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The right side of the heart pulls oxygen-poor blood in from the head
and extremities, and pumps it out to the right and left lungs, where it
is enriched with oxygen. The left side of the heart pulls the oxygen-rich
blood in, and pumps it back out to the head and extremities through the
aorta. The aortic valve, positioned between the left ventricle chamber
and aorta, controls the blood f low from the left side of the heart. Because
of the continual stresses placed on this valve, it is one component of
the heart that suffers frequent failure. Heart valve replacements are
often performed when this valve can no longer function independently.
Replacement heart valves can be either mechanical (rigid) or flexible.
The former are most commonly used because they are durable and rarely
require additional surgical attention after being deployed. The patient
must, however, remain on constant anticoagulant drug therapy if such a
valve is in use. Flexible valves, on the other hand, more closely mimic
the action of a natural valve. Early flexible valves were made from treated
animal tissue, and while these valves offered freedom from lifelong dependency
on anticoagulants, they degraded over time and eventually needed to be
replaced. More recently, f lexible valves have been made from synthetic
materials. These valves have the potential to function like natural valves
but have the durability of mechanical valves. By optimizing the design
of these valves, it is hoped that they can become better understood and
more widely used.
The flow through the valve is shown at four times during
the cardiac cycle, as the valve changes from fully open to fully closed
To study the workings of flexible valves, researchers in the Computational
Bio-Fluid Mechanics Research Group at the University of Leeds School of
Mechanical Engineering have used a combination of an in-house code and
FIDAP. Their goal has been an analysis of the coupled motion of a flexible
heart valve with the periodic flow of blood through the valve. Because
a detailed analysis of several valve designs would require extensive building
and testing, the CFD approach was used to make the most efficient use
of time and money. In addition, the CFD results would be able to provide
a more thorough picture of the flow-field inside the valve than could
traditional experimental methods.
The valve consists of a channel with a flexible leaflet surface whose
position changes the opening of the channel from fully closed (diastole)
to fully open (systole), approximately 72 times a minute. An in-house
code was used to provide the periodic motion of the leaflet. For each
leaflet position, a boundary condition for the leaflet was fed into FIDAP,
where the moving boundary condition model was used. The FIDAP results
were fed back into the in-house code, where leaflet stresses and a new
leaflet position were computed. This process was repeated for several
cardiac cycles.
The model has enormous potential as a design tool for flexible heart
valves in the future. Plans are now underway to more tightly couple FIDAP
to the University of Leeds' in-house code calculations for this purpose.
For more information, visit: http://www.leva.leeds.ac.uk/cbfm/
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