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ARTIFICIAL HEART A PROMISING APPROACH IN ARTIFICIAL ORGANS
Liliana Agostinho, 65109 and Joana Paulo, 72455
Master in Biomedical Engineering, 4th
year, 2nd
semester 2012
ABSTRACT
The emerging need of finding solutions on the medicine field appeals for high
technology intervention. The artificial organs’ development makes use of that
technology, not only using biomechanical techniques but also, and more recently,
cellular and tissue engineering allied to nanotechnology, to improve biocompability.
This paper makes an overview about what has been done in the field and focus the
particular case of the heart as an artificial organ, the different equipment and a future
perspective.
I. INTRODUCTION
One of the greatest advancements in the
world of medicine has been the ability to
create artificial organs that are able to restore
the proper function of a patient’s body. By
definition, an artificial organ is “a man – made
device that is implanted into the human body to
replace one or many functions of a natural
organ, which usually are related to life support”.
The main reasons for developing these devices
include:
o Life support to prevent imminent death
while awaiting a transplant;
o Dramatic improvement of the patient's
ability for self – care;
o Improvement of the patient's ability to
interact socially;
o Esthetic restoration after cancer surgery or
accident. [1,2]
The first case is the most critical and the one
that provides greater challenges for medical
and engineer community. Nowadays, the
average life expectancy is high due to better
healthcare, fact coupled with shortage of
organ donors, so organ assistance and
substitution devices will play a larger role in
managing patients with end-stage disease by
providing a bridge to recovery or a
transplant. For example, in the U.S. alone, the
annual need for organ replacement therapies
increases by about 10 percent each year.
The first approaches to artificial organs
only used synthetic components; however,
we can now talk in “biohybrid” organs, which
combine synthetic and biologic components,
often incorporating multiple technologies
involving sensors, new biomaterials, and
innovative delivery systems. [3]
The history of artificial organs started in
1885, when Frey & Gruber build and use the
first artificial heart–lung apparatus for organ
perfusion studies. Their device relies on a
thin film of blood and included heating and
cooling chambers, manometers, and
sampling outlets, which permits monitoring
of temperature, pressure, and blood gases
during perfusion. [4] Since that time, little
steps were taken towards the current
variability available.
The most obvious example may be the
dialysis machine, which although it implies a
continuous power supply, it completely
replaces the kidney’s function. There are
already other artificial options for the brain,
ear, eye, heart, limbs, liver, lungs, pancreas,
bladder, ovaries, uterus and trachea.
There’s a huge expectation that artificial
organs would be superior to ordinary donor
organs in several ways. They can be made to
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
2
order more quickly than a donor organ can
often be found; in a regenerative medicine
domain, it’s possible to construct an organ
being grown from a patient's own cells, so
there’s no need for immunosuppressant
drugs to prevent rejection.
II. STATE OF THE ART
The development of an artificial
implantable pancreas for treatment of diabetes
occurs since 1998 and is based on three
fundamental components: a blood glucose
monitor, an insulin pump and a control system.
The goals of this device are the prevention or
delay of chronic complications of diabetes, as
well as less patient inconvenience and
discomfort than with multiple glucose self-
tests and insulin injection. [5] The glucose
sensor consists on an immobilized enzyme and
an interface to an electrochemical transducer.
The main problem to overcome is the
progressive loss of function and lack of
reliability of the sensor, caused by tissue
reactions, such as inflammation, fibrosis and
loss of vasculature, harming time precision. [6]
Now there are two available models for
glucose sensors, MiniMed CGMS and
GlucoWatch. [7] The pump itself is placed
internally and injects continuously insulin on
peritoneal cavity.
According to a CNN publication (March
2012), this device is currently on a trial phase
and getting good results. [8]
Another type of approach is the
bioengineering one. A tissue containing islets
of Langerhans is implanted, which would
secrete the amount of insulin, amylin and
glucanon needed and deficient because of the
islets and beta cells destroyed by the disease.
They can be cells collected from animals or
designed from stem cells, and they are
encapsulated to block the immune response
and eliminate the requirement of
immunosuppressive drugs. [9]
Microencapsulation techniques are being
improved for providing an effective long-term
treatment or cure of type 1 diabetes. [10, 11]
Figure 1: The Bioartificial Pancreas using Islet Sheet technology.
