Medical Telemetry: Then and Now
Associate Director, Health Devices Group
May 24, 2006
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- Capable of providing ECG monitoring only
- Narrowband transmission - Fixed frequency, 25 or 50 kHz channel spacing
- Unidirectional: From transmitter to receiver
- 2 bands available:
- Very High Frequency/Ultra High Frequency Television (VHF/UHF TV)
- PLMR (Private Land Mobile Radio)
VHF/UHF TV Telemetry
- Operation in frequencies:
- 174 – 216 MHz (TV channels 7 – 13)
- 470 – 608 MHz (TV channels 14 – 36)
- 614 – 668 MHz (TV channels 38 – 46)
- Medical telemetry operates within unused TV channels
VHF/UHF TV Telemetry
So … What’s the Problem?
The Dallas Incident
- Telemetry systems at Baylor Medical Center and Dallas Methodist Hospital operated within previously unused TV channel 9
- Late February/Early March 1998 – telemetry systems at both hospitals stopped working (blanked out)
- Discovered that local TV station WFAA had started broadcasting digital TV on channel 9
- March 25, 1998 - Joint Statement issued by FCC and FDA regarding avoidance of interference between digital television and medical telemetry devices
The Dallas Incident
What Does the Future Hold for VHF/UHF TV Telemetry?
- Continued use of telemetry in these frequencies is possible
- Careful planning and establishing open lines of communication with local TV stations are required
- Resources for planning include:
Private Land Mobile Radio (PLMR) Telemetry
- Operation in frequencies: 450 – 470 MHz
- Medical telemetry operates in between PLMR channels
- PLMR channels spaced 25 kHz apart and medical telemetry spaced 12.5 kHz from PLMR channels
- Refarming of PLMR channels - 25 kHz to 6.25 kHz spacing
- 450 – 460 MHz began in 2001
- 460 – 470 MHz began in Jan. 2006
PLMR Telemetry – Before Refarming
PLMR Telemetry – After Refarming
What Does the Future Hold for PLMR Telemetry?
- Continued use can be risky!
- PLMR transmissions are mobile (taxis, delivery trucks, police, ambulance, etc)
- PLMR transmissions are much stronger than medical telemetry (2+ watts vs. 20 mW)
- No reliable method to predict when interference can occur
- ECG and pulse oximetry and noninvasive blood pressure now available
- Narrowband and spread spectrum (direct sequence, frequency hopping) transmission
- Uni-directional and bi-directional transmission
- Blurring between telemetry and small, portable monitors (as small as 2 lbs)
- 4 bands available:
- VHF/UHF TV
- Wireless Medical Telemetry Service (WMTS)
- Industrial, Scientific, and Medical (ISM)
Wireless Medical Telemetry Service (WMTS)
- Created in October 2000
- Operation in frequencies:
- 608 – 614 MHz (channel 37)
- 1395 – 1400 MHz
- 1427 – 1429.5 MHz*
- Medical telemetry operates as co-primary user in these frequencies (with radio astronomy, Govt. operations)
- Registration process with American Society for Healthcare Engineering (ASHE) to ensure coordination of frequency use
- Many intricacies involved with use of medical telemetry in this band
* Frequencies of operation change to 1429 – 1431.5 MHz for 7 locations
Industrial, Scientific, and Medical (ISM)
- Uses cross-industry standard wireless protocols (e.g., IEEE 802.11 family of standards – 802.11a, b, g, FH)
- Use is not specific to medical telemetry
- Requires hospital to coordinate inter-operability between telemetry system and other wireless systems (e.g., wireless LAN)
What is Everyone Else Doing?
- Medical telemetry has undergone significant change over the past few years
- Now, more than ever before, healthcare facilities need to be proactive in determining the risk of interference to their medical telemetry operations
- There is no one answer to “What is the best frequency to use for medical telemetry?” - it depends on the specific circumstances at your facility
Resources From ECRI
ECRI, Health Devices:
- “Medical Telemetry is on the Move: Is it Time for You to Change Frequencies?”, June 2002, p. 217-222
- “Ambulatory Telemetry Systems” [Evaluation], Sept 2002, p. 313-331
- “Trends in Physiologic Monitoring Systems: The Old and The New”, Oct 2004, p. 345-353
- “Physiologic Monitoring Systems” [Evaluation], Jan 2005, p. 5-45
Let me introduce our first speaker - his name is Richard Diefes and he’s Associate Director of the Health Devices Group at ECRI.
