Artificial hearts weren't designed to handle this load. They were supposed to work as temporary stop-gaps that kept patients alive until they could receive a heart transplant. Instead, today's cardiac patients may carry an artificial heart for over a year, leading almost 40 percent of patients to develop dangerous infections around the area where the device's power cord exits the body.
Since sticking a finger into an electrical socket doesn't work so well, many patients still need a safer means of recharging their artificial heart. To solve this problem, a group of researchers have just cut the cord out entirely, relying instead on a system of wireless power stations at home and in the office.
Joshua Smith, an associate professor of computer science and electrical engineering at the University of Washington, and Dr. Pramod Bonde, a heart surgeon at the University of Pittsburgh Medical Center, designed the wireless heart power device. The concept is a variation on inductive power, in which a transmitting coil sends out electromagnetic waves at a certain frequency and a receiving coil absorbs the energy and uses it to charge a battery. Electric toothbrush charging stations and cell phone charging pads use a similar system, except that in both those cases the tool has to actually touch the charger and be held in a fixed position.
"Most people's intuition about wireless power is that as the receiver gets farther away, you get less power," Smith said. "But with this technique there's a regime where the efficiency actually doesn't change with distance."
In what Smith calls the "magic regime," power stays constant over distances about the same as the diameter of the coil — meaning a one-foot transmitter coil could deliver consistent power over a distance of a foot, or a four-inch coil could transmit power over a distance of four inches. That's not far, but it's enough to bridge the skin and tissue to reach a medical implant.
Using the wireless system means no power cord poking through the skin, dramatically reducing the risk of infection and improving the patient's quality of life. Researchers envision a vest that could hold an external transmitter coil connected to a power cord or battery.
A small receiver coil implanted under the patient's skin would connect to a battery that holds enough power for about two hours, meaning the patient could be completely free for short periods of time to take a bath or go for a swim (current users of heart pumps cannot do either). Longer term, the researchers imagine additional power transmitters placed under a patient's bed or chair, allowing patients to sleep, work or exercise at home unencumbered.
"The potential for wireless power in medical fields goes far beyond powering artificial hearts," Bonde said. "It can be leveraged to simplify sensor systems, to power medical implants and reduce electrical wiring in day-to-day care of the patients."