In 1994, the television show "ER" aired an episode that showed a cellular phone causing a powered wheelchair to spin out of control and a woman's implanted cardiac defibrillator to fire inadvertently. The havoc wreaked in the fictional emergency room was nothing compared to what happened next when the news media took up the call.

There were Congressional hearings, alarming TV and print news headlines, and even an erroneous national news wire story alleging that cellular phones had caused deaths in hospitals.

Because of the heightened concern, some hospitals across North America chose to simply ban the use of wireless phones inside their buildings. Some hospitals continued the ban. But this may be a case of treating the symptom, not the disease. The solution isn't a blanket ban on wireless phones or other devices. Rather, it's managing the environment in which medical devices operate. The goal should be electromagnetic compatibility (EMC)—making sure that a product operates in its intended environment without being affected by other electronic products or being a source of interference itself.

With the proliferation of electronics and microprocessors in all kinds of devices, it is important to be aware of the possibility of electromagnetic interference (EMI). It's equally important that biomedical engineers and hospital administrators understand how to most effectively manage a medical environment to ensure compatibility and peak performance.

The U.S. Food and Drug Administration's Center for Devices and Radiological Health (CDRH) has been investigating incidents of device EMI and working on solutions since the late 1960s. Extensive laboratory testing by CDRH and others shows that many devices can be susceptible to problems caused by EMI. Donald Witters, chairman of the center's Electromagnetic Compatibility Working Group, has said that "the key to addressing EMI is the recognition that it involves not only the device itself but also the environment in which it is used, and anything that may come into that environment."¹

In addition to FDA, Canadian wireless carriers, researchers, hospitals, and government representatives have been exploring EMC issues. A number of international standards bodies and professional societies also address these issues. They include the Institute of Electrical and Electronics Engineers (IEEE), the Electromagnetic Compatibility Society, the American National Standards Institute (ANSI) Standards Committee 63 Working Group on Medical Devices, the Society of Automotive Engineers EMI Standards Committee, the Bioelectromagnetics Society (BEMS), and the Association for the Advancement of Medical Instrumentation (AAMI). Membership in these organizations includes academic, government, and industry scientists and engineers who specialize in electromagnetic interaction.

Julius Knapp, chief of the Policy and Rules Division at the Federal Communications Commission (FCC), has been active in addressing medical device EMC issues, including interference to hearing aids from wireless devices, interference to medical telemetry devices from new digital TV and future land-mobile operations, and identifying new frequency bands for medical telemetry devices.

In his 1998 keynote speech to the forum on "Continuing Progress in Medical Device—Wireless Compatibility," sponsored by the University of Oklahoma Center for the Study of Wireless Electromagnetic Compatibility, Knapp said that several factors are making compatibility difficult. These include proliferation of new devices, mobility, the trend to digital, and the reliance on weak signals.²

Discussing the unprecedented pace of changes in medicine technologies as well as new wireless-frequencies management, services, and technologies, Knapp said that the key to ensuring compatibility is identifying problems, performing scientific studies, developing solutions, and promoting awareness and education.

For the past five years, the University of Oklahoma's Wireless EMC Center has conducted research into the effect of wireless phones on hearing aids, cardiac pacemakers, and other life-supporting medical equipment. This work has led to a better understanding of and additional research into managing EMC in medical environments.

To varying degrees, all digital wireless technologies have the potential to interfere with hearing aids, as can fluorescent lights, computers, and other electronic devices. In an effort to determine the extent of the interaction of new digital wireless phones with hearing aids, the EMC Center conducted a two-phased study in cooperation with the Hough Ear Institute in Oklahoma City, OK.³

Considered the most comprehensive scientific effort to date in the United States to involve a diverse group of hearing-aid users, the EMC Center's study showed that all three of the digital wireless technologies, when tested in the worst-case (maximum-power) situation, would interfere with hearing aids. Analog cellular phones tested did not interfere with any of the hearing aids.

The degree of interaction varied depending on factors such as phone technology, hearing-aid type, hearing-loss configuration and severity of hearing loss, or as a combination of these factors. Under the most extreme conditions, hearing-aid users—on average—did not experience annoying interaction due to phone signals unless the phones were within 24 inches of the person. The threshold distance to detect any interaction (not necessarily annoying) was 1 m (3.3 ft) between the hearing aid and the phone.

One important finding of the hearing-aid study that can be used in managing EMC is that the elimination of interaction always involves power, distance, and shielding, or some combination of the three.

The Oklahoma EMC Center conducted a large-scale in vitro investigation of interaction between wireless (personal communications services [PCS] and cellular) phones and cardiac pacemakers. The test results, announced in September 1996, show that several pacemaker models had no interaction with any of the phones tested and that a relatively small number of pacemaker models experienced the most interaction.⁴

Less than five percent of the more than 8000 different pacemaker-phone interaction tests exhibited any interaction. Even when an interaction was observed, the pacemaker returned to normal operation as soon as the phone was removed from the near vicinity.

