What can be done when the heart becomes sick or damaged? Sometimes a ventricular assist device can be used to reduce the heart’s work load until it recovers normal function. Both ventricular assist devices and total artificial hearts can be used to buy time until a suitable donor heart can be found for transplantation.
Heart transplants offer the best hope for long term survival and a return to normal activities. Or even extreme activities; Kelly Perkins became famous as a mountain climber after receiving a heart transplant. Today, more than two-thirds of heart transplant recipients can expect to survive at least five years. According to some observers, the average heart transplant recipient can expect to live 15 years. The longest surviving heart transplant recipient was Tony Huesman who lived 31 years before succumbing to cancer.
The first heart transplant was attempted in 1964 when Dr. James D. Hardy at the University of Mississippi Medical Center implanted the heart of a chimpanzee in the chest of a dying man. The primate heart beat for about 90 minutes before stopping. The highly publicized procedure discouraged further xenografts (transplants between species) but spurred interest in human heart transplants.
Christian Barnard at Groote Shuur Hospital in Cape Town, South Africa performed the first human heart transplant in late 1967. A 54-year old grocer, Louis Washkansky, survived 18 days before succumbing to pneumonia. Less well known is the fact that three of Barnard’s heart transplant patients lived more than 20 years.
Barnard also devised and performed the first heterotopic heart transplant—an operation in which the recipient’s sick heart is left in place and the donor heart is connected to it producing a sort of “double heart.” The advantage of the heterotopic operation is that it gives the recipient’s own heart a chance to recuperate and, theoretically, makes it easier to replace a failed donor heart.
This chapter also traces the development of kidney dialysis machines, artificial hearts, ventricular assist devices, artificial joints, and brain-computer interface chips. Though results from cochlear ear implants have been mixed, we are clearly on the right path, and artificial vision—whether using artificial retinas or sensory substitution—is just a matter of time.
But there is more good news.
Imagine a material that can be fashioned into almost any shape, is highly biocompatible, and stimulates the body to grow replacement natural tissue. Such a material would be a boon to repairing the human body. A material with those qualities was discovered by biomedical engineer Leslie A. Geddes, a Professor at Purdue University who passed away in late 2009. Among the honors Geddes received for his many accomplishments were the IEEE Edison Medal in 1994 and the 2006 National Medal of Technology. I am deeply indebted to Professor Geddes, who encouraged me to call him when I had questions, and whose many articles and patents proved a treasure trove of information.
Like many great discoveries, this one was serendipitous. In 1983, Geddes and undergraduate engineering student Michael Voelz tried oxygenating blood using the small intestine of a dog. It worked, but not very well. However, the experiments gave Geddes another idea. He recalled that blood from an ulcerated small intestine does not clot. He also knew that animals and humans have a good deal of small intestine material. Might the small intestine be a source of material for vascular grafts?
Geddes obtained a $50,000 grant from the Showalter Trust and assembled a team to pursue the research. After a false start, they scraped the small intestine leaving only non-cellular material called small intestine submucosa (SIS). They found that because SIS contains no cells it does not provoke an immune response—even when used in different species.
Next, the team implanted pig-derived SIS grafts in the carotid arteries of a number of dogs. Later, no evidence of SIS could be found at the implantation sites. Tests suggested the SIS turned into host tissue.
SIS has since been used in a wide range of applications—from bioartificial heart valves to hernia repair to treating wounds. It has also been used as a dura mater substitute for covering the brain and to augment bladder volume; in the latter application, the remodeled SIS becomes innervated and contracts well.
The human body is a complex system and there are many challenges to repairing, assisting, and replacing body parts. Though our current capabilities are quite primitive, progress has been made in areas that once seemed unlikely. Who would have thought, for example, that material from a specific organ could be transplanted between species and stimulate growth of replacement host tissue in the process?
Next time: The Vision Thing
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