Heart disease is the principal cause of death in most
industrialised countries. In the U.S.A. for example, 2.3 million individuals
suffer from chronic heart failure, with an annual increase in numbers of 17%.
It is estimated that 17,000 to 35,000 of them per year will die from this
disease if they are not given either a heart transplant or an artificial heart.
Unfortunately, the numbers of heart donors cannot meet the demand for
transplantation, and, at present, the artificial heart is a prohibitively
expensive alternative.
The total artificial heart (TAH) intended for the total replacement of the
natural heart is still some years away from realisation. However, the
ventricular assist device (VAD) which is used temporarily to maintain an ailing
heart is available now, although only in restricted numbers due to difficulties
in processing the biocompatible materials used during manufacture.
Consequently, such devices are expensive, costing anywhere from
AUS$30,000 for the pump head to AUS$200,000 for a complete system.
In this study, the Australian designed $quot;Spiral Vortex$quot; VAD was used to
investigate fabrication techniques for use in the eventual cost-effective
manufacture of a pump head costing approximately AUS$4,000. A second
VAD originally designed at the Kolff Laboratory, University of Utah, U.S.A.
was also used for comparative evaluation. The hard-shell Spiral Vortex VAD
is intended to be used outside the body, while the soft-shell Kolff VAD has the
advantage of being implantable for long-term use. They were cast from
epoxy resin and vacuum formed from polyurethane, respectively. Several
units of each were fabricated, including 60 of the Kolff VAD, for use in vitro
and in vivo experiments. From these experiments it was found that both the
Spiral Vortex and Kolff VADs could be fabricated to quality controllable
standards. The Kolff VAD was used exclusively in chronic animal
experiments, and was able to sustain sheep and goats for periods of up to
five weeks. Furthermore, it became evident that techniques used in
fabrication of the Kolff VAD could be adopted for use in the mass production
of the Spiral Vortex VAD.
The two other areas investigated in this study were the prosthetic heart
valves and drive systems used for an artificial heart. A high percentage of
the cost of an artificial heart is accounted for by the inflow/outflow valves.
The trileaflet valve used in the Kolff VAD, which mimics the natural heart
valve, was fabricated using inexpensive vacuum-forming techniques. Quality
control was found to be adequate, with good flow characteristics which could
be maintained for several weeks in animal experiments. Both the Spiral
Vortex and Kolff VADs are pulsation pumps which require a pneumatic driver
unit. This driver is the single most expensive component in a VAD system,
costing upwards of AUS$150,000. The theoretical efficiency of a compact
hydromechanical drive unit was investigated using a test rig to simulate an
original design based primarily on proprietary components. Results obtained
so far indicate that the proposed driver can operate only under limited
conditions as a result of its severe reduction in size.
By adopting mass production techniques wherever possible in the fabrication
of the VAD (pump head) and valves, and by reducing the cost and size of the
driver unit, it may therefore be possible to produce a cost effective ventricular
assist device system.
| Identifer | oai:union.ndltd.org:ADTP/219529 |
| Date | January 1995 |
| Creators | Ranawake, Manoja, n/a |
| Publisher | University of Canberra. Industrial Design |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Manoja Ranawake |
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