Biomechanics of Artificial Heart Valves

Today Cardiac surgery has advanced tremendously to enable repair of all cogenital heart defects, replacement of damaged hear valves and bypassing of coronary blocks.

• About 1 in 100o babies is born with deformed heart and 1/3 of them died in infancy.
• The imperfect functioning of the heart valve is due to various defects like hole  in the heart , arterial septal defects and ventricular septal defects.
• when the major vessels of the heart are wrongly  connected, then there is mixing of pure and impure blood.

Normal heart valve

Prosthetic valves:- 

• These are made from high grade plastic and metal.
• they need life long coagulating agent blood thinning agent. 
• the average durability of these valves is about 8 to 10 years.

Tissue valves:-

• They may be neither homograft or heterograft.
• homograft valves are taken from human beings.
• heterograft valves are taken from animals.
• Here blood thinning s not necessary.
• The average durability of these valve is smaller than the prosthetic valves.

Artificial pig valve

•   Heart valves prevent the backflow of blood, which ensuresthe proper direction of blood flow through the circulatory system. Without these valves, the heart would have to work much harder to push blood into adjacent chambers. The heart is composed of 4 valves

1. The Tricuspid valve is between the right atrium and right ventricle.
2.  The Pulmonary valve is between the right ventricle and the pulmonary artery.
3.  The Aortic valve is between ventricle and the aorta .
4.  The Mitral valve is between the left atrium and left ventricle. It opens and closes to control
   blood flowing into the left side of the heart.

Requirements for the design of artificial heart valves:-

• When the artificial heart valve is in contact with the blood , there would not be any hemolysis or blood clots.
• The valve material must be tough enough to withstand the heart beat rate thrugh out the life of the patient.
•  It should be designed small, light, reliable and efficient enough to enable it to be inserted surgically into the heart.

  

  Aortic valve

Mechanical Heart Valve:-

• Prosthetic Heart Valves are fabricated of different biomaterials. 
• Biomaterials are designed to fit the peculiar requirements of blood flow through the specific chambersof the heart, with emphasis on producing more central flow and reducing blood clots. 
• Some of these biomaterials are alumina, titanium, carbon, polyester, polyurethane...
• The mechanical properties of these biomaterials involve how a material responds to the application of a force. 
• The three fundamental types of forces that can be applied are stretching (tension), bending, or twisting. 
• Materials respond to the forces by deforming (change in shape). 
• An elastic response is reversible, while an inelastic response is irreversible. In the elastic region, an elastic modulus relates the relative deformation a material undergoes to the stress that is applied. 
• The transition between elastic deformation and failure occurs at the yield point (or stress) of the material. In designing a component with the material, an inelastic response is considered failure. 



Leaflet valve

• Failure can be plastic deformation or ductile failure. It can also be breaking, including brittle failure or fracture.

• Mitral Valve Replacement Valve replacement is done when valve repair is not possible.Artificial Heart valve is the last solution for people with a damage heart valve caused by any disease as regurgitation.In valve replacement surgery, an artificial prosthetic valve replaces the damaged mitral valve. The two types of artificial valves are mechanical and tissue. Mechanical valves, which are made of biomaterials,

  

  artificial mitral valve

  
  may last a long time. However the patient with a mechanical valve must use an anticoagulant medication such as warfarin (Panwarfin) for the rest of life to prevent blood clots from forming on the valve. If a blood clot forms on the valve, the valve won’t work properly. If a clot escapes the valve, it could lodge in an artery to the brain, blocking blood flow to the brain and causing a stroke. Tissue valves are made of biological tissue such as a pig’s valve. These kinds of valves are called bioprostheses. These may wear out over time and may need to be replaced in another operation. However the tissue valve can avoid use of long-term anticoagulation medication. Mitral valve repair or replacement involves open-heart surgery. Through an incision in the breastbone (sternum), the heart is exposed and connected to a heart-lung machine that assumes the breathing and blood circulation during the procedure. The surgeon then replaces or repairs the valve. After the operation, which lasts several hours, the patient spends one or more days in an intensive care unit, where the general recovery is closely monitored.