Rich has been with ECRI since 1995 and has conducted a number of projects on wireless technologies and monitoring systems. He has been the project lead for several comparative evaluations of physiologic monitoring systems which were published in ECRI’s Health Devices Journal. Mr. Diefes has also been the principal investigator on many problem reports submitted to ECRI involving monitoring devices and use of wireless technology.
In support of ECRI’s Accident and Forensic Investigation Group, he has served as the lead investigator in greater than a dozen cases and has provided expert testimony related to his forensic investigation work.
And as I’ve said, the title of this presentation is Overview of Medical Telemetry and it’s basic enough for those who are not intimately involved in this area. But if you do have questions, please write those down and we will have a brief period after his presentation for you to ask those questions.
Okay, go ahead, Rich.
Richard Diefes: All right.
Well, thank you very much, Terrie. I appreciate the opportunity to speak today. And to get things started, I’d like to focus on the evolution of medical telemetry over the past few years, giving some discussion on where we’ve come from and where we are currently with medical telemetry.
Moving on to Slide 2, I’d first like to start out by briefly discussing who ECRI is for those of you who may be unfamiliar with us.
ECRI is a nonprofit health research agency whose mission it is to promote the highest standards of safety, quality, and cost effectiveness in healthcare to benefit patient care through research, publishing, education, and consultation.
To this end, ECRI provides a number of different services that include technology decision making to help healthcare facilities plan and make the right decision for investing in technology for the future; supply chain support to provide guidance and recommendations for which products will best meet the needs of a healthcare facility; quality in patient safety to inform healthcare facilities about hazards and recalls, provide tools in risk management, and investigate problem reports; and finally, information analysis and delivery in support of clearinghouses such as the National Guideline Clearinghouse and the National Quality Measures Clearinghouse.
Let’s move on the graphic on Slide 3.
First of all, let’s start out by defining what we mean by medical telemetry.
We’re referring to the patients wearing telepacks or transmitters that are most typically used to monitor ECG, although monitoring of pulse oximetry as well is also becoming more common. These telepacks or transmitters wirelessly send data to an antenna network which in turn, sends the data to a central station monitor. The central station then displays the ECG waveforms of the patients on telemetry and issues alarms to inform staff about clinically significant events. In the traditional sense, each transmitter sends its data out on a different frequency so that the transmitters don’t interfere with each other.
Turning to Slide 4, if we go back a few years to the mid to late ‘90s telemetry packs were for the most part, only capable of providing ECG monitoring. In addition, the only type of transmission available for the telepack was narrow band transmission. And what this means is that each telepack was set to specific frequency or channel and each channel is spaced usually 25 or 50 kilohertz away from adjacent channels. This transmission was unidirectional, meaning that the signal is sent from a telepack to the central station, but there’s no way for the central station to communicate back to the telepack. As a result, if signal loss were to occur during transmission from the telepack to the central station, there was no way for the central station to communicate this back to the telepack and request that the telepack resend the lost data.
Back then there were two frequency bands that were available, VHF/UHF television and private land mobile radio.
If we move on to Slide 5, we could start out talking about the VHF/UHF TV telemetry band. These bands cover frequencies in the range 174 to 216 megahertz corresponding to TV channels 7 to 13. They also cover 470 to 608 megahertz corresponding to TV channels 14 to 36. And finally, 614 to 668 megahertz corresponding to TV channels 38 to 46.
Notice that I skipped over Channel 37. This channel has been reserved for use by radio astronomy so that no TV broadcast is permitted on this channel. I will bring up Channel 37 again as it relates to telemetry later on in my talk.
The way that medical telemetry works in these bands is that the telepacks are set to transmit on frequencies corresponding to unused TV channels.
Let’s take a look at this on the next slide.
In this example, TV Channel 8, the green box, and TV Channel 10, the red box, represent two broadcasting TV channels. To avoid these two broadcasting TV channels, medical telemetry is set up to operate on the frequencies corresponding to the unused TV Channel 9. Each yellow bar represents transmission from a single telepack. Keep in mind that the actual TV channels in use will vary with geographic location.
FCC provides an online tool that you can use to help determine all the TV broadcasts in your area and I’ll get back to this tool in a few slides.
So if telemetry is set up to avoid broadcasting TV channels then what’s the big deal? Why not just continue to keep avoiding TV channels that are being used? Well the answer is on Slide 7, digital television.
