The Hidden Power of the Artificial Heart

Since ancient times, human have viewed the heart more than just a physical part of the body. It has been thought the seat of the soul, the source of emotion, and the centre of each individual existence. For many years throughout history, the human heart has been regarded as a forbidden organ too delicate and too crucial to withstand the rigor of surgery, thus doctors and medical researchers left the heart untouched. If you think again, what actually brought about the creation of an artificial heart? In my point of view, heart disease have been pointed out as the number one killer in our modern civilization thus making heart disease so severe that the patient may not survive to wait for a donor heart. According to the American heart association, there are an estimated number of 1600 to 40,000 recipients who require a permanent cardiac replacement but unfortunately only 24,000 are available for transplant. Even so the mismatch for blood type, donor heart and potential recipients provides the need for long term alternative. Thus the creation of artificial heart started to develop. If it were to be perfected, it would enable thousands of human lives to be saved. Although there are other electronics devices related to heart failure such as defibrillators, pacemakers and many more cardiac support systems that can be use. This cardiac technology is used temporary on the patient so as to keep them alive until a heart becomes available. The newest inventions of an artificial heart are Abicor a Bi-Ventricular support system and Jarvik 2000(New generation of Jarvik 7).

But what is actually an artificial heart? According to an encyclopedia, the definition of an artificial heart is a mechanical heart which focused on mimicking the natural physiological heart system. Adult human hearts weight approximately around 300-350g and occupy around 300 cm2 of the thoracic cavity. There are four cardiac chambers that are separated by valves, dividing the heart into left and right halves. Under resting conditions, the heart pumps approximately 2.5 litres of blood in approximately 1-2.3 minutes.

According to a research by the National Heart Institute (NHI) in the states, there are several specific criteria for the successful application of a fully artificial heart. Firstly, there must be an adequate volume of blood to meet the physiological needs of the recipient. Secondly, the heart must be properly automatically functioning. In addition, complication such as thrombosis and infection should be avoided directly or indirectly. Lastly the durability of the device function should be considered too.

As well as design criteria, the selection of acceptable material to create this artificial heart is a challenge too. In order to reduce complication while providing durability to device function, the material chosen must be an elastomer so it can be flexible during pumping process. It should also not show any mechanical problem over the device life span in the recipient. The material surface should be acceptably low propensity to prevent thrombosis formation as well as the possible blood compatibility. The material should not Be prone to calcification. The material chosen should be able to form into any complex shape. Impervious to water and water vapour is another factor to consider so as preventing moisture from entering the motor housing. Well the cost of the material is not considered because the quality of the material is detrimental to the life of the recipient, thus cost is unimportant.

As all the design criteria are listed out, the current material available is another thing. Polymer is considered the most promising material around. They can select to a certain characteristic of mechanical resistance, degradability, permeability, solubility, transparency. Poly can be synthesized to have specific chemical, physical and interfacial characteristics. By preparing them in different components, they lead to a variety of properties and structure as compared to other materials. Well in this case of creating an artificial heart, polyurethane is preferred because of its optimal mechanical properties to withstand rigorous vibrational strain. This polymer includes properties such as good elasticity allowing high flexibility of 5.9MPa. It also have an elongation of 850% before breakage, thus it exceeds the amount of elongation necessary to withstand the vibrational cycles. Polyurethane have a low level of water absorption of 1.5%, thus ensures water will not seep into the motor housing. Finally the tensile strength of 41MPa far exceeds the strength requirement.

