A real and present wireless danger Book Abstract
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Published: April 14, 2007
Cellular phones have quickly become the essential part of our everyday lives. It is not surprise that last couple of years we see more reports that medical equipment doesn’t work properly because of cellular phones. Cellular phones cause harmful interference for medical equipment. This is serious problem that can cause anything from minor inconveniences to serious injuries or even death.
There are number of studies that show if cellular phone is being used near a cardiac pacemaker, it causes interference. It was proven that little more than a quarter of all patients with implanted pacemakers could have problems if they are using digital wireless phones. Good news is that distance of only 8 inches from the phone is needed to make sure that digital wireless phone doesn’t cause any problems. Another interesting fact is that only those phones that operate in 900 MHz frequency can cause problems. Phones that operate in 1800 MHz frequency don’t cause any problems.
All patients with pacemakers need to make sure they don’t carry phone close to the pacemaker. Another good news is that mostly all new pacemakers that are currently manufactured are guaranteed to be safe to use near cellular phones.
Also, there were other tests done with implanted medical equipment that helps patients to inhale. Forty-one patients were tested using digital 900MHz phones. Those tests prove that none of the patients had any problems. The tests were double checked by testing same medical equipment close to a field of cellular-phone antennas. Second test however indicates that strong magnetic field caused by lots of cellular phone power can cause temporary shutdown of implanted medical equipment. Therefore it is recommended for patients with implanted inhalation medical equipment to keep at least small distance between them and digital cellular phone.
Nine of external pacemakers from four different manufacturers were also tested. They showed lots of different problems, which were caused by digital cellular phones and by other personal-communication devices. Therefore, using any type of cellular phone next to a patient with breathing problems, who is treated with temporary cardiac pacemaker, can be very dangerous.
In March of 1998 Texas TV station started testing its new digital TV system. This caused major problems at Baylor University Medical Center and Methodist Hospital. Interference from digital TV signal severely disrupted the operation of low-power wireless heart monitors. They use the same frequency band as new digital TV system. This interference prohibited nurses from monitoring their heart patients. Fortunately, no patient was injured.
However, this served as a wake-up call for healthcare providers, equipment manufacturers, and for government agencies.
In July of 1999, Federal Communications Commission (FCC), which regulates radio-frequency spectrum, met with representatives from various parties that were affected by this problem. This was an excellent example of cooperation between industry and government. The FCC proposed to establish a Wireless Medical Telemetry Service. This proposal would allocate certain frequencies, which would primarily be used to make sure that potentially life-critical medical equipment could operate without interference from other sources.
When the new FCC rule becomes a reality, it will be the first time in the history of the US that wireless medical telemetry will be primary user of the radio-frequency spectrum.
(Wireless medical telemetry is defined as the measurement and recording of physiological parameters and other patient-related information via radiated bi- or uni-directional electromagnetic signals.)
Although the above-mentioned scenario is unique to the introduction of digital TV, wireless systems-including cellular phones, handheld transmitters-receivers, and vehicle transceivers-receivers are one of the largest sources of radio-frequency interference. Some of the medical devices are especially sensitive to the circuitry used in some of the cellular phones.
In addition electromagnetic compatibility of medical equipment in hospitals has been a matter of concern, since interference from radio-frequency sources can cause medical device or equipment to fail.
The major international standard from the radio-frequency immunity of medical equipment was set in 1993. This standard sets a minimum immunity level of 3 volts per meter. However, other techniques exist that are easily incorporated into the design of electronic systems. This will help to “harden” most medical devices from radio-frequency fields that are much stronger than usual voltage level.
Furthermore, another proposition was made. This proposition calls for minimizing electro-magnetic interference in hospitals. Using only those radio-frequency devices that are sufficiently separated from medical equipment, provided that medical equipment can withstand this type of interference, can do this. Typically, this is calculated using method called free-space propagation, which is only valid in ideal case, and doesn’t always work in real life.
Recently, a study was made using an 800-MHz cellular phone in different rooms and corridors of a hospital. That hospital had both gyprock and clay-block wings. Results were compared to calculations made using free-space propagation method. Results showed that free-space overestimated measured fields of interference in gyprock rooms, and along corridors of both gyprock and clay-block construction. However, the free-space model underestimated field of interference in clay-block rooms, and in below-ground corridors. Therefore administration of hospitals should pay a lot of attention to how hospital buildings were build, and what type of medical equipment is being used in those hospitals.