If you're going to the hospital, you may want to leave your cell phone at home. According to the results of a study that appears in the January issue of the Mayo Clinic Proceedings, cellular phones interfere with the operation of external monitoring devices for the heart and lungs. For the most part, interference was not "clinically important"--that is, it didn't hinder interpretation of the data or cause equipment to malfunction. But the researchers did detect interference in 41 percent of the 17 cardiopulmonary monitoring devices tested, and among the 526 tests, 7.4 percent were considered clinically important.

The most interference occurred when the phone was held one to two inches from the most sensitive part of the monitoring device. In one alarming instance, phones held two inches away from a communication port on the back of a mechanical ventilator caused the ventilator to shut down and restart. The team also observed cell phone-related interference in the electrocardiograph tracings displayed on monitors. Maintaining a distance of about 60 inches between phones and monitoring devices, the researchers offered, would probably be sufficient to avoid equipment malfunction.

"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," David Herman and John Abenstein of the Mayo Clinic write in an accompanying editorial. And considering the distance at which interference occurred, they add, banning cell phone use in a patient's room or procedure area would be a modest precaution.