A major problem that scientists and engineers have researched to fix is a diseased or dysfunctional heart valve. Prosthetic heart valves have been engineered in order to replace the valves. If a heart valve malfunctions, the entire circulatory system could be affected. When a valve is not working properly, it tends to allow some blood to flow backwards, which decreases the amount of oxygen that is delivered throughout the body with each heart beat. Another valve malfunction is known as a stenotic valve. When a valve is considered stenotic it is stiff and thus does not open fully which forces the heart to pump more to move the blood through the small opening.
There are two major types of prosthetic heart valves: mechanical heart valves and biological heart valves. A mechanical valve is synthetically made and generally is capable of lasting a lifetime because the materials are non-corrosive. Biological valves, on the other hand, are heart valves of human cadavers or certain animals. The biological valves must be sterilized properly for human implantation for the body to better accept the foreign substance. The available products that are being used to replaced dysfunctional valves vary from mechanical leaflet valves to porcine valves that come from pigs.
One particular valve consists of two leaflet, or flap-like, structures made of carbon that are in the shape of a circle. The circle is surrounded by a polyester fabric. Such a valve is used to replace an aortic or mitral valve. The patients of mechanical valves, however, usually must be able to tolerate anticoagulant drugs to prevent blood clotting on the synthetic valve. Another mechanical heart can be created with two half-discs covered by a fabric ring. The discs are made of graphite, tungsten, and carbon coating so that they will not corrode.
A biological valve can be made from part of a cow’s jugular vein that is sterilized. The vein is treated with preservatives to keep it both durable and flexible. The cow’s vein has three leaflets that open to allow the blood flow. Another biological valve can use a pig’s aortic valve that is treated with preservatives and sterilized. Some of the pig valves cannot be used in patients with high calcium metabolism, as the valve will deteriorate rather quickly. Some of the bovine, or cow, and porcine, or pig, valves are contained within a plastic stent which is attached to the walls of the heart; therefore the valve is a mixture of both mechanical and biological.
After looking at the majority of the prosthetic valves that are available today, it appears that it is better to choose a mechanical valve. In the implantation of a mechanical valve, the body is less likely to reject the valve, even though anticoagulants are generally needed. Mechanical valves can also last much longer than most biological valves.
http://www.fda.gov/hearthealth/treatments/medicaldevices/prostheticheartvalve.html
http://encarta.msn.com/encyclopedia_761572608_4/Heart.html#p67
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5 comments:
Is there any mechanical out there or any ideas for one that has three flaps, like the biological ones? Cause sometimes trying to the mimic nature and improving it is either easier or better to do.
this is a very good point. when mimicking a biologic function it is always good to think about why/how things evolved to be the way they are.
there is indeed research being done on valves with three flaps. you can find some information on these by searching "tri-leaflet valves".
here is the website for one that explains what the benefits of having three flaps is as well as a video: http://www.roscardioinvest.ru/eng/index.php?id_subpart=5
the only problem i have with the tri leaflet valve is that from what i've read, certain polymers make artificial devices more hospitable for certain infections, though if this is not an issue with the valve design, it seems rather solid.
Yes, but that can apply to all artificial devices, and there lies a problem with all of them, oh well, we're progressing.
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