On July 2011, in Sweden, an artificial
trachea, fully synthetic, tissue – engineered,
was successfully transplanted into a late –
stage tracheal cancer patient. The organ was
created entirely in the lab, using a scaffold
built out of a porous polymer, and tissue
grown from the patient's own stem cells
inside a bioreactor designed to protect the
organ and promote cell growth. [12]
Figure 2: Artificial trachea after two days of cell growth, just
before being implanted into the patient.
The first artificial organ for substituting
liver function was the Extracorporeal Liver
Assist Device (ELAD®), a bedside system that
treats blood plasma, metabolizing toxins and
synthesizing proteins just like a real liver
does. This device is used to extend patients’
lives until a liver transplant becomes
available, and it’s being explored if it can
relieve the burden on the patient’s liver
enough so that it can regenerate itself. [13]
On October 2006, it was noticed the world’s
first bioartificial liver has been grown from
stem cells by British scientists. The result liver
was the size of a coin but the same technique
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
3
can be employed to grow full-size livers.
Fifteen years from that time, it was predicted
these livers can be implanted into patients. [14,
15]
HepaLife, a company in Boston, announced
on 2008 the latest positive results of tests of its
PICM-19 cells inside the bioreactor that would,
if it becomes a real product, function as an
external liver. This device reduces levels of
toxic ammonia by 75% in fewer than 24 hours. [16]
Figure 3: HepaLife’s device structure.
III. HEART
11.. AAnnaattoommyy aanndd PPhhyyssiioollooggyy
The heart is a muscular organ, located on
the chest, which pumps the blood
continuously around the body through the
cardiac cycle. Its mass is between 250 and
350 grams and it is about the size of a fist. It
is surrounded by the lungs and protected by
the ribs and sternum. It’s constituted by a
contractile mass, called the myocardium,
coated inside by a thin membrane, the
endocardium, and outside by a double –
walled sac, the pericardium.
It is divided by the interatrioventricular
septum in two functionally separate and
anatomically distinct units, right and left: on
the first, only circulates venous blood returned
from the peripheral organs; on the second
circulates arterial blood, arriving from the
lungs, where it has been oxygenated.
Each half can be then cloven in two
chambers, the atrium and the ventricle. The
ventricles are separated from the atria by
atrioventricular (AV) holes, where are placed
valves that avoid blood reflux. There are the
mitral valve and tricuspid valve, on the left
and right side, respectively. These are
included on the blood pathway through the
heart, together with the aortic and pulmonary
valves.
Figure 4: Anterior view of the human heart.
The cardiac cycle has two phases: systemic
circulation, which begins at a contraction of
the left ventricle, pumping the blood out to the
body through the aorta, and ends when it
returns to the heart (right atrium) via superior
and inferior vena cava; pulmonary circulation,
starting on the right ventricle, then the blood
flows to the lungs where many gas exchange
occurs, and it arrives through the pulmonary
veins to the heart again (left atrium).
22.. PPaatthhoollooggyy
For the heart to fulfill its demanding task,
apart from a proper blood supply, it needs a
good functioning of the heart muscle. The
cardiac insufficiency (weakness of the heart
muscle) designates a disease in which the
heart muscle is weakened to such an extent
that it is no longer capable of pumping the
blood sufficiently powerful or adequately fast
through the blood vessels. In such a case, part
of the blood accumulates upstream of the
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
4
heart, and we refer to it as a cardiac
insufficiency or a heart weakness. The cause
for a cardiac insufficiency is to be found in an
acute or gradual injury of the heart muscle due
to, among others:
• cardiovascular disease;
• heart attack;
• high blood pressure;
• heart diseases that directly attack the
heart muscle or the cardiac valves.
If the symptoms occur all of a sudden and
rather quickly, we refer to it as an acute
cardiac insufficiency. The chronic cardiac
insufficiency, in contrast, often develops
slowly and gradually, in most cases over a
period of several months or years. [17]
The weak heart muscle causes the patients
to feel symptoms that result from the fact
that the heart is no longer capable of
providing a sufficient blood supply for the
body and blood accumulates upstream of the
heart. Early symptoms of a cardiac
insufficiency are:
• reduced physical fitness;
• shortness of breath during hard physical
activity, when climbing stairs or
exercising;
• water retention (edema) in ankles and
back of the foot.
In the further course of the disease the water
retention may also affect other organs
eventually resulting in a weight gain. In an
advanced case of cardiac insufficiency the
patient will feel breathlessness also under
slight physical stress or even when at rest.
We distinguish between different stages of
cardiac insufficiency: [9]
• low-level with the symptoms occurring
only under hardest physical stress;
• high-level with symptoms such as
shortness of breath already in a state of
rest;
The necessary treatment is determined by
the stage of the cardiac insufficiency.