Twenty-nine implantable pacemaker models from five major pacemaker companies, which account for more than 90% of the U.S. market, were tested with 10 different test phones from six major manufacturers of U.S. cellular and PCS phones. In all, five wireless technologies were represented in the test.

Testing was conducted in a closed, electromagnetically shielded room at the Lucent Technologies Test Site in Oklahoma City, OK. Simulated functioning of the heart-pacemaker system was accomplished through the use of a torso simulator and various test equipment items that generated and monitored electrical signals. All testing was conducted under the most extreme conditions—with the phones at their highest power and pacemaker sensitivity set to the maximum value permitted.

The testing showed that a variety of solution approaches are possible to eliminate the potential for interaction between the phone and the pacemaker. These solutions include various types of EMI filtering at the input stages of the detection circuitry. Testing continues in an attempt to further define the minimum separation of the phone and pacemaker that prevents interaction.

Under the most extreme conditions, there was appreciable interaction of pacemakers only with a proprietary 11 Hz TDMA phone, which is not in mass commercial use by the general public. No interaction occurred during tests with analog phones, and comparatively little interaction occurred with other digital standards.

One key finding in the second phase of the study, according to EMC Center researchers, is that interaction only occurred when certain phones and pacemakers were 3 in. or less apart. This is half the distance previously thought.

In another study, published in late spring of 1998, the University of Oklahoma Wireless EMC Center found that interaction may occur between a small number of wireless phones and some implantable cardioverter defibrillators (ICDs). These products are the electronic devices inserted within a patient's body to monitor and correct abnormally fast heart rhythms.⁵

While the study was limited in scope, no interaction was found between ICDs and phones that operate in the 1800- and 1900-MHz bands. The interaction that did occur was mostly between one company's ICDs and one phone technology, and no permanent reprogramming of any ICDs occurred.

The testing involved all of the analog and digital wireless phone technologies operating in the United States and Europe and ICDs from four of the industry's manufacturers. Most but not all of the ICD-phone combinations were tested under the most extreme situations of maximum device sensitivity and phone power output. The phones were tested in close proximity to the ICD to represent the phone carried in a chest pocket or held adjacent to the chest.

If the two ICDs from one company were excluded from the results, along with tests involving 11 Hz TDMA phone technology, the remaining test combinations produced no interaction at all. The 11 Hz TDMA phone technology, which is used for specialized business applications such as trucking, delivery, and construction, and not widely used in the United States, had the most interactions.

Since the study, 11 Hz TDMA, which operated at higher power (1 W maximum) than standard wireless phones, has been refined to operate at cellular power levels (0.6 W maximum). This should reduce the incidence of interaction.

The ICD with the most interactions is now marketed under additional FDA labeling restrictions regarding separation between the wireless phone and the ICD. This ICD also interacted with analog phone technology, the most prevalent cellular technology in use in North America. However, interaction with analog was the least frequent of all the tests. It occurred only with one ICD, and did not occur at distances greater than 1 in. between the phone and the ICD.

The study shows that the use of proper summary measures for comparison is important. While more effective electronic filtering and shielding of the ICD may be a viable solution to mitigate the interaction, the Center concludes further research should be done with additional ICDs and phones, as well as new (untested) ICDs or modified ICDs.

In addition, there should be height testing to accurately address how far away a wireless phone should be kept to prevent any potential interaction with an ICD implanted in a body. In the meantime, researchers recommend a minimum separation distance of 6 in.

Oklahoma EMC Center researchers have developed a number of educational and analysis tools that can be used to manage EMC in hospital environments. In its recently published report, "Electromagnetic Interference Management in the Hospital Environment—Part I: An Introduction," researchers at the Center offer 10 steps that hospital administrators and clinical engineers can take to manage the effects of electromagnetic interaction of wireless devices with medical devices.⁶ The following summary of these recommendations should be of interest to manufacturers as well.

EMC can be readily achieved in medical environments. The long-term solution is to establish immunity standards that require medical devices to operate as intended in the presence of external electromagnetic fields.

In the meantime, hospitals can reduce the potential for unwanted interactions by requiring medical equipment manufacturers to certify the immunity of their equipment, by shielding or replacing vulnerable equipment, and by training staff to be alert to the potential for interference to sensitive equipment.

Wireless system design may also be used to lower the transmitting power of the phones in areas where sensitive equipment is located. When the potential for interaction has been minimized through improved immunity for medical devices and reduced transmitting power of the phones, wireless phones and medical devices can coexist for the benefit of hospital staff,
patients, and their families.