Patient worn telemetry has been around for over thirty years. During this time it has progressed from UHF and VHF to WMTS. Wireless Medical Telemetry Service (WMTS) is a wireless service specifically defined in the United States by the Federal Communications Commission (FCC) for transmission of patients’ health data (biotelemetry).
WMTS was created in 2000 because of interference issues from digital television. The bands defined are 608-614 MHz, 1395-1400 MHz and 1427-1432 MHz. Devices using these bands are typically proprietary. When Welch Allyn in 1999 came out using FHSS (Frequency Hopping Spread Spectrum) in their MicroPaq, this was first shot across the bow against WMTS.
I worked with Welch Allyn (now Hill-Rom) at that time while I was with Symbol, because Welch Allyn used the embedded FHSS radio from Symbol (Symbol, then Motorola, now Zebra). During that time I also completed a prototype of the first WLAN-connected smart infusion pump. The buzz in the industry, both from companies and clinical engineering, was that WMTS was protected and that 802.11 was not safe. In 2005, Integra Systems worked with Dräger to design and implement the first ever real time 802.11 patient monitoring network that was shared with the enterprise shared network. The noise among competitive companies and some in the biomedical community was saying 802.11 is not safe. Now in 2017, all the infusion pump companies have implemented 802.11 in their infusion pumps. About 90% of the patient monitoring companies now have WLAN-enabled patient monitoring and patient-worn telemetry.
When looking at the use of telemetry it is important to understand the requirement for uptime. Patients that are on telemetry tend to be not well and/or have had previous cardiac conditions.
Traditional VHF, UHF, (now all WMTS) system designs have for the most part been uni-directional. There have been some variations on using FHSS in the WMTS bands. Antenna systems for WMTS are based upon coaxial TV infrastructure and used diversity to overcome any nulls. Diversity is essentially two antenna systems, A and B Loss of signal may occur, if you go out of coverage. When this happens, the signal is lost at the central station and of course you have no indication of this loss at the patient’s bedside. If we understand the need for uptime, then it is clear that any loss of signal for a prolonged period of time or episodically could allow an arrhythmia event to be missed. AHA guidelines state that a patient in cardiac arrest must be resuscitated within 10 minutes to avoid any myocardial damage.
802.11 WLAN based patient monitoring and telemetry has major risk avoidance value and the ability to achieve the requirements of high reliability or as they say in the telecommunications industry, the five nines of reliability, 99.999. The following describes the benefits of WLAN-based patient monitoring and telemetry.
Research and Development
WMTS – Limited innovation and proprietary to each company. Legacy technology.
802.11 – Takes advantage of all the major investment of billions of dollars over the past sixteen years.
Only Wi-Fi can provide bi-directional communications. This will now allow for a display on the transmitter.
Quality of Service (QoS)
WMTS has limitations due to channelization, i.e., 25Khz in the 608-614Mhz space.
802.11 patient channels can be considered infinite.
Real-time Spectrum Analysis and Cyber Security Intrusion
Nothing exists regarding WMTS. Companies in the WLAN space have this covered. (See attachments)
Radio Resource Management
Do the transmitters and receivers talk to one another to manage the load on the closed network—they do not.
Today’s enterprise WLAN does this on the fly to manage quality of service based upon the application. (See attachments)
Reducing the Risk via Lack of Signal Coverage
In a traditional VHF/UHF/WMTS design if you move out of signal coverage you will have the network drop its connection. It could also be same with WLAN enabled medical devices. However in the enterprise WLAN space, there are tools available in order to proactively manage the wireless signal strength, thus drastically lowering this potential from occurring. The major benefit of this is that now you have a basic patient monitor on the patient that is monitoring the patient, providing display of the vital signs, and providing control and feedback to the clinician.