Wireless Medical Telemetry and EMI
- Suceptibility to EMI
- Digital TV
- Public Health Advisory - Risk of Electromagnetic Interference with Medical Telemetry Systems
- Electromagnetic Compatibility Program
Wireless Medical Telemetry involves a radio-frequency (FR) communication between a transmitter worn by a patient and a central monitoring station. However, the radio or "wireless" link can be susceptible to electromagnetic interference (EMI) from other intentional and unintentional transmitters, resulting in the disruption of medical device function(s).
Such was the case in March 1998 when wireless medical telemetry systems at two hospitals in Dallas, Texas were disrupted by the test broadcast of digital TV (DTV) signals in a frequency band allocated for that purpose. This resulted in a inital FDA Publich Health Advisory and a joint FD/FCC statement:
- FDA Public Health Advisory:Interference Between Digital TV Transmissions and Medical Telemetry Systems
- Joint Statement of the FCC and the FDA Regarding Avoidance of Interference Between Digital Television and Medical Telemetry Devices
Most wireless medical telemetry devices currently operate by transmitting signals in one of two frequency bands: Private Land Mobile Radio Service (PLMRS) frequencies at 450 to 470 MHz, or on vacant TV channels in the range of channel 7 to channel 46. With the advent of DTV, however, there are now fewer vacant TV channels, and DTV signals use more of the frequency spectrum within the channel that they occupy than do analog TV signals. In addition, heavy commercial use of the PLMRS band has lead to changes by the FCC to allow for more users, which could potentially increase the risk of EMI with medical telemetry in these bands. The changes to the PLMRS were adopted in 1995 but were on hold until June 2000, mostly out of concern for EMI with medical telemetry.