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SILIGURI INSTITUTE OF TECHNOLOGY

Name:-Moina Ersad.B-Tech ,2 nd Year ,4 th Semester

Department of BiomedicalEngineering.Roll No.:-11931061009

Session:-2007-2008Guide Teacher:-Sujan K.Samanta

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Topic of Seminar:-

ARTIFICIAL HEARTVALVES

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HEART:-

Heart is a vital part of the humananatomy, as it functions as a pump tocirculate blood throughout the body .

It consists of four chambers , namely theright atrium ,the right ventricle ,the leftatrium and the left ventricle.

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By the pumpingaction of the heart,oxygenated blood iscirculated

throughout thebody, and thedeoxygenated bloodis circulated back to

the heart ,to regainthe oxygen that waslost.

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HEART VALVES:-

Heart valves are very important ,asthey prevent the backflow of blood.This ensures the proper direction of

blood flow throughout the circulatorysystem .Without these valves the heartwould have to work much harder topush blood to the adjacent chambers.

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HEART VALVE PROBLEMS:-

Heart valves are prone to disease andmalfunction ,and can be replaced byartificial heart valves .These complicationsand diseases of heart valves can preventthe proper flow of blood throughout thebody.They are of two types:-

Stenosis Incompetence

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STENOSIS :-A stenotic heart valveprevents the valve from opening fully,due to stiffened valve tissue .Hence thereis more work required to push bloodthrough the valve.

INCOMPETENCE :-Incompetent valvescause inefficient blood circulation bypermitting backflow of blood in the heart.

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Echocardiogram of aortic valve stenosis: calcified leavesarrowed

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TREATMENT OPTIONS

On a large scale, medication is the bestalternative ,although in some casesdefective valves have to be replaced by

prosthetic valve, in order to make thepatient lead a normal life. A lot ofresearch work is being done byscientists and engineers to design aheart valve that can withstand millionsif not billions of cardiac cycle.

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Original photo of a replaced heart valve

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TYPES OF PROSTHETIC HEARTVALVES

There are two main types of Prosthetic heartvalve designs:- Mechanical Bioprosthetic

The mechanical valves are excellent in terms ofdurability, but have a tendency to coagulateblood.

Bioprosthetic valves are less durable and mustbe replaced periodically.

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The operating principle of different types of prostheticheart valves

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MECHANICAL HEART VALVES

The first mechanical prosthetic heart valve wasimplanted in 1952. Over the years 30 different mechanical designs

have originated worldwide.

These valves have progressed from simple cagedball valves to modern bileaflet valves. They emphasize on producing more central flow

and reducing blood clots. The common types of mechanical prosthetic

heart valves are caged ball, tilting disc, bileafletvalve.

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Different types of mechanical heartvalves

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Caged ball design:-

The caged balldesign is one of theearly mechanicalheart valves.

They use a small ballthat is held in placeby a welded metal

cage. It limits theflow of fluids in asingle direction.

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But there are certain disadvantages of caged ball

designs. Caged ball designs completely block centralflow, therefore the blood requires more energyto flow around the central ball.

The ball causes damage to blood cells due tocollisions.

These damaged blood cells release clotting

ingredients. As a result, the patients are requiredto take lifelong prescriptions of anticoagulants.

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Tilting disc design:-

This new class of prosthetic valves wereintroduced in the mid 1960s.

They used a tilting disc, that better mimicthe natural patterns of blood flow.

The tilting disc valves have a polymer discheld in place by two welded struts. The disc floats between two struts in such

a way, as to close when the blood beginsto move backward, and then reopenswhen the blood begins to travel forward.

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A tilting disc heart valve

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There are certain advantages of tilting disc designover caged ball design:-

They provide improved central flow while stillpreventing backward flow.

They reduce mechanical damage to blood cells.

Hence there is a reduced chance of bloodclotting and infection.The main disadvantage of the tilting disc design

is:-There is a tendency of the outlet struts to fracture,

resulting from fatigue, due to repeated rammingof the struts by the disc.

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Bileaflet valve:-

In 1979 ,a new type of mechanical heartvalve was introduced, known as thebileaflet valve.

It consists of two semicircular carbon

leaflets that pivot on hinges. The carbon leaflet exhibit high strength

and excellent biocompatibility.

The leaflets swing open parallel to thedirection of blood flow. They constitute majority of the modern

valve designs.

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A bileaflet prosthetic valve

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Bileaflet valve replacement

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The main disadvantage of bileaflet valve is

that, they do not close completely, whichallows some backflow of blood. Sincebackflow is one of the properties ofdefective valves, so bileaflet valves arestill not the ideal valves.

The main advantage of these valves is that,they provide the closest approximation tocentral flow, normally achieved in anatural heart valve.

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Bioprosthetic heart valves

Bioprostheticvalves can bebroken intotwo groups:-

Human tissuevalves

Animal tissue

valves

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Human tissue valve:-

Human tissue valves fall into two

categories:-Homograft:-It is a valve that is

transplanted from a deceased personto a recipient. It suffers minimumproblems of valve rejection, andhence do not requireimmunosuppressive therapy .They

are more durable.Autograft:-They are taken from the

same patient they are implantedinto. The most common autograftprocedure is the Ross procedure,

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Animal tissue valves:-

The animal tissue valves are often referredto as heterograft or xenograft valves.These are the animal heart tissues whichare often recovered from animals at thetime of commercial processing.

The most commonly used animal tissuesare:

Porcine- valve tissue obtained from pig Bovine -pericardial tissue obtained from

cow.

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A porcine valve

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A Bovine valve

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Heart valve replacement

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Advantages of Bioprosthetic heartvalve over mechanical heart valve

The design of the bioprostheticheart valve is closer to the designof natural valve.

The bioprosthetic valves do notrequire long term anticoagulants. They have better haemodynamics.

They do not cause damage toblood cells They do not suffer from many of

the structural problems,experienced by the mechanical

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Conclusion:-

When one of the valves of the heart becomesinfected with disease, it can be replacedwith one of several different types ofprosthetic valves.

The prosthetic valves must meet certainstandards with regard to inertia, strength,elasticity and electrochemical properties.

The replacement valve must also be durableas the human body is a harsh place forforeign objects, which can corrode orbreakdown.

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References:-

Biomaterials by Sujata Bhatt www.clevelandclinic.org www.atsmedical.com www.wikipedia.org www.yeastinfectionadvisor.com

http://www.clevelandclinic.org/http://www.atsmedical.com/http://www.wikipedia.org/http://www.yeastinfectionadvisor.com/http://www.yeastinfectionadvisor.com/http://www.wikipedia.org/http://www.atsmedical.com/http://www.clevelandclinic.org/

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