IV. EVOLUTION: FROM VALVES TO TOTAL
ARTIFICIAL HEART
11.. HHiissttoorryy aanndd AAddvvaanncceess ooff AArrttiiffiicciiaall HHeeaarrtt VVaallvveess
The first mechanical prosthetic heart valve
was implanted in 1952. Over the years, 30
different mechanical designs have originated
worldwide. These valves have progressed from
simple caged ball valves, to modern bileaflet
valves.
The caged ball design is one of the early
mechanical heart valves that use a small ball
that is held in place by a welded metal cage.
The ball in cage design was modeled after ball
valves used in industry to avoid backflow.
Natural heart valves allow blood to flow
straight through the center of the valve. This
property is known as central flow, which keeps
the amount of work done by the heart to a
minimum. With non-central flow, the heart
must work harder to compensate for the
momentum lost due to the change of direction
of the fluid. Caged-ball valves completely block
central flow; therefore the blood requires more
energy to flow around the central ball. In
addition, the ball may cause damage to blood
cells due to collision. Damaged blood cells
release blood-clotting ingredients; hence the
patients are required to take lifelong
prescriptions of anticoagulants. [18]
For a decade and a half, the caged ball valve
was the best artificial valve design. In the mid-
1960s, new classes of prosthetic valves were
designed that used a tilting disc to better
mimic the natural patterns of blood flow. The
tilting- disc valves have a polymer disc held in
place by two welded struts. The disc floats
between the two struts in such a way, as to
close when the blood begins to travel
backward and then reopens when blood begins
to travel forward again. The tilting-disc valves
are vastly superior to the ball-cage design. The
titling-disc valves open at an angle of 60° and
close shut completely at a rate of 70
times/minute. This tilting pattern provides
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
5
improved central flow while still preventing
backflow. The tilting-disc valves reduce
mechanical damage to blood cells. This
improved flow pattern reduced blood clotting
and infection. However, the only problem with
this design was its tendency for the outlet
struts to fracture as a result of fatigue from the
repeated ramming of the struts by the disc.
Figure 5: Caged ball valves. (a) Hufnagel–Lucite valve, (b) Starr–Edwards, (c) Smeloff–Cutter, (d) McGovern–Cronie, (e) DeBakey–Surgitool and (f) Cross–Jones.
Bileaflet valves were introduced in 1979.
The leaflets swing open completely, parallel
to the direction of the blood flow. The
bileaflet valves were not ideal valves. The
bileaflet valve constitutes the majority of
modern valve designs. These valves are
distinguished mainly for providing the
closest approximation to central flow
achieved in a natural heart valve. [19]
Figure 6: Bileaflet valve models. (a) St. Jude Medical, (b) Carbomedics and (c) Duramedics.
Biological tissue valves are made from
porcine aortic valves or fabricated using
bovine pericardial tissue and suitably treated
with gluteraldehyde to preserve them and to
remove antigenic proteins. Clinical
experiences with different tissue valve
designs have increasingly indicated time-
dependent (5 to 7 year) structural changes
such as calcification and leaflet wear, leading
to valve failure. Therefore tissue valves are
rarely used in children and young adults at
present. [18, 19] On the other hand, mechanical
valves made with high strength
biocompatible material are durable and have
long-term functional capability. However,
mechanical valves are subject to thrombus
deposition and subsequent complications
resulting from emboli, and so patients with
implanted mechanical valves need to be on
long-term anticoagulant therapy. Currently,
mechanical valves are preferred except in
elderly patients or those who cannot be put
under anticoagulant therapy, like women
who may still wish to bear children, or
hemolytic patients.
22.. MMeecchhaanniiccaall HHeeaarrtt VVaallvvee
Prosthetic Heart Valves are fabricated of
different biomaterials. Biomaterials are
designed to fit the peculiar requirements of
blood flow through the specific chambers of
the heart, with emphasis on producing more
central flow and reducing blood clots. Some
of these biomaterials are alumina, titanium,
carbon, polyester and polyurethane.
The mechanical properties of these
biomaterials involve how a material responds
to the application of a force. The three
fundamental types of forces that can be
applied are stretching (tension), bending, or
twisting. Materials respond to the forces by
deforming (changing shape). An elastic
response is reversible, while an inelastic
response is irreversible. In the elastic region,
an elastic modulus relates the relative
deformation a material undergoes to the
stress that is applied. The transition between
elastic deformation and failure occurs at the
yield point (or stress) of the material. In
designing a component with the material, an
inelastic response is considered failure.
