Venous valves

Venous stasis is slowed blood flow in the deep veins of the legs resulting from damage to venous valves, vessel obstruction, prolonged periods of immobility, or increased blood viscosity. Conditions associated with venous stasis include major medical illness (e.g., heart failure, myocardial infarction), major surgery, paralysis (e.g., stroke, spinal cord injury), polycythemia vera, obesity, or varicose veins. 

Postthrombotic syndrome (a long-term complication of DVT caused by damage to venous valves) may produce chronic lower extremity swelling, pain, tenderness, skin discoloration, and ulceration. 

William Harvey [77] taught that the heart is the only pump that propels blood around the closed circulatory loop. Liebau [78], on the other hand, based on experiments with fluid mechanical models of his own design, concluded that blood could be propelled around the loop without the benefit of cardiac and venous valves. Liebau demonstrated with his simplest model, consisting of two tubes with different elastic properties, free of valves, making a closed water-filled loop, that periodic compression at an appropriate, fixed site caused steady net fluid flow around the loop, but could not explain the reason why this occurred. The explanation, developed in 1998 [57], was that Liebau worked with an asymmetric loop to which he provided energy by periodic compression at some site. This was termed impedance defined flow, in view of the nonuniform distribution of impedances around the loop. (Compression at a symmetric point, if any, generates no steady net flow, either experimentally or theoretically.)... 

The conduit characteristics of the venous system primarily depend on the anatomy of the system. Valves in the veins of the limbs are crucial for reducing the pressure in dependent parts of the body. Even small movements from skeletal muscle activity tend to compress the veins and move blood toward the heart. A competent valve then blocks back flow, thus reheving the pressure when the movement stops. Even a few steps can reduce the transmural venous pressure in the ankle from as much as 100 mmHg to about 20 mmHg. Without this mechanism, transcapillary movement of fluid into the extravascular spaces results in edema. Varicose (swollen) veins and peripheral pooling of blood can result from damage to the venous valves. During exercise, the rhythmic contraction of the skeletal muscles, in conjunction with venous... 

About 1 % of the adult population suffer from venous leg ulcers in the UK. The condition mainly affects the elderly, especially women, and is a result of a previous venous thrombosis or incompetent venous valve within the... 

Figure 8.1 (a) Backward flow of blood due to incompetent valves, (b) proper functioning of venous valves (no backflow), and (c) venous ulcer. 

The coronary sinus is bounded posteriorly by the Thebesian valve joining with the Eustacian ridge from the inferior vena cava to become the tendon of Todoro, anteriorly by the tricuspid annulus, and inferiorly by the inferior vena cava (Fig. 5.1). The coronary sinus typically courses posteriorly and paral-lelly to the mitral annulus. The diameter of the coronary sinus can be quite variable and commonly has a prominent Thebesian valve over its orifice. This venous valve is often fenestrated and can occasionally impede placonent of long sheaths deeply within the main body of the coronary sinus. Additionally, within the mid-body if the coronary sinus, venous valves are often present, the most prominent is the venous valve of Vieussens, located at the junction of the vestigial remnant of the vein of Marshall and the origin of the great cardiac... 

When venous valves are weakened and allow regurgitation of blood, there is an abrupt increase in venous pressure (Alguire and Mathes, 1997 Beebe-Dimmer et al., 2005 Hjelmstedt, 1968). The increased pressure and resulting venous hypertension are the primary cause of chronic venous insufficiency (CVI) (Belcaro et al., 1989 Browse, 1986 Browse and Bumand, 1982 Hjelmstedt, 1968). The continued prevalence of hypertension leads to dilation of the incompetent veins, resulting in varicose veins like those shown in Figure 20.12, the most conunon manifestation of CVI (Alguire and Mathes, 1997 Bhutia et al., 2008 McLafferty et al., 2007). If left untreated, CVI can cause dramatic cosmetic changes in skin, lower limb pain, edema, deep vein thrombosis, and ulcers (Adhikari et al., 2000 McLafferty et al., 2007 Robertson et al., 2008 Schoonover et al., 2009 Tran and Meissner, 2002 Van Den Bos and... 

Fig. 4.31a-d. Venous valves. a,c Schematic drawings and correlative b,d long-axis 12-5 MHz US images over a peripheral vein illustrate the hemodynamic effects of a valve on venous blood flow. a,b During contraction of calf muscles (white arrows), the cusps (arrowheads) of the valve open, allowing blood (blue arrows) to flow toward the heart. c,d Once the muscle action has ceased, flow tends to reverse, closing the cusps of the valve. Closure of the valve impedes blood to direct it backward... 

S.J. Munger, J.D. Kanady, A.M. Simon, Absence of venous valves in mice lacking Connexin37, Dev Biol 373 (2013) 338-348. 

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