Digital TV is now filling in some of those unused TV channels, literally squeezing medical telemetry out of the picture.
To illustrate how digital television has impacted the use of telemetry let’s go back a few years to an incident that occurred in Dallas, Texas as described on the next slide.
Keeping with the design to use medical telemetry in unused TV channels both Baylor Medical Center and Dallas Methodist Hospital have set up telemetry to operate on frequencies within TV Channel 9. The systems were operating normally until late February 1998 when all of a sudden, signals from a number of telepacks were no longer being displayed at the central station; they just blanked out.
It was discovered that local TV station WFAA had just started broadcasting digital TV on Channel 9. Unfortunately, because there was no communication between the TV station and the hospitals, the fact that the hospitals’ medical telemetry and the TV broadcast were operating on the same frequencies wasn’t discovered until it was too late.
Fortunately however, this incident quickly got the attention of both the FCC and FDA and on March 25, 1998, FCC and FDA issued a joint statement to warn both the healthcare and television broadcast communities about the potential interference.
As we look at the graphic on Slide 9, we see that the hospital had chosen to set their telepacks to operate on frequencies in unused TV Channel 9 to avoid the TV broadcast on Channel 8. Unfortunately, they weren’t aware that the new digital TV broadcast was going to launch on Channel 9.
Turning to Slide 10, the question is what does this all mean for future use of medical telemetry in these TV bands? Bottom line is continued use of telemetry in these frequencies is possible.
Careful planning and establishing open lines of communication with local TV stations will allow healthcare facilities to define the risk of interference from TV broadcasts and plan accordingly.
The risk of interference can be fairly well-defined in this case because TV station broadcasts do not move around and they operate on well-defined frequencies. In addition, new digital TV broadcasts are well-documented and can be planned for prior to going live.
While continued operation of telemetry in the TV bands is possible, use of these frequencies for new telemetry systems is not an option since medical telemetry suppliers no longer produce new telemetry products operating in these bands.
As I mentioned back on Slide 6, the FCC provides a very useful tool that can be used to define the TV broadcasts in your area, the FCC TV Database Query. This query allows you to enter your location, city and state, and provides a list of TV broadcasts in your area. Additional links provide maps of broadcast coverage areas so that you can see where your facility is situated relative to a TV station’s broadcast coverage area.
Another FCC site to check out is the Low Power TV site.
Moving on to Slide 11, let’s turn to the second band that was available for medical telemetry use, the private land mobile radio band. This band covers frequencies from 450 to 470 megahertz. Note that TV does not broadcast on these frequencies. So digital TV doesn’t have a direct impact on telemetry in this band.
The way that medical telemetry works in the PLMR band is that medical telemetry operates in between PLMR channels. PLMR channels are spaced 25 kilohertz apart and medical telemetry channels are all set 12.5 kilohertz from a PLMR channel.
And this all changed when FCC started refarming PLMR channels so that instead of a channel being spaced 25 kilohertz apart, they were now being moved so that the channels were spaced only 6.25 kilohertz apart. This would allow more PLMR channels to be used in a given area. Unfortunately for healthcare, this means that once again medical telemetry is getting squeezed out.
This refarming of tighter PLMR channels began in 2001 for the 450 to 460 megahertz band and just began in January of this year for the 460 to 470 megahertz band.
Slide 12 shows how PLMR channels and medical telemetry worked before the refarming.
Medical telemetry is represented by the yellow bars and PLMR by the red bars. Note the spacing of 12.5 kilohertz between the medical telemetry and PLMR to avoid interference between the two.
If we turn to Slide 13, this shows what happens after refarming.
PLMR can now lie directly on medical telemetry frequencies. In addition, adjacent PLMR channels can also be only spaced 6.25 kilohertz away from a medical telemetry channel which may not be sufficient to avoid interference.
Turning to Slide 14, what does the -- what does the future hold for medical telemetry in this band? The bottom line is continued use can be risky.
Unlike medical telemetry in a TV band, medical telemetry in the PLMR band is competing with transmissions that are mobile. PLMR is used by taxis, delivery trucks, police, ambulance -- all of which are coming and going from healthcare facilities all the time.
In addition, these PLMR transmissions are also much stronger than medical telemetry signals on the order of 2 watts or more compared to only about 20 milliwatts. There really is no reliable way to predict when interference can occur -- how will you know whether that taxi driving up to your hospital is using PLMR on the same frequency that one of your telepacks is using?
