Newswise — 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. Copies of the articles are available online at

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Mayo Clinic Proceedings (Oct-2005)