Cellular Phone Interference With the Operation of Mechanical Ventilators

Cheryl I. Shaw; Robert M. Kacmarek; Rickey L. Hampton; Vincent Riggi; Ashraf El Masry; Jeffrey B. Cooper; William E. Hurford


Crit Care Med. 2004;32(4) 

In This Article

Materials and Methods

A Nokia 6120i (TDMA, 800-900 MHz) cellular phone and Nokia computer applications were used to provide and control the output power of the cellular phone. This phone, similar to other cellular phones on the market, was chosen because we were able to computer control the transmission variables: frequency, power, and modulation. All 14 ventilators tested ( Table 1 ) were powered by an Aridyne 2000 Compressor (Timeter Instrumentation, St. Louis, MO) and ventilated a rubber 1.0-L test lung. All adult ICU ventilators were set in volume assist/control mode; tidal volume, 400 mL; set rate, 15; inspiratory to expiratory ratio, 1:2; Fio2, 0.21; positive end-expiratory pressure (PEEP), 5 cm H2O; and sensitivity at the manufacturer's recommended default setting. The bilevel pressure ventilators, the Respironics ST-D 30 and Vision ventilators, were set in the pressure assist/control mode (spontaneous/timed); peak pressure, 20 cm H2O; PEEP, 5 cm H2O; Fio2, 0.21; inspiratory time, 1 sec; and rate, 15/min. The infant ventilators, Bird VIP and Drager Evita, were set in the pressure assist/control mode; peak pressure, 20 cm H2O; PEEP, 5 cm H2O; rate, 25/min; inspiratory time, 0.4 secs; Fio2, 0.21; and sensitivity at the manufacturer's default setting. The Sensormedics 3100 oscillator only operates in the control (does not allow patient triggering) mode and was set as follows: rate, 15 Hz; bias flow, 20 L/min; mean air pressure, 15 cm H2O; percent inspiratory time, 33%; and delta pressure change, 40 cm H2O. A spectrum analyzer (Agilent E4407B ESA-E, Palo Alto, CA) was used to characterize the electromagnetic spectrum in the test area and to verify cellular phone power output. All devices and testing components were inspected for proper function before and after the EMI testing. In addition, all electronic test equipment were also tested for EMI caused by the cellular phone. None of the testing equipment malfunctioned as a result of RF interference.

The cellular phone frequency was set to 828.750 MHz (channel 125), analog modulation, and the power output was set at each of the following: 16, 40, 100, 250, and 600 mW. The cellular phone was set to broadcast back to a cell tower. The spectrum analyzer confirmed the relative power output and frequency. The frequency chosen, one of many used by cellular phones, did not disrupt the local cellular network.

The testing room (18 × 19 feet) was located in the subbasement of the hospital. During testing, the devices were located in the center of the room. A spectrum analyzer was used to monitor the electromagnetic spectrum to ensure that the test phone was the only source of radio frequency energy.

The American National Standard Recommended Practice for On-Site Ad Hoc Testing.[7] was used as a guideline for our testing protocol. For the initial test, the cellular phone was powered to 600 mW and rotated in the x, y, and z-axes approximately 100 cm from the floor and 100 cm from the device. Testing was repeated with the cellular phone positioned 100 cm from the floor and 30 cm from the device and the phone power output set sequentially at 16, 40, 100, 250, and 600 mW. We also tested the effects of RF energy 15 cm and ≤3 cm from the device. If we observed interference caused by RF energy with the cellular phone held away from the tester's body, testing was repeated with the cellular phone placed in the tester's hip pocket.