ABSTRACT:
??? Heart disease currently affects more than 100? million? people? around? the? World?? Some? of? these? diagnosed ?cases? are? so severe that patients? may not? survive? the wait? for? a? donor? heart.??? Biomedical scientists and? engineers? have? developed devices? such? as? defibrillators, pacemakers, and artificial? hearts to keep patients? alive? until? a? donor ?heart becomes? available.??? Artificial?? hearts prove? to? become? the? most? effective choice for severely ill patients.? In 1995, 2400? heart? transplants? were? performed while? 4000? patients? awaited? donor hearts;? 731? of? these? patients? died waiting.??? With? the? number? of? patients suffering? from? severe? heart? disease increasing? and? the? number? of? donor hearts remaining constant, an immediate need? exists? for? the? advancement? of artificial hearts.? Artificial hearts provide a viable option for patient awaiting heart?? transplantation. Future developments on artificial hearts have the?? hope? of? eliminating? the? need? for the transplantation completely .
? INTRODUCTION:
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????????????????? Artificial? hearts? have? been around? since? the? early? 1980s. TheJarvik-7?? became?? the?? first?? permanent artificial?? heart?? in?? 1982.? The?? patient implanted with?? the?? device?? lived?? for?? 112 days on the artificial organ.? Patient?? was?? unable to leave his bed and was in severe pain until his death. Human life could be? prolonged? by? artificial? means,? but patients? still? had? to? suffer? after implantation. At this time, the risks, such as? sub-standard? quality? of? life, outweighed? future? benefits? of? artificial heart? technology? and? all? research? was put? off? until? positive? results? could? be expected.? After many technological Developments in materials science as well as pharmaceuticals, artificial heart technology is once more in the spotlight. The? Complete? Artificial? Implantable Heart? and? the? Ventricular? assist? device provide? a? mobile? option? for? severely? ill cardiac patients.
2. Heart Anatomy and Disease
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?????????????????????????????????? To? completely? understand? the design? development? of? the? device,? it? is imperative? to? know? the? functions? and diseases of? the? human? heart.?? The heart is the most important organ in the human body.??? Even? if? a? patient? is? considered brain dead, the patient is still considered alive? until? the? heart? stops? beating. Though it serves such an essential role the mechanisms behind the human heart are relatively?? simple.??? The heart is pump that works based on positive displacement.? Positive? displacement refers? to? a? change? in? volume? within? a chamber? due? to? the? movement? of? fluid across its boundaries.? From this volume change,? pressure? differences? arise? that drive? the? blood? pumping? process.? The heart? has? four? chambers.??? These chambers or cavities are the right atrium right? ventricle,? left? atrium,? and? left ventricle.??? Each? chamber? connects? to a one-way valve.? When a cavity contracts, a? valve? opens? and? blood? flows? into? the chamber.? In summary, there? are? four valves,? each? associated? with? individual? chamber.?? The following list identifies each valve with respective chamber.
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The?? heart pumps blood to the body in two steps. First,? the? right? and left? atria? contract,? moving? blood? to? the right? and? left? ventricles.??? Second,? the ventricles? contract? simultaneously? to push? the? blood? out? of? the? heart? and through? the? body.??? The heart then relaxes, allowing new blood to fill the atria.??? This? contraction? of? the? atria? and the? ventricles? makes? up? a? heartbeat. Figure1 illustrates the anatomy of the human heart.? ??
The?? human?? body?? needs?? oxygen in order to live. The circulatory system is responsible for filtering oxygenated blood and deoxygenated blood from the body.? Blood enters in to?? heart through two veins, the superior vena cava and the inferior vena cava. Both?? of these veins feed de-oxygenated blood into the right atrium. The right atrium contracts sending blood to the right ventricle. Blood? flows? from? the? right? ventricle through? the? lungs? by? means? of? the? Pulmonary valve .With in the lungs the deoxygenated blood becomes oxygenated. The newly oxygenated blood flows through left atrium and ventricle, and the blood disperses through the body. Figure 2 recaps flow of blood through the heart.?????????????????????? ?????Like all machines, the Heart can malfunction numerous?? ways. Cardiovascular?? disease? occurs? when? the heart? becomes? ?clogged,? broken? down, or? in? need? of? repair?.??? Severe cardiovascular? disease? is? the? leading cause for heart transplantation,? but other malfunctions? such as? valve damage and chamber problems also? require? the need for?? a? new? heart.?? Currently, 12 million Indians have at least one kind of cardiovascular disease.?? Heart disease is the number one cause of death in India. Since? many? conditions? fall? under? the in?? category? of? cardiovascular? disease,? we will? focus? on? the? two? main? causes? for heart transplantation and artificial hearts: coronary heart disease? and ?congestive heart failure .
