Biomedical Engineering Reference
In-Depth Information
However, feeding tubes, medical monitoring devices, and other technologies now allow PVS patients to
survive.
Anyone who has studied the history of technology knows that technological change is always a Faustian
bargain: Technology giveth and technology taketh away, and not always in equal measure. A new technology
sometimes creates more than it destroys. Sometimes, it destroys more than it creates. But it is never one-sided.
Neil Postman (8 March 1931-5 October 2003), educator, media theorist and cultural critic
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Postman's caution about the dichotomous, even bifurcated, nature of technology is especially relevant
to bioethics. The good stuff is readily apparent to both professionals and patients. A visit to the local
general practitioner's office, let alone a health clinic or hospital, provides evidence of the rapid pace at
which biomedical engineers have added to the practice of health care. Blood oxygen level readings can
be taken by devices that are completely noninvasive (light penetration). At the ophthalmologist's office,
glaucoma tests are on the ready and lasers can be used to reduce eye pressure. Epoxies and composites
used by the dentist to repair and to preserve teeth that would have been lost a decade ago are a tribute
to advances in materials sciences.
The potentially bad stuff may not be so apparent, but it can be found. Information technologies and
networks that allow for timely and reliable health care have also introduced new threats to patients'
privacy. Misuse of new treatments is possible, especially if the new technologies are not accompanied
by adequate training and oversight. Unforeseen risks and complications are often only apparent after a
device is introduced into the general patient population.
Teachable
Moment:
Medical
Device
Risk
The convexo-concave (C-C) tilting disk heart valve (Figure 5.3), designed and manufactured
by Björk-Shiley, has received much attention as a case of failure of a medical device.
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Few
engineered products have undergone the scrutiny that has focused on the C-C valve, for good
reason. The C-C valve was designed as an improvement to a replacement valve approved in 1969.
Among the reasons for designing the new valve was to reduce the risk of thromboembolism. The
new valve received premarket approval in 1979. Unfortunately, the “improvement” to the design
was a factor in its calamitous failure. The design changes included repositioning the outlet-strut
weld and changing the angle of orientation of the outlet strut to the ring.
The first failure of the outlet strut occurred during the premarket approval process, followed by
other failures addressed during the company's quality assurance process. However, the underlying
cause of the failure was not identified. This was later found to be an unexpected load on the
outlet strut's tip. The increased loading was the result of the redesign aimed at reducing throm-
boembolism. Subsequently, in 1984, the design modifications to address these loadings essentially
returned the outlet strut in the valve to the original configuration. Monitoring was also upgraded,
with an examination of the potential failure site in each valve by scanning electron microscopy.
The loss of life appears to have been preventable had the design process included measures to
address possible risks from seemingly small changes.
