Biomedical Engineering Reference
In-Depth Information
biological valves which did not require anticoagulants or human donors. Porcine
aortic valve isolations were successfully used in humans once a means of
sterilizing the tissue was found. Buffered formaldehyde was used initially with
short-term success, but these valves ultimately failed. It was not until Alain
Carpentier introduced the use of dilute solutions of glutaraldehyde in 1968 to
sterilize the tissue that
long-term implants fabricated from animal-derived
tissues became possible.
Today, the clinician has a variety of options to consider when a patient needs a
valve replaced. Table 5.1 contains an overview of the different classes of replace-
ment valves, an example of the most popular valve in that category, as well as a list
of the advantages and disadvantages of each class. Through the diligent efforts of
engineers and scientists working closely with surgeons, heart valve replacement
surgery has saved millions of lives worldwide. Given the marked improvement in
quality of life and longevity, despite the limitations of today's current valves, it is a
certainty that advances in heart valve technology will continue.
5.2 Mechanical valves
A mechanical heart valve is a good illustration of the problems of multivariate
design issues in heart valves. Mechanical heart valves typically consist of a
circular support attached to a fabric sewing cuff or ring, supporting either a
single or bileaflet valve. The mechanical requirements of the bileaflet valve
(Fig. 5.2) have to do mainly with wear and fatigue resistance. The leaflets are in
nearly constant motion and contact the support at the pivot and closure points,
and they are stressed at a relatively high frequency. They may also be a nidus for
thrombosis and subsequent septic colonization. The high shear in the pivots
causes localized damage to blood elements leading to a high propensity for
TM
5.2 Classical mechanical valves. Left, the Regent
mechanical heart valve, a
modern bileaflet pyrolytic carbon valve from St. Jude Medical. Right, the
Starr-Edwards
TM
ball-and-cage valve, the first commercial heart valve.
TM
(Regent
is a trademark of St. Jude Medical, Inc. Reprinted with permission
of St. Jude Medical
TM
TM
is a
trademark of Edwards Lifesciences Corporation. Reprinted with permission of
Edwards Lifesciences LLC, All Rights Reserved.)
, ß 2010 All Rights Reserved. Starr-Edwards
