Biomedical Engineering Reference
In-Depth Information
A 2 m long external air line feeds compressed air to the chamber where changes in
the pressure flex the diaphragm cyclically to drive blood flow. These air lines are attached
to the large compressor and control console, which regulates the pump stroke and dictates
the pumping rate.
After Clark's operation and not withstanding his less than satisfactory quality of
life posttransplant, the Jarvik-7 heart was implanted many times. The record for being
sustained by this artificial heart is held by William Schroeder, who was hooked to a
Jarvik-7 in 1985. He lived for 18 months with a far better quality of life, though he did
suffer strokes, sudden hemorrhages, and infections during his final days. A 1985 study of
15 patients with active infections from device implantation showed mortality rates as high
as 70%. Most infections developed from the site of the percutaneous tubes passing into
the body, though some arose from blood clots that developed from the internal surfaces
of the pump (Lemelson-MIT, 2002).
As materials improved, the survival rate improved, but after about 90 people had
received the Jarvik device the implantation of artificial hearts was banned for permanent
use in patients with heart failure because most of the recipients could not live more than
half a year and their quality of life was poor. However, for some time after the ban it was
still used as a BTT device.
Hiroaki Harasaki of the Cleveland Clinic developed two important improvements for
the artificial heart and other potential artificial organs. The first was a nonclotting surface
material that significantly reduced the risk of rejection of the organ by the patient's immune
system. The second development, which required the collaboration of many disciplines,
was an implantable power source that did not create tissue-damaging heat.
As the technical challenges were overcome, more companies started to manufacture
totally implantable artificial hearts. These companies include Thoratec, Medquest, Baxter
Novacor, Syncardia Systems, and AbioMed. To date, all of the problems have not been
solved, and researchers continue to work on designs for an artificial heart that could
provide a realistic, permanent option for survival of patients not considered suitable for
heart transplants.
8.4.1.3 Syncardia Systems/CardioWest
The CardioWest (now Syncardia) temporary total artificial heart (TAHt), shown in Fig-
ure 8-15, was developed from the Jarvik-7 by University of Arizona researchers and
approved for use in 2004. It is the first implantable artificial heart to be approved by the
U.S. Food and Drug Administration (FDA) and has also been approved by the Conformite
Europeenne (CE) (Europe) and Health Canada (NationMaster Encyclopedia, 2008).
The CardioWest heart is a pulsating biventricular device that is implanted into the
chest to replace the patient's left and right ventricles. Compared with the Jarvik-7, it is
very light, weighing only 160 g, but in other respects it is very similar to its predeces-
sor. It is lined with polyurethane and has a four-layer pneumatically driven diaphragm.
Four Medtronic-Hall mechanical valves ensure that blood flows correctly through the
device.
The pneumatic control system is set to fully eject all of the blood from each ventricle
with each beat. This is achieved by setting the ejection pressure of the right ventricle to
30 mmHg higher than the pressure in the pulmonary artery and that of the left ventricle
60 mmHg higher than systemic pressure, as shown in Figure 8-16. The ventricles are
adjusted to fill to between 50 and 60 ml to allow for some overhead during the fill phase.
This produces between 7 and 8 L/min while maintaining the correct Starling law pressure