Failure can be plastic deformation or ductile
576 Kalyani Nair et al
Figure 1. Caged ball valves. (a) Hufnagel–Lucite valve, (b) Starr–Edwards, (c) Smeloff–Cutter,(d) McGovern–Cronie, (e) DeBakey–Surgitool and (f) Cross–Jones.
2. History of mechanical valve
The pioneering efforts of Dr. Charles Hufnagel, who made the first successful placement of a
totally mechanical valvular prosthesis, started the era of artificial heart valves [1,2]*. Hufnagel
achieved this feat in 1952, by inserting a Plexiglas cage containing a ball occluder into the
descending thoracic aorta. The first implant of a mitral valve replacement in its anatomic
position took place in 1960, when the Starr-Edwards prosthesis was put the clinical use [3].
A number of similar caged ball designs appeared subsequently; like the Magovern–Cromie,
DeBakey–Surgitool, Smeloff–Cutter prostheses (see figure 1).
Even though caged ball valves have proven to be durable, their centrally occluding design
results in a larger pressure drop across the valve and higher turbulent stresses, distal to the
valve. Their relatively large profile increases the possibility of interference with anatomical
structures after implantation. This led to the development of low-profile caged disc valves in
the mid-1960s. The Cross–Jones, Kay–Shiley and Beall caged-disc designs were introduced
during 1965 to 1967 [4]. These valves were used exclusively in the atrio-ventricular position.
However, because of high complication rates, this model soon fell into disuse.
The next significant development was the introduction of tilting disc valves by Bjork–
Shiley in 1967 [4]. The design concept of this valve involves a free-floating disc, which in
the open position tilts to an angle depending on the design of the disc-retaining struts. In
the open position it acts like an aerofoil, with the blood flowing over and around it, thus
minimising the flow disturbance. The original Bjork–Shiley prosthesis employed a Delrin
*References in this paper are not in journal format
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
6
failure. It can also be breaking, including
brittle failure or fracture. Mechanical
properties of a material in the range of elastic
behavior include its elastic modulus under
tension and shear stresses, its Poisson’s ratio,
its resilience, and its flexural modulus. The
transition to failure is denoted by the yield
stress or breaking strength of the material.
During the last fifty years of development, a
set of material requirements for valves have
evolved which can be summarized as [18]
below:
Cause minimal trauma to blood elements
and the endothelial tissue of the
cardiovascular structure surrounding the
valve;
Show good resistance to mechanical and
structural wear;
Minimize chances for platelet and
thrombus deposition;
Be non-degradable in the physiological
environment;
Neither absorb blood constituents nor
release foreign substances into the blood;
Have good processibility (especially
suitable for sterilization of the device by
appropriate means) and take good surface
finish.
Problems that interfere with the
successful performance of valves can be
grouped as below:
Degradation of valve components;
Structural failure;
Clinical complications associated with the
valve.
Clinically, valve failure has been
considered to be present if any of the
following events require reoperation and/or
cause death:
Anticoagulant-related hemorrhage (ACH);
Prosthetic valve occlusion (thrombosis or
tissue growth);
Thromboembolism;
Prosthetic valve endocarditis (PVE);
Hemodynamic prosthetic dysfunction,
including structural failure of prosthetic
components (strut failure, poppet escape,
ball variance);
Reoperation for any other reason (e.g.:
hemolysis, noise, and incidental).
The performance of mechanical valves is
in several ways related to valve design and
structural mechanics. The design
configuration affects the load distribution
and dynamics of the valve components,
which in conjunction with the material
properties determine the durability and
successful performance of the valve. The flow
engendered by the geometry of the
components determines the extent of flow
separation and high shear regions. The
hinges in the bileaflet and tilting disc valves
can produce regions of flow stagnation,
which may cause localized thrombosis, which
may in turn restrict occluder movement. [18,
19]
Biochemical degradation and mechanical
wear is often inter-related, since degradation
accelerates material removal from surface
due to wear, which in turn accelerates the
rate of the biochemical reaction by
continually exposing new surface to the
corroding media. The use of large surface
areas of exposed metal in valves is often
quoted as leading to thromboembolic
complications. A cloth covering on the metal
can sharply reduce these complications, but
other problems associated with fabric wear
or uncontrollable tissue proliferation that
restricts flow can arise. The degradation of
the silicon-rubber balls used in ball valves
provides a good development in mechanical
heart valve prosthesis example of
deterioration caused by biochemical
incompatibility and also leads to mechanical
failure.
