Biomedical Engineering Reference
In-Depth Information
FIGURE 8-48
Novel heart assist
device. (a) Graphic
showing the
combined
SMA-Peltier
actuator.
(b) Photograph of
actuator on a plastic
model of the heart.
(Yambe, Maruyama
et al., 2001),
reproduced with
permission
8.5.10.1 Shape Memory Alloy Driven VAD
An alternative to having an external pump is to retain the left ventricle as the pumping
chamber but to develop a method to assist the heart muscle to contract. The contractile
properties of SMA can be used to this effect. It can easily be heated quickly enough to
change state and apply the required force to the ventricle, but natural cooling is generally
much slower. A solution to this problem is to use an array of Peltier elements to both heat
and cool the SMA mechanism much more quickly (Yambe, Maruyama et al., 2001). A
model of the device is shown in Figure 8-48.
8.5.10.2 Pulsatile Rotary Pumps
Pulsatile rotary pumps operate by cyclically varying the rotation speed of a centrifu-
gal pump to impose a synthetic cardiac rhythm. To minimize increases in Reynolds's
shear stress during acceleration and deceleration, the impeller vanes are curved (Kun-
xi and Ying, 2008). Figure 8-49 shows a comparison between the flow lines of a cen-
trifugal pump with curved impeller vanes and a conventional one with straight vanes.
It can be seen that in the former the blood flow follows the curved vanes with mini-
mal impact or separation, which results in a lower Reynolds's shear stress and lower
hemolysis.
8.5.10.3 Sunshine Heart/C-Pulse
The C-pulse is a pliable, inflatable cuff that encircles the patient's aorta, as shown in
Figure 8-50. It inflates and deflates in time with the patient's heart to perform a function
known as counterpulsation, which enhances blood flow and reduces the workload of the
left ventricle.
When the heart is filling, the C-pulse inflates, pumping blood from the aorta into
circulation. Just before the left ventricle begins its contraction, the cuff deflates, increasing
the volume available in the aorta, decreasing the aortic pressure, and therefore decreasing
the heart workload.
Because there is no blood contact and the C-pulse is inserted with minimum trauma,
it is an effective and safe method to counteract the effects of moderate heart failure.
