VAD Pump Designs

VADs, or ventricular assist devices, are used when needed to aid the hardest-working parts of the heart - the ventricles. Most of these are continuously flowing, meaning they don't stop and start moving blood in a similar pattern to a functional heart. Continuous flow VADs haven't shown any life-threatening side effects related to the unnatural flow of blood, and they are easier to make. They are most often used in the right ventricle, the only left ventricular assist devices (in the US) being pulsatile, mimicing the heart's natural beating.

The motors in the continuous flow VADs contain magnets with coils around them. Electrical currents are sent through the coils at controlled levels to spin the magnet, which is connected to the rest of he assembly, which therefore moves blood. Continuous flow pumps use either axial or centrifugal pumps. Axial pumps have helix-shaped blades which spin to act much like a propeller on a boat, propelling the blood along the motor's axis, while cenrifugal pumps have rotors shaped to spin the blood toarwds the outer edges of the pump. All of the pumps certified for use in the US by the FDA use bearings to hold the rotor in place; however, there are pumps used in European countries that use magnetic or hydrodynamic forces to suspend the rotor. The benefit of these newer forms of suspension is that there is much less wear on the pump with the lack of bearings (less moving parts), and also less wear on the blood.

The design I think is the best is the axial pump with an electromagnetically suspended rotor. I feel that a centrifugal pump would be more stressful on the blood than an axial pump, and also less efficient; an axial pump pushes the blood in one direction, while the the centrifugal pump does this by spinning the blood around a lot first. Also, the electromagnetically suspended rotor seems a better choice simply due to the reduced wear on the device, making it more reliable.

http://en.wikipedia.org/wiki/Ventricular_assist_device