As the human body’s acceptance to it is highly complex, most polymers have a tendency to form surface thrombosis thus biocompatibility is an issue. Furthermore, segmented polymer urethanes tend to degrade due to environmental stress cracking. In addition, it appears to be relatively permeable to water and water vapour which could result complication in contaminating the motor thus may cause the motor to defunct. The traditional polyether urethanes cannot meet the rigorous requirement of the fully artificial heart. The most major problem is bacterial infection. This is cause by the protein layer mostly of fibrin, resulting from the polymerization of fibrinogen, a process activated by the biomaterial’s surface. Therefore, bacteria can be easy attached to the material and cause infection. Choosing a material that could minimize bacterial infection and limiting protein adsorption is the key here. One such way is to choose a material which is hydrophilic allowing the absorption of water. This characteristic hinders the protein-surface interaction and protein absorption on the surface. By distrupting the absorption of proteins, this causes the material to develop less protein layer thus less likely promoting the growth of bacterial and infection.

As I has stated earlier, the most common material of a total artificial heart is polyether-based polyurethane. However this material cause many drawbacks thus the pursuits of finding a new material is essential. Unfortunately, scientists have been unable to find a suitable substitute which has such mechanical properties as well as relative biocompatibility. Therefore, scientist started to change and improve the characteristic of polyurethane. One possible solution is to synthesize a polymer consisting of polyurethane along with a phospholipids polymer. Research shown that by combining this two polymers together it created a 2-methacryloyloxethyl phosphorylcholine (PMEH) with Segmented polyurethane. These alloys show a significant decrease in protein at the blood interface of about 17% only. Well these alloys certainly restrict the onset of thrombosis. Thus after careful consideration, scientists has shown that although the segmented polyurethane is not a better choice but by enhancing its biocompatibility with phospholipids polymers to form 2-methacryloyloxethyl phosphorylcholine (PMEH). This synthesis polymer shows that it prevents bacterial infection and thrombosis. Although by improving its biocompatibility characteristics, it still maintains its electrometric mechanical properties which are necessary for the rigorous pumping cycle.

Since we had find out what is the design criteria of an artificial heart. Let now look into the evolution of artificial heart technology. In 1958, the first implantable artificial heart was created. Although it is not ready to be implanted in human being, the Dutch-born physician Drs Willem Kolff and a Japanese physician Tetsuzo Akutsu planted this polyvinyl chloride device in a Japanese dog which in turn sustained it for 90 minutes. In 1965, the same medical doctor Drs Willem Kolff started to develop another artificial heart. This time he and his team use silicon rubber. The artificial heart is then being implanted in a calf but it died soon after about 3 days. But after 4 years of trial and error on identifying the problem that occurred, the first artificial heart which is to be implanted in a human being emerged. This 1969 artificial heart is design by Dr Domingo Liotta. The recipient of this heart survived for almost 3 days with it and 36 hours more with a transplanted heart (natural heart) before he dies. Physicians and scientists then began to consider the possibility of creating a permanent, rather than temporary, implanted artificial heart. A more in-depth research on artificial heart brought about the development of jarvik-7 which were design and develop by a team medical doctors which were led by Robert Javik, Donald Olsen and Drs Willem Kolff in 1982. Jarvik 7 permanent design was the first for its kind. Nearly twenty years after the first mechanical heart is created, a new generation of smaller, more efficient mechanical implants emerges. They are Abicor a Bi-Ventricular support system and a similar next generation of jarvik-7 called the Jarvik 2000 was invented.

Through recent years, nobody has talked about the artificial heart after Washington dentist Barney Clark took 112 miserable days to die after being fitted with the Jarvik 7 mechanical heart back in 1982. The suffering included convulsion, thrombosis, kidney failure and respiratory problems and a finally a multi-organ failure. Back then, the New York new times even nicknamed this horrific artificial heart research as “Dracula of medical technology”. In the year 1982, Jarvik 7 was the only artificial heart available that is worthy on being tested on human being. Robert Jarvik called the artificial heart the Jarvik 7 after himself. Made of Dacron polyester, plastic and aluminum, that Jarvik 7 has an internal power system that regulated the pump through a system of compressed air hoses that entered the heart through the chest. The air hoses were connected to the chambers. The internal power system drives the pumps, which pumped the blood through the patient body. Jarvik and his team tested the device on cows and other animals, making sure the heart could consistently beat at least 100,000 times a day. Soon, it was ready to be tested on a human being. Thus a Washington dentist Barney Clark is being made the guinea pig in this medical research. After years of medical advancement, dozen of company and cardiac research centers have been working on an artificial heart that is relatively smaller and safer than Jarvik 7.