Coronary heart disease (CHD) afflicts approximately 20 percent of all patients diagnosed with cardiovascular disease. Patient?s symptoms can range from being mild to intolerable. CHD is the hardening of artery walls inside the heart. Arteries are essentially piping that connects heart valves together. In CHD , the transportation of blood becomes impaired when a mixture of fat and cholesterol, or plaque, lines the arteries the buildup of plaque restricts the free flow of blood, which induces pressure drop between the valves. The heart compensates for this pressure drop by pumping harder in order to provide enough blood for the entire body Patients suffering from CHD often exhibit symptoms such as severe chest pain and fatigue due to the lack of oxygenated blood. For severe cases of CHD, the only cure is a heart transplant .Congestive heart failure (CHF) arises when the heart does not efficiently pump blood. Since the heart is unable to pump enough oxygen-rich blood, blood starts to fill in the lungs, which leads to congestion. Therefore, the heart must work harder in order to meet the body?s oxygen demands. This behavior cause?s excessive wear to the diseased organ initial symptoms of CHF, such as fatigue and swelling of the ankles, is usually so option. Until the condition becomes much more severe. As the disease progresses patients start to suffer from shortness of breath and palpitations even while remaining stationary. For extremely, severe cases, transplantation is the only option.
3.? Effectiveness of Transplantation
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??????????????????????????????? Surgeons started developing heart transplantion techniques early as the 1900s.? Preliminary transplantations conducted on animals proved to? have fatal cosequences caused by the donor organ rejection.Therefore doctors were skeptical to try transplantation procedures on humans.
??????????????????? In? 1905,? the? first? cardiac? heart transplant? was? performed? by? two surgeons? on? a? dog.? They? removed? the heart of a dog? and placed? into? the chest cavity? of? larger? dog? (Transplantation) Then the heartbeat? resumed but the? dog? transplantation. Though the experiment had fatal results,? this? event? stunned? the? medical community? and? spearheaded? further research? in? field? of? cardiac expired? two? hours? after? the? operation.
???????????????????????????????? By definition, heart transplantation is ?The replacement of a patient?s diseased or injured heart with a healthy donor?? heart?.??? Reaching the exact definition of transplantation proved to be an extremely difficult task. ??In order to deter organ rejection after transplantation, research was launched in field of immunosuppressant drugs.??? An immunosuppressant drug restrains a transplanted patient?s immune system to prevent rejection of the implanted organ.
Dr.? Gertrude Elion?? developed the first with end stage cardiovascular disease
in 1957.??? Azathioprine proved to be useful tool that helped facilitate future
advancements in organ? transplantation.
????????????????????????????????????? In 1967, Dr. Barnard performed the first human heart transplant in Cape Town, South Africa.??? Dr.? Barnard implanted the donor heart from a 25-year old? female? into? a? 55-year? old? female with? end? stage? cardiovascular? disease .she? lived? for? 18? days? with? the transplanted? organ.??? Ironically, the medication prescribed to suppress rejection of the new organ weakened his immune system.
???????????????????????????????????? Current? heart? transplantation techniques? prove? to? be? a? viable? option .According? to? the? United? Network? of Organ? Sharing? (UNOS),? 2,202? heart transplants? were? performed? in? 2001? compared to 170 transplants performed in 1970.?? Currently, approximately 70% of transplant patients live for?? five or more years after transplantation [UNOS, 1999].??? These? current? statistics? are staggering? in? comparison? to? the? 14% survival? rate? from? the? early? 1970s.Scientists? and? physicians? have? worked collectively? to? make? transplantation? a?? safe and effective process.failure? patients,? there? are? many limitations to the procedure.? As of now more than 11,163 patients were awaiting heart transplant [UNOS, 2004].?? Only about? quarter? of? these? patients? will receive? a? new? heart? [UNOS,? 2004].Since? there? is? such? a? shortage of? donor hearts.?
????????????????????? ??????????????Therefore, further development provides a solution for all patients. Current development of artificial hearts strives to is necessary to provide a universal solution for these patients.
4. Total Artificial Heart Development
????????????? ??????????????????????????The? development? of? artificial? hearts reflects? a? transition? from? a? support device? to? a? completely? self-contained machine. In the 1960s, the purpose of an artificial? heart? was? to? temporarily support? patients? until? a? donor? heart? became? available.??? Surgeons? attempted successful;? however,? many? surgeons became? wary? of? this? device? because? it early? 1980s? by? implanting? an? artificial heart? intended? for? long-term? therapy. The device they used was the Jarvik-7, a blood pump that replaces the heart?s ventricles.??? The? procedure? was? initially? successful;? however,? many? surgeons became? wary? of? this? device? because? it did? not? offer? an? acceptable? quality? of life.??? As? a? result,? the? public? began? to question? the? need? for?? permanently removing? vital components? of the? heart. The? world of? artificial? heart? technology then? separated? into? two? classes:??? assist devices? and? artificial? hearts.??? In? the 1980s,? several? organizations,? including Abiomed? Inc.,? Penn? State? Medical Center,? and? the? Texas? Heart? Institute, began developing ideas for new designs. Their? intent? was? to? engineer? artificial hearts? that? could? permanently? sustain heart? failure? patients? while? providing? a decent quality of life.?? These companies immediately encountered one huge barrier infection due to precutaneous or skin piercing, tubes. During? the? 1980s,? every? artificial? heart had? power? cords,? blood? tubes,? or? air tubes? protruding? from skin. It was not until the early 1990s with the advent of transcutaneous technology.
Milestones in the Artificial Heart Technology
?????????????????????????????? ?to artificial heart
?????????????????????????????? VAD?s show potential for long term support.
??????????????????????????????? Protruding. Electrical wiring, patients with long-term VDA?s
recovers from heart failure.???? ????????????????????????
?????????????????????????????? patients after implantation.
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