Jan. 9, 2001 ROCHESTER, MINN. — A study by Mayo Clinic researchers found that cellular telephones interfered with the operation of external devices that monitor the heart and lungs, however, in most instances, the interference was not sufficient to meaningfully hinder interpretation of data.
The most severe interference occurred when the cellular telephone was held one to two inches from the most vulnerable area of external cardiopulmonary monitoring devices. Interference of some extent was measured in seven of the 17 devices (41 percent). Among the 526 tests, interference was deemed clinically important in 7.4 percent. Researchers recommend that additional testing be conducted. Clinically important was defined as any interference that might hinder interpretation of data or cause the equipment to malfunction.
"When additional testing is completed, policies regarding cellular phone usage within the hospital environment can be constructed objectively," concluded David L. Hayes, M.D., a Mayo Clinic cardiologist and one of the study's authors.
The banning of cellular telephones within hospitals has not been based on objective experimental or clinical testing, but on theoretical concerns that wireless technology could interfere with medical equipment, the study’s authors said. Considerable research has been done on the potential interactions of wireless technology and implanted devices.
Research on the interaction of the cellular telephone and external equipment in a hospital has been general and inconclusive.
The study appears in the January issue of Mayo Clinic Proceedings.
If a cellular phone is used at some reasonable distance (60 inches in the study) from electrical equipment within the patient’s room or central nursing stations, it is unlikely that any serious malfunction would occur, the researchers hypothesized.
David Herman, M.D., a Mayo Clinic ophthalmologist and John Abenstein, M.D., a Mayo Clinic anesthesiologist, wrote the editorial that accompanies the study’s findings. They write, "it would seem reasonable either to limit or to ban the use of cellular phones in the vicinity of medical electronic devices where patients are particularly vulnerable, such as the intensive care unit and operating unit, until safety of these devices can be reasonably proven." Banning the use of the devices in a patient’s room or procedure area would be a modest precaution, the editorialists wrote.
The Mayo Clinic researchers said cell phone-related interference was seen in the electrocardiographic (ECG) tracings displayed on the physiologic monitor. It occurred at a six to 33-inches from the monitor. If the cellular telephone was held beyond a radius of five feet, these researchers hypothesize ECG interpretation would not be compromised. The most disturbing interference related to cell phones causing a mechanical ventilator to malfunction. Specifically, when the phones were held two inches away from a communication port on the back of the ventilator, the ventilator shut down and restarted.
Digital and analog cellular telephones were tested in the study. Digital phones tended to produce noise on the baseline readings, while analog phones primarily produced movement on the baseline readings of the monitors. Digital phones produced some movement on the baseline.
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