Orthostatic hypercoagulability: a novel physiological mechanism to activate the coagulation system

Area of Science:

• Physiology
• Hematology
• Cardiovascular Science

Background:

• Orthostatic stress leads to plasma shifts and increased pressure in lower extremities.
• This can cause endothelial activation and elevated plasma protein concentrations, potentially including coagulation factors.

Purpose of the Study:

• To investigate the hypothesis that standing activates the coagulation system.
• To identify changes in coagulation factors and endothelial activation markers during orthostatic stress.

Main Methods:

• 18 healthy volunteers underwent hemodynamic monitoring, plasma shift estimation, and blood tests.
• Coagulation tests included fibrinogen, factor V, factor VIII, prothrombin fragments 1 and 2, tissue factor, von Willebrand factor, and protein C.
• Measurements were taken at rest and after 15, 30, and 60 minutes of standing.

Main Results:

• 30 minutes of standing decreased plasma volume by 12% and increased plasma proteins by 13%.
• Fibrinogen, factor V, and factor VIII activities increased significantly, as did prothrombin fragments 1 and 2.
• Endothelial activation markers (tissue factor, von Willebrand factor) rose, while protein C levels decreased.

Conclusions:

• A novel physiological mechanism, "orthostatic procoagulation," is proposed.
• This phenomenon involves increased procoagulant activity and endothelial activation during standing.
• Orthostatic procoagulation may be relevant to the pathophysiology of stasis and venous thromboembolism.