO2 for 30 minutes resulted in a modest rise in platelet count (209,000+10,000 to 223,000±7,000/uL), and reticulated platelets (1.0±.3 to 1.710.8%) but no changes in factor VIII or von Willebrand antigen. F1.2 did increase from 0.5111 to 1.41.66 nmol/L but there was wide individual variation. D-dimers did not change but the EGCLT shortened by 32%. With hypoxic exercise to VO2max there were further increases from baseline in platelet count (266,000±14,000/uL), and reticulated platelets (2.8±1.1%). Factor VIII (272146 IU/ml)and von Willebrand's antigen (170118 lU/ml) rose with hypoxic exercise but the effect was less dramatic than with exercise alone. There was no increase in F1.2. D-dimers increased only slightly (200138 nmol/1) but the EGCLT shortened by 80%. Thus, it appears that moderate hypoxia may exert an antithrombotic effect by both damping exercise induced procoagulant changes and stimulating fibrinolysis.
|Original language||English (US)|
|Issue number||11 PART II|
|Publication status||Published - 2000|