VWF and obstructive sleep apnea syndrome: Other factors shown to be elevated in OSA include fibrinogen, clotting factors VII (FVIIa) and XII (FXIIa), and Von Willebrand factor (VWF), all of which play a role in blood coagulation [29]. This shows that chronic inflammation contributes to one of the key factors in Virchow’s triad, i.e., blood hypercoagulation.