Wireless power for heart implants could reduce infections, increase mobility
By Ben Coxworth
July 14, 2011
While implantable heart pumps may buy some time for people waiting to undergo heart transplants, such implants have at least one serious drawback - because they receive their power from an external source, a power cord must protrude through the skin of the patient's belly. About 40 percent of patients experience infections of that opening, which often require rehospitalization, and in extreme cases can even cause death. The presence of that cord also makes it impossible for patients to swim or take baths. Researchers from the University of Washington and the University of Pittsburgh Medical Center are attempting to put an end to the troublesome cords, however, by developing a system that wirelessly transmits power to heart pumps.
A team led by UW associate professor of computer science and electrical engineering Joshua Smith, along with UPMC heart surgeon Pramod Bonde, created the prototype for the system. It utilizes a transmitting coil that sends out electromagnetic waves at a specific frequency, and a receiving coil that absorbs the energy from those waves, which it stores in a battery. It's a variation on the inductive power technology used in devices such as cell phone charging pads, the difference being that with those devices, the tool and the charger must be touching and held firmly in place.
The UW/UPMC system gets around that limitation, by automatically adjusting the frequency and other parameters as the transmitter and receiver move apart, or change orientation relative to one another. Presently, the wave strength is able to remain constant over a distance equivalent to the length of the transmitting coil. If a one-foot coil is used, for instance, that means it can effectively transmit power to the receiver over a distance of one foot.
If that coil were only a few inches long, that would still be sufficient for a scenario in which it were worn in a vest against the body, with the receiving coil adjacent to it, implanted under the patient's skin. Because energy would be stored in an implanted battery, that means the patient could spend periods of about two hours without having to even be near the transmitter, so they could do things like swim or bathe.
So far, the researchers have been able to use the system to power a heart pump submerged in water. Power was transmitted at about 80 percent efficiency, to a receiving coil that was just 4.3 centimeters (1.7 in) across. Animal trials are now being planned.
Ultimately, the UW/UPMC team would like to see a system in which several transmitters were located around a room, so a patient within that room could move freely about. They also believe that the technology could be used to power other types of implants, recharge consumer electronics, or even recharge underwater instruments in the ocean.