Prosthetic Venous Valve

Prosthetic Venous Valve

By Justin Martin The veins carry oxygen depleted blood back to the heart from the rest of the body. In the legs, the veins have to fight gravity to deliver the blood back. This is aided by the surrounding muscles when a person is walking or doing other activities. When a person stands still or sits, the pumping motion of the blood stops, and the blood tries to move backwards

The venous valves are in place to block this backwards motion, also called reflux. CVI is vein condition that affects about 5 percent of the US population. CVI is usually caused when there is higher than normal blood pressure in the veins of the legs. This increase in pressure can weaken the blood vessels and even damage the valves. When the valves are damaged, they will no longer close properly, which can lead to an excess of reflux in the veins.

This problem can lead to lower extremity discomfort, swelling of the affected areas and changes in the skin Most treatments focus on decreasing the patients symptoms, and no the actual underlying problems. There are both surgical and nonsurgical methods to treat CVI. Non-Surgical Treatments Compression Stockings: Elastic stockings that are meant to squeeze the veins and stop excess reflux. Patients may need to wear these compression stockings everyday for their entire life. Sclerotherapy: This procedure involves an injecting a chemical into the improper functioning veins. The chemical then destroys the veins and make the blood choose another path to take. The destroyed veins are then absorbed by the body. Antibiotics can be used to cure some of the skin problems due to CVI, but the underlying causes of CVI wont be cured. Avoiding sitting or standing for long periods of time, will help to pump the blood back to the heart and control some of the

backwards blood movement. Surgical Treatments Ablation: Like sclerotherapy, the vein is destroyed from the inside, but in ablation a catheter with an electrode is used instead of chemicals. Bypass: For extensive problems, surgeons will connect an artificial or transplant vein to a healthy vein and bypass the damaged area. This procedure is usually recommended in more serious cases. Valve Repair: In valve repair, the surgeons will generally shorten the flaps of the valves to improve the valves functioning. A sleeve is usually placed on the outside of the newly fixed valve. This helps to press the walls together to maintain normal valve functioning.

There are no commercially available artificially venous valves. This is largely due to high failure rates, and biocompatibility issues. Prosthetic venous valves are believed to be able to restore normal vein functioning as an alternative to other surgical procedures. The proposed artificial valve will be able to be implanted into the vein through a catheter. The valve is designed to mimic the natural venous valve, by allowing blood to flow naturally when its being pumped by contraction, and stopping blood

flow when there is an absence of contractions. The synthetic valve is comprised of two different parts, a solid frame and flexible leaflets. Solid Frame: Comprised of a circular base that was formed from photo-activated polymer resin. The solid frame also contains a flange support structures to hold the flexible leaflets. Flexible Leaflets: Made of a polymer called BioSpan. After templates for the leaflets were created, they were then cut to shape by scalpel.

Made to mimic the flaps of a normal valve, by completely closing the passageway to block blood from moving backwards. They are attached to the frame by connecting them to the flanges. To test the design of the valve, a model that was two times larger than the desired valve was created. The valve was placed into set up where the valve was tested in a flow loop, with water as the fluid. During the tests, a few problems arose in the design of the valves. When closed, the leaflets had an

undesirable sagging. The bases of the valves were susceptible to breaking where the flanges met the edge of the base. This was due to the bending stress caused by the fluid. The problems were corrected by adding a beveled edge and an extra shoulder like extension to the supporting flange.

After the design problems were all worked out in the 2x tests, the valves were tested at their desired size. For the tests, four valves with varying flange lengths (1.25,2.50,3.75 and 5.00mm), underwent a series of procedures in the same fashion as the 2x tests, with a blood substitute as the fluid. Also a test with no valve at all was used to simulate the conditions of CVI, in which the valve usually fails. The tests were meant to simulate four different body movements. The movements were, breathing while laying down, ankle flexion while laying down, standing breathing and standing ankle flexion. The two main parameters that were calculated for the valves were the Percent Reflux, or the amount of fluid that flows backwards through the valve, and Energy Retention, the amount of energy being

retained by the valve in the form of potential energy. These tests showed that the valves with the 2.50 and 3.75mm flanges were superior to the 1.25 and 5mm flange valves. In the future, the scientists hope to incorporate drug delivery reservoirs within the flanges themselves. The reservoirs would administer their drugs through channels made of rate controlling materials. Multiple reservoirs per flange would also make it possible to contain more than one drug at a time, being able to cure multiple symptoms at once. Finding a biocompatible material for the frame would also lessen the rejection rate of the synthetic valves. Creating a leaflet molding process, and finding a new way to attach the leaflets to the frames would shrink the valve to valve design variability. Making the frame out of a expandable material would also allow the

synthetic valves to be deployed into the affected veins via a catheter. Oberdier, Matt T., and Stanley E. Rittgers. "The Design, Development, and Evaluation of a Prototypic, Prosthetic Venous Valve." BioMedical Engineering OnLine 7.25 (2008). Print. www.vascularweb.org/patients/ NorthPoint/ Chronic_Venous_Insufficiency.html http://encyclopedia.farlex.com/ Venous+valves

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