The present study demonstrates two new findings in the field of interference by mobile phones on medical equipment.
First, the 2.5-generation mobile communication network GPRS is able to induce a higher rate of EMI incidents than is known for the first-generation network GSM at comparable distances [1
]. Second, the median distance at which EMI incidents caused by new-generation cellular phones take place (3 cm) falls within the '1 meter rule' proposed as a safe distance in patient areas, although the range demonstrated in this study is considerable (0.1 to 500 cm) [1
Studies on EMI by first-generation mobile phones have been based on the GSM network used in Europe, the United States, Australia and part of Asia, or on code-division multiple access (CDMA), which is used mostly in the United States [2
]. Meanwhile GPRS and UMTS networks are used for their advanced properties to transmit video and data wirelessly at a higher speed as well as regular voice telephony [12
Our finding of EMI induced by UMTS with hazardous incidents contrasts with what was demonstrated recently in the only study so far on UMTS by Wallin and colleagues [12
]. No critical UMTS incidents with 76 medical devices were reported besides interference noise on loudspeakers of two ultrasonic Doppler devices. Their only critical incident with GPRS was the total stopping of one infusion pump (out of 12 tested) at a distance of 50 cm. Neither GPRS nor UMTS demonstrated any interference on four intensive care ventilators tested. Three of those ventilators were also tested in our study, and in contrast with those studied by Wallin and colleagues they showed significant and hazardous GRPS incidents and one light UMTS incident. There are two possible explanations for these differences. First, Wallin and colleagues used a different GPRS signal with a frequency of 1,800 MHz and an output power of 1 W, as opposed to 900 MHz and 2 W used in the present study. The lower carrier-wave frequency of the GPRS signal and the corresponding 2 W in our study was chosen for its availability in many continents. GPRS is used worldwide on different frequency bands (900 and 1,800 MHz) in different continents and therefore many 'tri-band or quad-band' mobile phones are sold for their worldwide operation [3
]. Second, the studies differed in their selection from medical equipment available worldwide. Our results apply to the tested devices only as specified, including the year of purchase, and consequently are a limitation of the present study.
Another limitation of this study is the test conditions. The only method for obtaining reproducible results in testing EMI by mobile phones is a standard signal generator to control output power as used in the study by Wallin and colleagues and in our own [3
]. The use of commercially available mobile phones in ringing mode will generate irreproducible results at different locations because mobile phones (GSM, GPRS and UMTS) regulate their output power depending on the nearest cell base station for the telecom provider [4
]. If such a station is nearby, a mobile phone constantly minimizes its required output power, in GPRS to as low as 5 to 10% (50 to 100 mW), to increase its battery lifespan. In our study the output power was controlled and set at the maximum level to mimic a worst-case but realistic scenario. In healthcare facilities the coverage of telecommunication networks could be poor because of its structures and could consequently induce mobile phones to transmit at maximum power, which increases the risk of EMI [1
]. Therefore, as a result of our worst-case scenario it is not to be expected that in daily practice critical EMI incidents with GPRS or UMTS would be more frequent than reported in our study.
Health care applications of new wireless telecommunication technologies are reaching the bedside (namely intelligent pager systems with smart phones, personal digital assistants with internet access, and telemonitoring interhospital intensive care transport) with potential clinical benefits [2
]. However, critical care equipment, with closed loop systems to eliminate human resources and errors, demands permanent technology assessment to ensure its continued performance including electromagnetic compatibility with other devices [2
The international standard on electromagnetic compatibility by the International Electrotechnical Commission in its present form is insufficient to safeguard medical equipment completely from EMI by GSM mobile phones, and our results show that the same holds true for GPRS and UMTS signals [11
]. The present industrial standard lacks stipulations for eliminating EMI in medical equipment. Manufacturers are allowed to comply with the standard by reporting only the distance at which EMI occurs. Reasons why even new medical devices still demonstrate EMI caused by mobile phones would be speculative; examples are complex medical industrial design, rapidly changing telecommunications signals, and costs. This leads one to suspect that the undesirable situation of EMI in the critical care environment will not be eradicated soon.
This study adds to the objective evidence that restrictive use in the critical care environment is sensible without overstressing negligible risks [11