Page 551 - Handbook of Biomechatronics

544 Graham Brooker

• Porting valve—A separate motor rotates the valve which opens and
closes to let the hydraulic fluid flow from one side of the artificial
heart to the other in turn.
• Artificial ventricles—When the fluid moves to the right, it
compresses the flexible membrane on the inner surface of the right
artificial ventricle (pump sac) and blood is pumped to the lungs via a
nonreturn valve. When the fluid moves to the left, a similar sac is
compressed and blood is pumped to the rest of the body via a separate
nonreturn valve.
3.2 Dynamic (Continuous Flow) Pumps

Most second-generation VADs were based on axial pump technology. This
was made possible by advances in pump design that minimized damage to
blood constituents, as well as surface treatments on the surfaces in contact
with the blood to minimize clotting. The primary advantages of these
designs was the higher pumping efficiency coupled with significant reduc-
tions in size and mass. A wide variety of different design configurations have
been developed by different parties to try to minimize damage to red blood
cells (hemolysis) and to maximize efficiency.
A good example of the genre is the Thoratec HeartMate II with a volume
of 124mL and a length of about 70mm as shown in Fig. 18. This size advan-
tage gives it the potential to help a larger range of patients with the end-stage

Fig. 18 Cross section through the axial pump for the Thoratec HeartMate II. (Based on
Cleveland_Clinic, 2008. Ventricular Assist Devices (VAD). http://my.clevelandclinic.org/
heart/disorders/heartfailure/lvad_devices.aspx (Retrieved September 2008).)