Under the conditions used, namely high
flow rate, all of the materials are reasonably
non-thrombogenic. Very small surface cracks
have been demonstrated to initiate thrombus
formation, presumably due to a small volume
of stagnant flow. In spite of desirable
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
7
characteristics of the biomaterials used in the
heart valves prosthesis, problems of
thromboembolic complications continue to
occur at the rate of 1 to 3% per patient year
in these valves. The mechanical stresses
induced by the flow of blood across the valve
prosthesis have been linked to blood damage
and activation of formed elements (red blood
cells, white blood cells and platelets)
resulting in the deposition of thrombi in
regions of relative stasis in the vicinity of the
valve. [20]
The pressure distribution on the leaflets,
and impact forces between the leaflets and
guiding struts are also being experimentally
measured in order to understand the causes
of strut failure. The flow through the
clearance between the leaflet and the housing
at the instant of the valve closure and in the
fully closed position, and the resulting wall
shear stresses within the clearance are also
suggested as being responsible for clinically
significant hemolysis and thrombus
initiation. Further improvements in the
design of the valves based on the closing
dynamics as well as improvements in
material may result in minimizing
thromboembolic complications as well as
occasional structural failure with implanted
mechanical valves. [18-20]
33.. HHeeaarrtt CClloonniinngg
Existing methods of treatment are not
quite effective in repairing damaged heart
muscle in end-stage cardiovascular diseases.
New research suggests that stem cells can
regenerate into heart cells. Nandini
Patwardhan traces the significance of stem
cells in the cardiovascular segment. [13]
Stem cells can be used for any kind of
myocardial infarction (heart attack) like
acute myocardial infarction, chronic
myocardial infarction and congestive heart
failure. However, it is advisable to treat
patients with myocardial infraction at the
earliest, preferably within 20-25 days of
heart attack. “Stem cells help reduce cardiac
infarction and improve ejection fraction,”
reveals Totey. Also, stem cells can be injected
in patients with cardiac myopathy. “Cardiac
myopathy is a condition, in which, the heart
muscle gets inefficient. And therefore, the
pumping efficiency of the heart or ejection
fraction as it is called, decreases to the extent
that the patient starts to feel breathless and
unable to function and heart failure occurs,”
explains Dr Ashok Seth, Chairman and Chief
Cardiologist, Max Heart & Vascular Institute,
Delhi. [21]
After a person gets a heart attack, the
cardiomyocites can die within 20 minutes
due to the occlusion of the artery. Once dead,
the heart starts remodeling itself to maintain
the normal cardiac output and to meet the
demands of the body. Stem cells, if injected at
the appropriate time, help in regenerating
the damaged muscles and healing the scarred
tissue, thereby, bringing the cardiac functions
to almost normal without causing
remodeling.
Figure 7: Heart steam cells were injected in the "skeleton" of a
heart and placed it in an incubator. Days later, the new heart
started beating.
Studies undertaken in small and big
animals have proved that when injected with
stem cells, they have the ability to home in on
the diseased muscles and then change
lineage. But the question that arises is, how
do these cells multiply into the desired
muscle cells? “For instance, when we inject
stem cells into the heart, they know exactly
where they have to home in, based on the
chemo attraction. The dead muscle gives out
certain chemocytes, which attract stem cells
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
8
to go there and convert into that lineage,”
states Shah. “Before we ventured on to
humans, we have seen this being proved
through various experiments on small and
big animals,” he adds. Unfortunately, there is
no way to control multiplying stem cells into
different non-desirable tissues. “However,
there is not a single report which shows that
stem cells, after injection into particular
organ, have developed into undesirable
tissue or cells. That shows that stem cells
injection are quite safe,” reveals Totey. [21]
The process of injecting stem cells is not a
very long drawn process. “We inject stem
cells by the intra-coronary method. This
means, we inject them into the coronary
artery—the culprit artery of the patient. The
muscle which is subtended by this artery,
which has been blocked, is our area of
interest,” discloses Shah.
A guiding catheter is put into the coronary
artery. Then a wire is sent over it into the
culprit artery. A balloon is sent on the wire.
Once inside the artery, the balloon is inflated
to stop the blood supply for a couple of
minutes. A lumen is inserted, through which a
million stem cells, cultivated from the bone
marrow of the patient, are injected in the
artery. The stem cells reach the target area,
where they have to home in. The balloon is
inflated till the stem cells are injected so that
blood does not flow during the process. “We
keep the balloon inflated for two to three
minutes, inject the stem cells and deflate the
balloon. Again after three to four minutes, we
repeat the procedure till all the stem cells are
injected,” explains Shah. “On an average we
inject 100 million stem cells. However, we
are doing it arbitrarily right now,” he adds.