In Danvers, a state in the United States of America, A biotechnology company called Abiomed Inc works together with Harvard surgeon Gus Vlahakes to recreate a new generation artificial heart which is completely implantable about the size of a grapefruit. But in the first place why should they take the trouble to recreate such devices which were considered “evil” in the medical arena. Well the answer is simple; the need for such devices is crystal clear. This artificial heart helps to extend the life of a person before a donor heart is available.

Thanks to the advancement of medical technology in Microprocessors, Biomaterials, Batteries and Motor over the past 21 years. Designers in artificial heart have face out the many problems with Jarvik 7. What do you think is the problem with Jarvik 7 that need to be solved? The biggest problem is actually the patient had to tied to an external wind machine and have large hoses piercing the chest thus causing infection in the process. Secondly, the internal design is not smooth thus blood clots could occur. Back in the 80’s, microprocessors is not used thus Jarvik 7 cannot adjust the blood flow to meet the physiological needs of the recipient relatively speaking. In those day rechargeable batteries in not used thus the patient is to be constantly attached to an external electrical source.

After an intensive research, Cardiologist has found ways to keep the invasive medical procedure to the minimum. The Abiomed’s Abicor uses an external energy system which transfer energy to a transduction device attached at the torso. This device transmits power to the internal battery across the skin without any incisions. It also has an internal controller and the electronics system regulates the pumping speed of the heart based on the physiological need of the patient which acts like a microprocessor. It looks like a sphere within a sphere, with the inner ball scuttling back and forth. The external battery which is about the size of a pager is being placed at the wrist of the recipient. Internally in the recipient’s body, there is a rechargeable internal battery which continually recharged from an external battery pack and provides up to unlimited hours of operation.

As the Abiocor heart itself, it is designed to move blood through the lungs and to the rest of the body, stimulating the rhythm of a heart beat. It is about the size of a grapefruit and includes two artificial ventricles with valves and a motor driven hydraulic pumping system. In general the Abiocor looks like a new age artificial heart because the shape and material used is very futuristic and much smaller than an artificial heart usually is. On the other hand, the Jarvik 2000, it runs power through a fixed jack implanted behind the patient’s ear. The internal and external batteries use is lithium like those in had phone which could have slashed the time that a patient has to be hook to an electrical source.

The Jarvik 2000 by contrast uses a miniature rotary pump to replace the left ventricle only which is call a flowmaker that boost the left side of the heart so as to help the natural heart to recover. The biggest different between Jarvik 2000 and Abiomed’s Abiocor is that Abiocor heart take over the whole function of the left ventricle but Jarvik 2000 took only part of the left ventricle work by having a booster pump installed which allow the heart to recover on its own.
Even so, this lab full of highly specialized technicians and physician would seem to ensure success. In the end the first recipient of Abiocor Robert Tools, the first patient to receive an Abiocor heart, lived only 151 days. The individual that received the fourth implant, who according to his family’s wishes, never has been identified to the public, survived only 56 days. Recently, Tom Christerson aged 71 died on Friday, 7th February 2003 after nearly 17 months with the plastic-and-titanium device pumping in his chest.

Well all in all, although millions of dollars, hundred of highly educated medical researchers and countless hours of works is being put into making the perfect artificial heart. It could only extend life only a hundred days or so. Could it be that we had not gave god enough credit for his ability to design and create the amazing human body. Even though man-made artificial heart may hold an array of hope and promise that cardiac patient could live a few more years, but for now I still cling to the heart that god made in the beginning. In considering the full impact of artificial heart on society, we must not narrow our thinking to include only the beneficial possibilities. There exist moral, ethical and economics factors that accompany this new innovation to humanity.