In addition, FDA has been recommending for the past several years, most recently in November of 2005, that healthcare facilities migrate their medical telemetry out of the PLMR bands.
As stated in the November 2005 public health notification, according to tests conducted by FDA, the transmitters operating under new licenses in this frequency band can interfere with medical telemetry systems. This could lead to lapses in patient monitoring and missed alarm events -- putting patients at risk.
The anticipated interference will not be limited to urban areas. Any medical facility in the vicinity of mobile radio could be affected.
Moving on to Slide 15, over the past several years, telemetry has evolved in many ways. Instead of simply providing only ECG monitoring, today’s devices can provide both pulse oximetry and non-invasive blood pressure monitoring using patient-worn devices.
In addition to narrow band transmission, today’s telepacks are capable of spread-spectrum transmissions such as frequency hopping in direct sequence. Spread-spectrum transmissions allow those signals to be spread over a wide range of frequencies as opposed to the fixed frequency narrow band devices.
Some telepacks are also capable of supporting bidirectional transmissions, allowing communication both to and from a central station. These are bidirectional along with spread-spectrum transmissions and can allow for more robust communication between a telepack and a central station.
Bidirectional communication can permit the resending of lost data. And spread-spectrum transmission can be less susceptible to interfering signals than narrow band transmissions.
Another change that has occurred is that the difference between telepacks and small portable monitors has blurred as portable monitors continue to shrink in size, some being as small as 2 pounds.
Continuing on with the changes that have occurred with telemetry, on Slide 16, we see that in addition to medical telemetry in the TV and PLMR band, medical telemetry is now also available on two additional bands -- the wireless medical telemetry service or WMTS and the industrial scientific and medical band or ISM.
Let’s start out with WMTS on Slide 17.
It was created in October of 2000 largely as a result of the Dallas incident in 1998. WMTS actually covers three frequency ranges -- 608 to 614 megahertz, this range corresponds to TV Channel 37 which is the channel that we skipped over in the discussion of telemetry in the TV bands; the upper WMTS band includes 1395 to 1400 megahertz and 1427 to 1429.5 megahertz. Notice that in this last frequency range, the frequencies of operation changed to 1429 to 1431.5 megahertz for seven localities.
Medical telemetry operates as a co-primary user in these frequencies along with radio astronomy and government operations. Because of this, there may be some restrictions on use of some WMTS frequencies depending on location.
Registration for use of WMTS telemetry with the American Society for Healthcare Engineering or ASHE insures coordination of frequency use.
As you can see, there are a number of intricacies involved with the use of medical telemetry in this band.
Let’s turn to the next slide covering the other band available for medical telemetry, the ISM band.
ISM telemetry uses cross industry standard wireless protocols such as IEEE 802.11 family of standards, including 802.11a, 802.11b, 802.11g and frequency hopping.
Use of the ISM band is not specific to medical telemetry; many different wireless devices such as laptops and portable phones use the ISM band. As such, this requires that a hospital coordinates interoperability between its telemetry systems and other wireless systems such as the wireless local area network.
With these four bands now available for medical telemetry use, ECRI was interested in seeing the breakdown of what bands hospitals were using and we conducted an online poll at our Web site in January of this year asking the question: What band does your system use? And the poll results are presented on Slide 19. And while our poll doesn’t represent a comprehensive review of all hospitals, it does reveal some interesting results.
Not too surprising WMTS is the most common band to use for medical telemetry. What is a bit surprising is that the second most common band is PLMR telemetry which is, as we discussed, becoming riskier to use in light of the refarming of PLMR and the granting of additional PLMR licenses at the start of this year.
Looking over the results of the poll that Terrie just went over for this audio conference, we see that WMTS as well came up as the most common band in use. However, unlike the ECRI poll, the TV band, and not the PLMR band is the second most common band in use. And this may reflect that hospitals are moving out of the PLMR band as the year progresses.
In conclusion, there certainly have been a number of significant changes to medical telemetry over the past few years, and now more than ever before, we need to be proactive in determining the risk of interference to your medical telemetry operations. The bottom line is there is no simple answer to what is the best frequency to use for medical telemetry, rather it will depend on the specific circumstances at your facility and each facility will need to do their homework to determine which approach will work best for them.
And on Slide 21, I’ve listed a few articles from our Health Devices journal for reference.