The continued evolution of technology appears to have lessened cellular
telephones' electromagnetic interference with medical devices such as monitors
and respirators, a Mayo Clinic study indicates.
Mayo Clinic researchers
have been studying cellular telephone interference with medical equipment for
more than four years.
In their most recent analysis of cellular
telephones and medical equipment, Mayo Clinic researchers report in the October
issue of Mayo Clinic Proceedings that the cellular telephones tested did not
interfere with medical devices that were more than three feet away, marking an
improvement. In the current study, 44 percent of the devices recorded some
interference from the cellular telephones but the vast majority of this
interference should not have had any significance for the
patient.
?Technology changes in both cellular telephones and medical
equipment may continue to mitigate or may worsen clinical-relevant
interference,? says David Hayes, M.D., chair, Division of Cardiovascular
Diseases, Mayo Clinic Rochester and one of the study's authors who has tested
equipment in previous studies. ?Periodic testing of cellular telephones to
determine their effects on medical equipment will be required.?
Health care organizations have reacted
to cell phone interference with a variety of rules. Some ban the use of cellular
telephones on their premises. Others allow cellular telephones to be used
freely. Still others, including Mayo Clinic, ban their use in certain areas:
intensive care units, operating rooms and cardiac catheterization
laboratories.
When the researchers performed this study at Mayo Clinic
Rochester between March 9, 2004, and April 24, 2004, they wanted to determine
whether technology changes by both medical device manufacturers and the cellular
telephone industry have altered the potential for clinical-relevant
electromagnetic interference.
Cellular telephones modulate their power
output based on the strength of the incoming signal. So if the signal is strong,
the power level of the phone is low to conserve battery life. However, if the
signal is weak, the power of the phone increases to ensure reliable
communication. The researchers completed their study of six different telephones
-- Nokia Model 5165 (digital); Sanyo Model SCP-4900 (digital); Nokia Model 3585i
(digital); Motorola Model 205 (digital); Motorola V60 (digital); and Nokia Model
3585i (analog).
Sixteen different medical devices were tested and
interference occurred in seven (44 percent). The researchers conducted 510 tests
by holding the phone next to the devices and then rotating it once a call was
received from a wired telephone. The cellular phones were placed near vulnerable
sites on the device, such as serial ports, cable connection ports and displays.
The farthest distance away that a device
was affected was 32 inches. Most interference occurred with devices that display
electrocardiographic (ECG) or electroencephalographic (EEG) waveforms and
involved noise interference. ECG tracings represent the electrical activity of
the heart, i.e., each heartbeat has a corresponding electrical event and is
represented on the tracing, and the EEG tracing represents electrical activity
of the brain. Two ventilator devices also experienced interference.
Along
with Dr. Hayes, others who conducted the study were: Jeffrey Tri, Rodney
Severson, Allen Firl and John Abenstein, M.D., all of Mayo Clinic.
A
peer-review journal, Mayo Clinic Proceedings publishes original articles and
reviews dealing with clinical and laboratory medicine, clinical research, basic
science research and clinical epidemiology. Mayo Clinic Proceedings is published
monthly by Mayo Foundation for Medical Education and Research as part of its
commitment to the medical education of physicians. The journal has been
published for more than 75 years and has a circulation of 130,000 nationally and
internationally.
Rochester, MN 55902
United States
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