Medical Devices and Electromagnetic Interference : Part 2

by Food and Drug Administration (FDA)

(Page 2 of 2)

FDA engineers found that the wheelchairs' brakes would release and the wheels would begin turning in relatively low-strength electromagnetic fields. A police radio held about a meter away (3 feet, 4 inches) could cause some wheelchairs to move.

In response to this problem, in May 1994 FDA asked wheelchair manufacturers to ensure that all new chairs be at least reasonably immune to EMI (FDA recommends an immunity of 20 volts per meter), that they be labeled with the immunity level, and that purchasers be warned about the possibility of EMI and how to avoid it. FDA has also been working with the Rehabilitation Engineering Society of North America to develop EMC standards for wheelchairs. The goal is to increase the amount of electromagnetic waves the chairs can withstand without malfunctioning (that is, increase the immunity to EMI).

Today, FDA requires all new powered wheelchairs, respiratory devices, and implanted pacemakers to meet rigorous FDA guidelines for EMC before they can be approved. FDA plans to develop guidelines for other medical devices as needed.

It will probably be easier to design and build new devices that are electromagnetically compatible than to retrofit old ones. Some devices can be protected more easily than others. A large x-ray machine or MRI machine, for example, can be placed in a shielded room to protect it from interference and limit its emissions from affecting other devices. A pacemaker, on the other hand, travels with the patient. It must be able to sense tiny electrical impulses from the patient's body without interference from other energy waves in the area.

What Consumers Can Do

Consumers and health professionals who use sensitive medical devices can take steps on their own to protect themselves from unwanted interference. FDA recommends the following:

Be aware that EMI can cause steady, momentary or intermittent disruption of the performance of many medical devices.

Follow the recommendations of the device manufacturer for avoiding EMI.

Purchase equipment that conforms to EMC standards. New apnea monitors, pacemakers, respiratory devices, and powered wheelchairs must meet certain EMI guidelines. Older equipment may not meet them. Not all products are labeled with immunity levels or whether they meet EMC standards. The user may need to contact the manufacturer for that information.

As much as possible, try to keep known sources of interference (such as cellular phones and hand-held transceivers) from coming too close to patient monitors and other sensitive electronic medical devices.

When an EMI problem is suspected, contact the manufacturer of the medical device for assistance. Local clinical engineers (often employed as equipment technicians in hospitals) may also be able to identify and correct the problem.

Report the device problem to FDA's medWatch Program (1-800-FDA-1088) and note if the problem is believed to be linked to interference from a recognizable source of electromagnetic energy in the vicinity.

"FDA certainly has made this a priority," says Witters. "We're beginning to address this across a whole range of devices and that will take some time to do."

In the meantime, he says, consumers should report any problems by calling FDA's medWatch Program and should make a conscious effort to keep sensitive medical devices away from transmitters like cellular phones and walkie-talkies. Says Witters, "The key in dealing with this is awareness."

Cellular Phone Phobia?

The popular television series "ER" ran an episode last fall about a cellular phone wreaking havoc in a hospital emergency room. The electromagnetic waves radiating from someone's phone caused a powered wheelchair to spin out of control and a woman's implant cardiac defibrillator to fire without cause.

This fictional situation is based on a real life problem. Some European hospitals have already banned cellular phones from their buildings, and FDA has encouraged hospitals in the United States to take such action if warranted.

But that doesn't mean these phones should be outlawed everywhere. Though a popular target for blame, cellular phones are likely a small part of the problem, says Don Witters, an FDA physicist and chairman of an agency working group examining the problem.

Cellular phones generate a very small amount of the total electromagnetic waves in the atmosphere. But because of their mobility, these phones have the potential to get closer to most medical devices than, say, a radio station transmitter on top of a hill.

Patients and doctors who routinely use sensitive medical devices should be aware of the problem and consider keeping cellular phones away from their equipment.

The Cellular Telecommunications Industry Association, concerned about the problem electromagnetic interference poses for cellular phones, has given seed money to start a research center at the University of Oklahoma to explore the issue.

About the Author

www.fda.gov
FDA is A United States government body that oversees medical devices, including contact lenses, intraocular lenses, excimer lasers and eyedrops. In the US, these products must be approved by the FDA before they can be marketed.