A BIOENGINEERING APPLICATION
B.AVINASH, V.RAVINDRA, B.ANIL KUMAR
B.TECH III/IV IT
Interest in development of mechanical cardiac support has grown out of the realization of
the enormous impact of heart failure-related mortality, the limited potential to provide cardiac
transplantation (approximately 2000 patients/year in the USA), and the long waiting period required,
even in appropriately selected patients. Both left ventricular assist devices (LVADs) and total
artificial hearts (TAHs) have been developed to assist in addressing these needs. This review focuses
on TAH development. Since that time, evolution of device design and manufacture, patient selection,
and ancillary therapies have occurred. Worldwide clinical application now spans 27 years and
includes experience with TAH implantation in 311 patients, with eight different pneumatically driven
devices implanted either as permanent devices (N = 5) or as temporary, bridging therapy to
transplantation (N = 306), with all but four implanted after 1984. Utah-developed TAHs represent the
largest source of this experience (N = 287). Infection rates have also decreased. Only one implanted
patient died of TAH mechanical failure (an early experience). Based on this evolving experience, use
of the TAH as a bridge to transplantation in selected patients who are not appropriate for an LVAD
has become a viable current therapeutic option.
A synthetic replacement for the heart remains one of the long-sought holy grails of
modern medicine. The obvious benefit of a functional artificial heart would be to lower the
need for heart transplants, because the demand for organs always greatly exceeds supply.
Although the heart is conceptually simple (basically a muscle that functions as a
pump), it embodies subtleties that defy straightforward emulation with synthetic materials
and power supplies. Consequences of these issues include severe foreign-body rejection and
external batteries that limit patient mobility. These complications limited the lifespan of early
human recipients to hours or days. The first bridging TAH was implanted in 1969, and the
first permanent device in 1982 with a patient survival of 112 days. In the earlier (Symbion
manufactured) TAH series (N = 204, 1985–1992), 42% of implanted patients and 59% of
transplanted patients were discharged alive from the hospital, and average support time was
24 days. In the current (Cardio West manufactured) series (N = 78, 1993–1996), 67% of
implanted patients and 94% of transplanted patients were discharged alive, and average
support time is 30 days. Of transplanted and discharged patients, 98% remain alive. With
improvements in device design and manufacture, as well as anticoagulant regimens, the
incidence of stroke with long-term deficits has decreased from 3 out of 7 in 1984-1985 to 1
out of 61 in 1988, with no permanent deficits since then.
DIFFER FROM OTHERS:
An artificial heart is also distinct from a CARDIOPULMONARY BYPASS
MACHINE (CPB), which is an external device used to provide the functions of both the
heart and lungs. CPBs are only used for a few hours at a time, most commonly during heart
PICTURE WHEN HEART IS BEING TRANSPLANTED
EAR LIER DESIGN ANALYSIS:
A precursor to the modern artificial heart pump was built by Bill Sewell using an
Erector set, assorted odds and ends, and dime store toys. The external pump successfully
bypassed the heart of a dog for more than an hour.
The first artificial heart implanted in a living being was placed in a dog at the
Cleveland Clinic in 1957; it survived about 90 minutes.
In 1964, the National Institutes of
Health started the Artificial Heart Program, with the goal of putting a man-made organ into a
human by the end of the decade.
MODERN ADVANCEMENTS IN DESIGN:
Recent studies tells us that fully implantable artificial heart will be ready for clinical trial
by 2011, and for alternative transplant in 2013. It was developed and will be manufactured by him,
Biomedical firm Carmat, and venture capital firm Truffle. The prototype uses electronic sensors and
is made from chemically treated animal tissues, called "biomaterials", or a “pseudo-skin” of
biosynthetic, microporous materials. Another US team with prototype called 2005 MagScrew Total
Artificial Heart, including Japan and South Korea researchers are racing to produce similar projects.
SAMPLE PICTURE OF RECENTLY DEVELOPED DESIGN
The heart valve acts as a check valve, opening and closing to control blood flow.
This cycle occurs about 40 million times per year or two billion in an average lifetime.
