Biomedical Engineering Reference
In-Depth Information
8.4
ARTIFICIAL HEARTS
An artificial heart is an implantable device that replaces all of the pumping actions of a
natural heart. It is known as a totally artificial heart (TAH) and includes two pumping
chambers that replace both the right and left ventricles. The earliest devices, such as the
Liotta-Cooley and Jarvik-7 hearts, were driven by large air pumps through air lines, as
shown in Figure 8-11.
A successful replacement for the natural heart must meet a number of basic require-
ments. It must be sufficiently small for implantation but still capable of pumping the
required blood volume, which is typically between 5 and 10 L/min. It must not produce
hemolysis or result in the formation of thromboemboli, and its materials must withstand
long-term flexing.
Current pumps use either a flexible sac acted on by a mechanical pusher plate or a rigid
chamber divided by a flexible diaphragm separating the blood from either compressed air
or hydraulic fluid. The blood contacting surfaces of these devices are commonly made from
three types of materials, each with their own advantages and disadvantages: (1) smooth
polyurethane; (2) a texturized pseudoneointima-forming surface; and (3) surfaces coated
with biolized or natural tissue coatings (Jaron, 1990).
The choice of energy source is an ongoing design trade-off. It has long been known that
pumps using compressed air supplied from outside the body are the simplest to design and
control, and all of the early TAHs discussed in this chapter used this technique. However,
these are not ideal, as the necessary connecting tubes provide a path for infection and a
bulky external compressor restricts patient mobility.
Electrically driven pumps have many advantages for both TAHs and LVADs; therefore,
considerable effort has been expended into finding methods of supplying electrical power
to implanted pumps. At present, battery technology is not sufficiently advanced to supply
FIGURE 8-11
Pneumatically driven
artificial heart.
(a) Schematic
diagram of the heart.
(b) Drawing of the
pump console and
attachments to a
human patient.
