Wireless Power Could Cut Cord For Patients With İmplanted Heart Pumps

Mechanical pumps to give failing hearts a boost were originally developed as temporary measures for patients awaiting a heart transplant. But as the technology has improved, these ventricular assist devices commonly operate in patients for years, including in former vice-president Dick Cheney, whose implant this month celebrates its one-year anniversary. Prolonged use, however, has its own problems. The power cord that protrudes through the patient's belly is cumbersome and prone to infection over time. Infections occur in close to 40 percent of patients, are the leading cause of rehospitalization, and can be fatal.

Researchers at the University of Washington and the University of Pittsburgh Medical Center have tested a wireless power system for ventricular assist devices. They recently presented the work in Washington, D.C. at the American Society for Artificial Internal Organs annual meeting, where it received the Willem Kolff/Donald B. Olsen Award for most promising research in the development of artificial hearts.

Joshua Smith, a UW associate professor of computer science and electrical engineering who moved to the UW from Intel Research Seattle, has for the past six years been working on wireless power. 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.

Smith and colleagues at the UW and Intel devised an inductive system that adjusts the frequency and other parameters as the distance or orientation between the transmitter and receiver coils changes, allowing for flexible yet efficient wireless power over medium distances.

"Most people's intuition about wireless power is that as the receiver gets further 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.

Four years ago, Smith's system attracted the interest of a heart surgeon who had been experimenting with using traditional induction to transfer power, but was hampered by misalignment, unwanted heat generation, and ranges that were limited to a few millimeters.