Natural valves can develop several problems, either the valve opening becomes narrow or
may not close completely. The first condition decreases the pumping efficiency and limits the
amount of blood pumped to the body. The second condition can reduce the amount of blood
to the rest of the body, as well as result in excess pressure in the lungs, also limiting their
efficiency. In the United States, more than 80,000 adults undergo surgical procedures to
repair or replace damaged heart valves every year.
Artificial heart valves consist of an orifice, through which blood flows, and a
mechanism that closes and opens the orifice. There are two types of artificial heart valves:
mechanical devices made from synthetic materials; and biological or tissue valves made from
animal or human tissue. In general, biological valves are used for patients who are over 65 or
cannot take anticoagulants. Mechanical valves are used for patients that have a mechanical
valve in another position, have had a stroke, require double valve replacement, and usually
are recommended for those under 40. These type of valves require the patient to take anti-
Mechanical valves can be further broken down into three types based on the
opening and closing mechanism. These mechanisms are: a reciprocating ball, a tilting disk, or
two semicircular hinged leaflets. The first type is based on a ball-in-cage design, which uses a
rubber ball that oscillates in a metal cage made from a cobalt-chromium alloy. When the
valve opens, blood flows through a primary orifice and a secondary orifice between the ball
and housing. About 200,000 of these have been implanted.
The tilting disk valve uses a circular disk retained by wire-like arms that project
into the orifice. When the disk opens, the primary orifice is separated into two unequal
orifices. About 360,000 of these valves have been implanted. The current design consists of
two semicircular leaflets connected to the orifice housing by a hinge mechanism. The leaflets
separate during opening, producing three flow areas in the center and on the sides. Over
600,000 bileaflet valves have been implanted.
HEART ASSIST DEVICES:
1) VENTRICULAR ASSIST DEVICE:
A Ventricular assist device, or VAD, is a mechanical device that is used to partially or
completely replace the function of a failing heart. Some VADs are intended for short term use,
typically for patients recovering from heart attacks or heart surgery, while others are intended for
long term use (months to years and in some cases for life), typically for patients suffering from
congestive heart failure.
SAMPLE PICTURE OF LVAD
The major advantage of a VAD is that the patient can keep the natural heart, which can
receive signals from the brain to increase and decrease the heart rate as needed. With the completely
mechanical systems, the heart rate is fixed.
2) Heartmate II:
Heartmate II pumps (which may be centrifugal or axial flow) are smaller and potentially
more durable and long-lasting than the current generation of total heart replacement pumps.
SAMPLE DEVICE OF HEARTMATE II
Blood clotting is still a problem with mechanical valves and manufacturers continue
to improve designs, sometimes using super-computing modeling tools, as well as surgical
procedures. The shape of the orifice is being improved to reduce pressure losses, turbulence
and shear stresses. Flow area is maximized by using stronger materials, which minimizes
wall thickness. Tapering the sides of the valve pumps blood more efficiently. Operations are
also being developed that only require a 3-4 in (8-10 cm) incision instead of 12 in (30 cm).
Manufacturing efficiencies will continue to improve.
Researchers are looking at making heart valves out of plastic material that are
flexible enough to simulate the opening and closing action. This approach may not require
anticoagulation drugs. Others are working on developing artificial heart valves made from a
patient's own cells. Experiments have been successful using sheep. Both developments may
take decades before they are put in practical use.
The heart is the main part in the human body, and its failure causes death. The future of
the total artificial hearts will be a design that allows worldwide mobility and will be similar to the
AbioCor, only redesigned so there is no blood clot, or durability problems. Hoping that there would
be much more development in this field and also decrease in the mortality rate due cardiac failures.
RECENTLY DEVELOPED ARTIFICIAL HEART
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• Reed, Stephen. "Sarasota Doctors Trying Out a Better Artificial Heart Valve."
Sarasota Herald Tribune (June 5, 1998): IA.
• "Researchers Grow Artificial Heart Valves in Sheep." Reuters Ltd (November 7,
• Stemnberg, Steve. "In Medicine, a Shortage Prevented." USA Today (August 3,
• "Medtronic Announces First Implant." Medtronic, Inc.
http://www.medtronic.com(December 29, 2000).
• "St. Jude Medical Announces One-Millionth Mechanical Heart Valve Implant." St.
Jude Medical, Inc. (April 6, 2000). http://www.pmewswire.com(May 2000).
• —Laurel M. Sheppard