Unplugging the Artificial Heart

Jasper Han | jasper.han@yale.edu July 1, 2014

Imagine if you could not shower. It is hard to imagine for most Americans, who on average shower at least every other day. But thousands of Americans cannot get near water without risking debilitating infection or worse.

A person in this subset of the population cannot shower because a wire runs through an incision in his chest, connecting a battery pack to a device next to his heart. So what should he do? Pull out the wire? For him, doing so is equivalent to pulling the plug. He lives without contact with water; walking in the rain is dangerous, showers at best consist of pat-downs with moist towelettes, and swimming is impossible. These people who cannot touch water are those with heart conditions, whose hearts, without implanted devices wired to a battery to keep them pumping, would stop.

As implausible as a life away from water may sound, more than 40,000 people with incurable heart disease live that way. Every year, roughly 50,000 people worldwide require heart transplants, but only 5,000 of them actually undergo the surgery because the supply of organs does not meet the demand.

Many of the patients unable to receive a transplant resort to left ventricular assist devices (LVAD) to bridge the gap between the onset of the disease and the time of transplantation. Some patients, due to organ supply shortage or incompatibility with the donor, cannot ever undergo transplant surgery and live with the implanted device indefinitely.

The new proposed LVADs, using the Free-D wireless power system. Photo credit: Shuncong Gu

The new proposed LVADs, using the Free-D wireless power system. Photo credit: Shuncong Gu

 

The Traditional LVAD

The LVAD is a type of heart assistance device. It helps to pump blood from the left ventricle to the aorta, and from there to the rest of the body. Inside the device, an electric current runs through coils of wire, creating magnetic fields that exert a force on a hydromagnetically suspended rotor and causing artificial blood flow.

The issue with such devices lies in the power supply: an ungainly three-pound battery is connected to a wire, called the driveline, which extends through an incision into the chest. Even for the most careful patients, the driveline often causes problems such as impaired movement, infection, and even further injury.

 

An Innovation in Wireless Power

While the search for some internally powered ventricular assist device system is ongoing, an innovative wireless external powering system has been developed. Dr. Pramod Bonde, Assistant Professor of Cardiac Surgery at Yale, proposed the Free-range Resonance Electrical Energy Delivery (Free-D) wireless power system.  He worked closely with his collaborator from the University of Washington, where he is an affiliate Assistant Professor of Electrical Engineering. Based on resonance inductive coupling, the Free-D system allows for power to be wirelessly conveyed to the device pumping the heart. Thus, the Free-D system removes the need for dangerous incisions and drivelines.

Though the idea of powering a device using resonance is seemingly complex, the actual concept is simple. To power a LVAD, a recipient coil in the body receives a magnetic field generated by a coil of wires outside the body. Just as a radio picks up on radio waves to produce the music that we hear, the internal coil picks up on the external magnetic field to generate an electric current within the heart. As an analogy, consider a crystal glass (the recipient coil) and a soprano singer (the external coil power supply). When the soprano sings the earsplitting final note of a song (the magnetic field), and the pitch matches the resonance frequency of the glass, the energy generated by the soprano’s voice is transferred to the glass. If the energy is great enough, the glass will shatter.

Specifically in this system, an external coil tuned to a certain resonance frequency contains alternating current (AC) — the type of current capable of being transmitted through wires or by induction — which generates a large magnetic field. When coupled with a second coil inside the patient’s body that has been designed to have the same resonance frequency, the magnetic field induces an electric current through the second coil. The current, still in AC form at this point, can then be converted into direct current — the version of electricity that is usable in devices such as the LVAD.  This type of high throughput energy transmission, using two coils of same resonance frequency, is able to transmit up to 70% of the energy that is initially put into the device.

 

A Safe System

Some might worry that having a magnetic field generated by a device so close to the heart could be damaging to the organ. But compared to other devices with which we are more familiar that emit magnetic radiation, the Free-D system is nothing to worry about. Although the Free-D system has yet to become FDA-approved, the magnetic fields it induces are roughly 8 x 10-5 Tesla in strength. As compared to the magnetic field emitted during a standard MRI, the magnetic force created by the Free-D system is quite small. Our daily exposure to the magnetic field of the earth is about 3.1 x 10-5 Tesla; exposure to the slightly larger field of the Free-D system is equally harmless.

While developing the system, Bonde took several precautions to prevent possible complications. A prominent concern was that the connection would be too short-ranged, and therefore would not allow patients to move very far from the site of the signal transmitter. This issue was addressed by creating transmitters capable of amplifying the magnetic field at the same resonance frequencies, for longer-distance reception.

Despite this improvement, the system still limits the distance a patient may travel. However, amplifying the system creates a magnetic field that can travel through the vast majority of substances. Therefore, if the system is installed in a house, the transmitter can be installed in the furniture and walls and power the hearts of patients as they walk around the room.

As with all fields, the magnetic field induced by the current running through the wire exists at all times and is distributed around the generator, unlike a wave or ray. The magnitude of the electric field at a certain distance away (measured by the Lorentz Force Laws) can be determined, and therefore the transmitter’s signal can be engineered to cover a patient’s entire house.

 

The Implications for Patients

For patients with heart disease, a wide range of applications exists. In addition to extending patients’ lives until they may receive a transplant, this wireless system opens the way to VADs as a permanent alternative to transplants by eliminating the need for a wire through the chest and all the resulting safety risks. Limitations still exist, as there is still a range of allowable movement or a portable battery to carry. Bonde recognizes that though this technology is a step forward, it is not a cure. “This is not a transplant,” Bonde said. “Like all treatments, the patient needs to follow some rules.”

But this technology, though still limited, demonstrates the efficacy of wirelessly powered devices that are implanted within a person. Fascinatingly, using the simple and well-known concept of magnetic resonance induction, Bonde has addressed a complex and multifaceted problem. Though it has far from completely solved the problem of heart disease, this technology opens the way for more innovative and integrated solutions for medical problems.

Not only have Bonde’s recent studies proven that this system may work as a possible alternative to the current models of LVADs; they also prove that, in fact, this system does work in facilitating the lives of heart disease patients as observed in real-life examples. The only barrier remaining that prevents this device’s widespread usage by heart disease patients is approval from the FDA which, according to Bonde, “takes a lot of money.”

However, the actual cost of the device is forecasted to save patients money; though the wireless device may cost slightly more than its predecessor, this amount is more than regained. Without the need for redressing the chest incision, medication for possible infections, or professional assistance with daily activities like showering and sleeping, the life of a heart disease patient is both less expensive and more free.

Does this mean the patient is completely healed? No. Can the patient go skydiving? Definitely not. But the patient can shower and swim, and his lifestyle becomes significantly more mobile. Thanks to a clever usage of electromagnetism, the Free-D system has the potential to improve the difficult lives of heart disease patients without transplants.

 

Acknowledgments:

The author would like to thank Dr. Pramod Bonde for his time, helpfulness, and enthusiasm for his work.

 

About the Author:

Jasper Han is currently a freshman in Morse College.

 

Suggested Additional Reading:

Waters, B.H.; Sample, A.P.; Bonde, P.; Smith, J.R., “Powering a Ventricular Assist Device (VAD) With the Free-Range Resonant Electrical Energy Delivery (FREE-D) System,” Proceedings of the IEEE , vol.100, no.1, pp.138,149, Jan. 2012