The air is buzzing with talk about wireless technology for patient monitoring. Two distinct approaches are emerging and they are vying for your dollars. Should you join the WMTS bandwagon or follow the ISM boosters? And what the heck do these initials stand for, anyway? We give two major candidates an opportunity to sway the biomedical electorate, and we’ve outlawed punch card ballots.
Confused about what’s happening in the world of medical telemetry and wireless patient monitoring? At local levels, there’s been an ugly show of negative campaigning by radio frequency partisans. • In order to bring clarity to this debate, we invited two statesmen of patient monitoring’s parties to address biomedical voters on behalf of the leading candidates vying to replace existing telemetry strategies and dominate new patient monitoring installations. • Starting on this page, nominating the use of wireless networking protocols operating in the Industrial, Scientific and Medical (ISM) radio bands, we have Jim Welch, CCE, the Chief Technology Officer of Welch Allyn Monitoring. • Addressing us from the next page, speaking on behalf of the recently-established Wireless Medical Telemetry Service (WMTS), we have Mark Kotfila, a Philips Medical Systems engineer responsible for a raft of patents that improved patient monitoring telemetry. • ISM or WMTS? Decide which works for you.
In March 2001, Welch Allyn Protocol introduced the first patient-wearable multiparameter monitor, the MicroPaq. Weighing less than one pound, with a display and alarms, and powered by a rechargeable battery, the MicroPaq uses the wireless FlexNet to connect with Acuity central stations, creating an innovative approach to monitoring ambulating patients.
The wireless network technology chosen for FlexNet is IEEE 802.11 compliant, 2.4 GHz radio. Radiators in this spectrum are required to use spread spectrum modulation, a method originally developed by the military for communications in high-interference field applications. FlexNet employs frequency hopping spread spectrum (FHSS). Embedded in the MicroPaq is a radio transceiver that communicates bi-directionally with a wireless access point (AP) capable of supporting up to 15 MicroPaqs. The AP and MicroPaq coordinate a pseudorandom frequency hopping pattern across 79 defined channels in the 83 MHz of available spectrum. The hopping feature allows the MicroPaq to dynamically avoid interference sources, as well as coexist with other devices sharing the spectrum.
FlexNet is designed for monitoring every patient on every nursing unit in the hospital by dynamically reusing the available spectrum. There are no dedicated frequency channels since each wireless device negotiates its hopping sequence with the AP at the time of initial connection. Tests performed on large installations show packet loss (drop-out) rates of 0.02 percent, a 100-fold improvement over traditional one-way telemetry systems.
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