Chapter 97: Diagnosis and Management of Diseases of the Peripheral Venous System
Which of the following is not characteristic of the venous system?
A. Low resting vascular tone
The answer is D. (Hurst’s The Heart, 14th Edition, Chap. 97) The lower extremity venous system includes the deep, superficial, and perforating veins, which work in concert to return blood to the heart. Unlike the arterial system, the venous system is low resistance (option B) and must overcome gravitational and hydrostatic pressure forces to achieve blood return to the heart. The venules and veins have very thin walls and low resting basal tone (option A), which allows for enormous distensibility (option C). Having thin, floppy vascular walls also means that veins tend to have very high compliances (option D). As such, large increases in blood volume are required to even slightly enhance the internal blood pressure, and small changes in hydrostatic forces, central pressure, and/or external forces result in changes of the vein diameter. Venous blood flow is reliant upon muscular leg contraction as well as bicuspid venous valves (option E) that open and close to prevent backflow. Together, muscular leg contraction and venous valves help to overcome hydrostatic forces within the vein itself.
Which of the following is not considered part of Virchow’s Triad of risk factors for venous thrombosis?
The answer is B. (Hurst’s The Heart, 14th Edition, Chap. 97) Venous thrombosis may occur as a result of the risks as identified in Virchow’s Triad: stasis (option A), endothelial injury (option C), and the hypercoagulable state (option D), or it may occur without any known risk factors (unprovoked venous thrombosis). Stasis, or interrupted blood flow, typically occurs due to prolonged immobility (eg, on a plane), hospitalization, and varicose veins. Endothelial injury increases the risk of venous thrombosis via the activation of the coagulation cascade and recruitment of inflammatory cytokines. Lastly, any hypercoagulable state that facilitates blood clotting (eg, obesity, pregnancy, cancer) will result in changes of the constitution of blood and predispose to venous thrombosis. Hemophilia (option B) is a disorder of impaired blood clotting, resulting in increased bleeding and easy bruising; it does not typically constitute a risk factor for venous thrombosis.