When we see total artificial hearts in science fiction, they are usually metal-and-plastic versions of what we have now, small pumps that magically attach to arteries. But two medical researchers have successfully created working artificial hearts — and they don't beat. They hum.
In fact, they don't look or sound much like the hearts we have at all. Fitted out with two rotors that hum quietly in the chests of several calves and one human who have received the devices, these artificial hearts purify and circulate blood without ever pumping, and therefore without beating either. The story of these devices is a reminder that the best way to imitate nature with machines doesn't always involve directly copying nature's designs.
One of the best examples of this principle is the airplane. Early airplane designers looked to birds for models — and created devices with beating wings. But that turned out to be a costly, ineffective design for artificial birds. And eventually engineers hit upon the idea of rigid, stable wings. Sure, they weren't like their natural counterparts. But they worked. The same notion is behind Texas Heart Institute doctors Billy Cohn and Bud Frazier's total artificial heart, a device cobbled together out of ventricular assist devices and a lot of ingenuity.
In March, after practicing on 38 calves, Cohn and Frazier felt confident enough to try their device on a human patient. They chose Craig Lewis, a 55-year-old who was dying from amyloidosis, which causes a buildup of abnormal proteins. The proteins clog the organs so much that they stop working. In Lewis' case, his heart became so damaged, doctors said he had about 12 hours left to live. His wife, Linda, said they should try the artificial heart . . . Cohn and Frazier did not start totally from scratch. They took two medical implants known as ventricular assist devices and hooked them together.
A ventricular assist device has a screwlike rotor of blades, which pushes the blood forward in a continuous flow. Thousands of people have one of these implanted close to their hearts, including former Vice President Dick Cheney. By using two, the doctors replaced both the right and left ventricles - the entire heart.
"I listened and it was a hum, which was amazing," Linda Lewis says. "He didn't have a pulse."
Tragically Lewis died a month after getting the heart — not from complications arising from the artificial heart, but because the disease attacked his other organs. But Cohn and Frazier gained tremendous insight from seeing the heart operating inside a human, and are working to improve the design. If their work pans out, we may see a generation of people who survive heart disease by going without pulses.
The researchers are currently working on a new design, still incorporating what they call "pulseless pumps," that they hope to submit for FDA approval eventually. Though most researchers are still focusing on total artificial hearts that operate with a pumping mechanism, Cohn and Frazier are dubious that functioning artificial hearts will "beat" the way biological hearts do.
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(Thanks for the tip, Mary Knight!)