44.. TToottaall AArrttiiffiicciiaall HHeeaarrtt
A total artificial heart (TAH) is a device
that replaces the two lower chambers of the
heart. These chambers are called ventricles
(VEN-trih-kuls). You may benefit from a TAH
if both of your ventricles don't work due to
end-stage heart failure. [22]
You may need a TAH for one of two reasons:
To keep you alive while you wait for a
heart transplant;
If you're not eligible for a heart transplant,
but you have end-stage heart failure in
both ventricles.
The TAH is attached to your heart's upper
chambers—the atria (AY-tree-uh). Between
the TAH and the atria are mechanical valves
that work like the heart's own valves. Valves
control the flow of blood in the heart. (For
more information, go to the Health Topics
How the Heart Works article.)
Currently, there are two types of TAH.
They're known by their brand names: the
CardioWest and the AbioCor. The main
difference between these TAH’s is
CardioWest is connected to an outside power
source and AbioCor isn't.
CardioWest has tubes that, through holes
in the abdomen, run from inside the chest to
an outside power source.
Figure 8: A - shows the normal structure and location of the
heart. B - shows a CardioWest TAH. Tubes exit the body and
connect to a machine that powers and controls how the
CardioWest TAH works.
AbioCor is completely contained inside the
chest. A battery powers this TAH. The battery
is charged through the skin with a special
magnetic charger.
Energy from the external charger reaches
the internal battery through an energy
transfer device called transcutaneous energy
transmission, or TET. [22]
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
9
An implanted TET device is connected to
the implanted battery. An external TET coil is
connected to the external charger. Also, an
implanted controller monitors and controls
the pumping speed of the heart.
Figure 9: A - shows the normal structure and location of the
heart. B - shows an AbioCor TAH and the internal devices that
control how it works.
Therefore, a TAH usually extends life for
months beyond what is expected with end-
stage heart failure. If you're waiting for a
heart transplant, a TAH can keep you alive
while you wait for a donor heart. It also can
improve your quality of life. However, a TAH
is a very complex device. It's challenging for
surgeons to implant, and it can cause
complications. [22]
Currently, TAHs are used only in a small
number of people. Researchers are working
to make even better TAHs that will allow
people to live longer and have fewer
complications.
V. CONCLUSION
Some devices - such as the left ventricular
assist device and bioartificial liver - will
provide assistance while new therapies
incorporating stem cells, gene therapy, or
engineered tissues are employed to repair or
replace the damaged organ. Until these new
therapies can be developed and tested,
medical devices will play a crucial role in
facilitating organ recovery and, perhaps,
organ salvage through natural repair
mechanisms. Where organ recovery is not
possible, artificial organs - when fully refined
- will provide a substitute for natural organs.
There has been considerable
improvement in the durability and functional
efficiency of mechanical heart valves. These
improvements have been by gradual
incremental improvements coupled with a
few revolutionary advances like the
introduction of tilting disc/bileaflet valves.
Despite all these improvements,
complications (though their rates are very
low) continue to be associated with their use.
All current models of mechanical heart valves
need anti coagulation therapy to minimize
the risk of thrombosis and embolism.
Management of anticoagulation levels and
bleeding are other concerns.
Recent trends in the choice of materials
indicate a preference towards soft occluder
materi- als. One team in Germany is working
towards bileaflet valves with soft occluders.
Medtronic– Hall also had announced that
they will be looking for a valve with soft
occluder in the near future. The advantages
of using soft occluder material are many.
They absorb the impact forces generated
during valve closure, there by reducing the
chance of suture dehiscence. The reduc- tion
in the impact forces also reduces the load
that needs to be transferred to the
surrounding tissues through the suture ring,
reducing the irritation caused by the
continuous movement at the cloth–metal
interface. Another improvement caused by
the soft occluder is the reduction in the
probability of occurrence of cavitation and
cavitation damage. This has been reason-
ably established by various studies
conducted on Chitra heart valve, which
showed that even at very high loading rates,
the chance for cavitation in valves with soft
occluders is minimum.
ARTIFICIAL HEART, A PROMISING APPROACH IN ARTIFICIAL ORGANS Liliana Agostinho, 65109 and Joana Paulo, 72455
10
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