By Astra Kristina B. Mallari
Philippine Science High
School-Western Visayas Campus
"When a good-looking blonde walks down the street, your heart speeds up. To make mechanical hearts respond to a blonde will not be so easy." -Adrian Kantrowitz, M.D.
There are times when the lives of people who suffer heart disease are endangered. Most of the time, severe cases need a heart transplant, and donor hearts are just not available. This may cause the loss of a life. But not anymore, because luckily, scientist have invented artificial hearts that patients can use until a real heart comes along.
Artificial hearts are able to perform the functions of a real heart. The difference lies in the fact that the heart is our living organ, while the artifical heart is made up of plastic, aluminum and Dacron polyester. Because it is artificial, it needs something to power it up, so an outside source is needed. The power used energizes and regulates the heart by using air hoses that goes through the heart to the chest.
Jarvik - 7
The best known artificial heart is the "Jarvik - 7" artificial heart, named after its designer, Robert K. Jarvik, an American physician. Designed to function like the natural heart, the Jarvik - 7 has two pumps (like the ventricles), each with disk-shaped mechanism that pushes the blood from the inlet valve to the outlet valve. The Jarvik - 7 was first used during the early 1980s.
In 1982, an artificial heart was successfully implanted on a long - term basis in a human patient. The operation team was led by William DeVries of the University of Utah and the patient was Barney Clark. He survived the Jarvik - 7 for 112 days. He died because of other medical complications, not because of the artificial heart implanted in him.
History of Artificial Hearts
Although the use of artificial hearts flourished in the 1980s, earlier artificial hearts date back to the mid-1950s. But as early as 1939, a movie has been made about the research on artificial hearts. In 1957, a team of scientists, led by Dutch physician Willem Kolff (the man who developed the first effective artificial kidney) and Dr. Bert Kusserow, another physician, tested their model on animals to identify problems. They had achieved success with artificial hearts in dogs, and others throughout the world started performing similar experiments on a variety of animals. In 1969, a team led by Denton Cooley of the Texas Heart Institute successfully kept a human patient alive for more than sixty hours with their model. Because of these breakthroughs, the dream of a permanent artificial heart seem easy to turn into reality.
Developments in the Research of Artificial Hearts
A. Heart Assistance Devices
There are several types of heart assistance devices which have been developed, all of them based on the principle of helping the failing heart do its job of pumping. Some of these devices are temporary, such as DeBakey's, while others, such as Kantrowitz's, are permanent. The obvious question is: Why replace just a part of a failing heart if it can be entirely replaced?
Dr. Kantrowitz, whose remark about the response of the natural heart to the sight of the blonde walking down the street is quoted at the beginning of this article, believes that it is better to leave the heart in place to respond to all these signals amd make a mechanical pump an auxiliary device to do most of the work.
The basic idea behind the temporary assist devices is to allow the heart to recover its strength and resume its functions without further mechanical help. The booster devices are designed to permanently supplement those hearts which are incapable of functioning on their own.
B.Total Artificial Heart
What Willem Kolff has devised is a total heart replacement involving two separate air-driven pumps, one sending blood to the lungs for oxygenation, the other pumping fresh blood to the body. The lining of the pumps is of silicone rubber, and anticoagulants must be be used constantly to prevent clots from forming. This is still a major drawback to the completely artificial heart, for surgeons dislike relying too heavily on the anti-clotting drugs. The total artificial heart, no doubt, will be an able substitute for cardiac transplantation.
Material for the Artificial Heart
Most materials used in artificial hearts have tended to damage red blood cells and promote clotting, which holds them back from clinical use in patients. However, work is in progress to provide a natural lining which would not affect the blood passing through.
The ideal material, according to a report prepared by the Natural Heart Institute,
...should not modify blood or tissue electrolyte composition
...should not cause allergic or toxic reactions
...should not interfere with the body's normal defense mechanisms, not cause or promote the development of cancer, nor otherwise harm the blood or tissues.
It must be tough and durable enough to retain its basic physical characteristics through ten years or more of hard wear in continuous contact with blood and probably, with the working fluid which drives the pump.
Along with this search for the ideal material, researchers will have to achieve a better understanding of the basic clotting process and the mechanical, electrical and chemical influences that affect it. Early experience with artificial heart valves showed that certain surfaces apparently irritated the blood that they caused it to clot on these surfaces.
Power Sources
An artificial heart or an assistance device intended for long-term use in patients who will leave the hospital and resume normal living requires a self-contained source of energy. The early models of the assist pumps, as well as the artificial hearts implanted in animals, were powered from outside the body, with wires or tubings running from the source through the chest wall to the device. In addition to being unwieldy and cumbersome, such external sources create the problem of irritation of the chest opening and possible infection.
The ideal energy source would be an implantable biological fuel cell which would convert natural sources of body energy, such as glucose, into power sources for the artificial heart. Enzymes or catalysts would speed conversion of the body fuel to electrical energy, and according to the Natural Heart Institute report, "the combustion of the metabolic fuel would occur at normal body temperature and the 'ashes' would be metabolites normally disposed of by the body. A sufficient quantity of fuel could be assured by appropriate modifications in the diet, if these proved necessary."
Future of the Artificial Heart
The patient suffering from coronary artery disease presents a challenge to his physician. Diet, exercise, and medical management often work well, so why subject him to the trauma of replacing his heart, unless his has deteriorated so that it can't be saved? And if a patient with a defective valve can be helped by an artificial replacement, this is better than inserting a transplanted heart or an artificial heart.
Though it entails a lot of problems, artificial hearts and transplants will continue to catch the imagination of the public, perhaps because they are so dramatic, so extreme. These are extreme measures, which even the most daring surgeon will use sparingly. They are only holding actions until the development of effective methods to overcome and prevent heart disease medically. Tampering with the body's chemistry is considerably gentler than carving open a patient's chest and operating on his already-fragile heart.
When medicine fails, then surgery can step in. The bold, imaginative surgeons who have made heart transplants and artificial hearts a reality are far ahead of their medical colleagues who are still struggling to unravel the chemical and mechanical influences of heart disease in order to treat it and prevent it.