FINAL REPORT TO THE AMERICAN HOSPITAL ASSOCIATION TASKFORCE ON MEDICAL TELEMETRY
W. David Paperman, Texas Children's Hospital
David Pettijohn, Vitalcom, Inc.
Jeffrey Wells, Marquette Medical Systems, Inc
Kevin Schumacher, Marquette Medical Systems, Inc.
Michael Dempsey, Hewlett Packard Company
Robert Snyder, Hewlett Packard Company
Robert Rullman, Spacelabs Medical, Inc.
J. S. Wiley, Spacelabs Medical, Inc.
Donald Witters, FDA (Liaison)
Julius Knapp, FCC (Liaison)
The Spectrum Selection Workgroup was created in response to the potential for interference from digital television transmissions and private land mobile radio operations to patient-connected wireless monitoring. Changes in spectrum use for these two services have created uncertainty and concern to medical telemetry users. To address this concern, this Workgroup's mission was to:
- identify spectrum candidates for future medical telemetry use
- evaluate these candidates against objective criteria
- develop specific recommendations for the American Hospital Association (AHA), that will lead to the implementation of dedicated, exclusive spectrum for medical telemetry needs
Three frequency bands are being recommended for dedicated spectrum allocation for medical telemetry operations. These bands include:
- 608 MHz to 614 MHz (TV channel 37)
- 1385 MHz to 1390 MHz
- 1432 MHz to 1435 MHz
Medical telemetry operation should be considered as "primary" status on these bands, preventing incompatible transmissions from causing unacceptable interference to wireless patient monitoring systems.
These three frequency bands are in addition to present medical telemetry spectrum allocations under 47CFR Part 15 and Part 90 of the Federal Communications Commission (FCC) Rules. Within this frequency spectrum (174 MHz to 216 MHz - TV channels 7 through 13; 460 MHz to 470 MHz; 470 MHz to 668 MHz - TV channels 14 through 46), medical telemetry must still operate, but do so as a "secondary" status user, having to accept potential interference from, and to avoid creating interference to, "primary" status users.
The additional recommendations of this Workgroup are:
- New spectrum allocations for medical telemetry should permit the use of flexible communications technologies (e.g. spectrally efficient modulation schemes, telecommand, non-vital signs data, etc.).
- AHA should serve as a frequency administrator for the medical telemetry industry, and interface with the FCC to alert Hospitals and telemetry equipment manufacturers in advance of new "primary" status spectrum assigned medical telemetry frequencies.
- The AHA Taskforce on Medical Telemetry should file petitions before the FCC to implement these spectrum allocation recommendations.
The use models and technical assumptions documented within this report have attempted to respond to the clinical community's need for expanded deployment of interference-free medical telemetry, while also acknowledging the need to promulgate more spectrally efficient technologies to take advantage of the limited available spectrum. It is acknowledged there may be current or future products that indirectly may be considered "medical telemetry". Efforts have been made to consider the requirements of these communications technologies where possible. However, within the narrow view of addressing the current issue of potential interference from deployment of new broadcast television services and from other consumer and business-related communications devices, emphasis has been placed on patient-connected monitoring applications (real-time communications between the patient, his/her instrumentation, and a centralized monitoring/processing site) within the hospital or a dedicated healthcare facility.
Petitions to implement these recommendations must be promptly filed. To this extent, this Workgroup stands ready and committed to support the efforts of this process to its full completion. The uncertainty regarding the FCC regulatory status of medical telemetry has end-users and manufacturers alike greatly concerned. This uncertainty can be reduced by the submission of well crafted petitions to the FCC and its expedited review in the rulemaking process.
This Workgroup is very grateful to the AHA, FCC, Food and Drug Administration (FDA), National Telecommunications and Information Administration (NTIA), and the many other clinicians, professional societies, and other Workgroups which have contributed to our better understanding of telemetry monitoring and the challenges we all face within the next few years in this important delivery of healthcare information.
Finally, an expression of gratitude must be given to the organizations that employ the members of this Workgroup, without whose support this industry collaboration would not have been possible. The gravity of this issue has transcended corporate boundaries and speaks directly to the issue of public health and safety. In this regard, the spirit of cooperation has been exemplary.
December 4, 1998
1. GOALS FOR MEDICAL TELEMETRY SPECTRUM SELECTION
In attempting to consider spectrum candidates for medical telemetry use, this Workgroup assumed the following goals for guiding its deliberations:
- Dedicated, interference-free, spectrum
Digital television (DTV) services in the VHF spectrum (174 MHz to 216 MHz), and the desired deployment of more spectrally efficient communications devices in the Private Land Mobile Radio portion of the UHF spectrum (450 MHz to 470 MHz) have created two threats to medical telemetry operations. The first threat is the demonstrated potential for disruption of medical telemetry patient monitoring in both frequency bands. The second threat is the limitation of telemetry monitoring growth due to medical telemetry's FCC regulatory status ("secondary") in these bands. There is insufficient spectrum for increases in telemetry channel growth as "primary" users extend their usage of a shared band.
- Spectrum bandwidth to accommodate 1000 telemetry transmitters
The profile of telemetry patient monitoring is changing. While cardiac patients are still the largest segment of monitored patients in telemetry, more acute patients are being monitored, as are the supplemental devices (e.g. ventilators, infusion pumps, etc.) that support them. It has been observed that many hospitals currently have in excess of 300 patient-connected transmitting devices in use at one time. Initial surveys have indicated that within 10 years, medium to large hospitals will use 1000 patient-connected transmitting devices. With this increase in acute patient monitoring, other vital signs measurements, in addition to ECG, will be added to medical telemetry. Accordingly, this additional telemetered patient data will require suitable spectrum bandwidth for present and future patient populations. The mission critical nature of this increased patient data underscores the requirement that a spectrum candidate be dedicated, exclusive, and free of potential interference.
- Flexible spectrum allocation to accommodate different applications
Clinical users will drive different applications for medical telemetry. Hospitals will use technology to reduce risk to patients through more applicable and efficient monitoring, and to contain costs of healthcare delivery, while improving the quality of patient outcomes through better diagnostic and monitoring data. Any spectrum candidate for medical telemetry must therefore be flexible enough in its technical and FCC regulatory attributes to support, rather than limit, the different types of communications applications that can meet the end-user's goals.
- Ease of transition to new spectrum for existing telemetry users
Some consulting firms have estimated the value of medical telemetry equipment installed in U. S. Hospitals to be in excess of $100 million. The ASHE survey of some 500 hospitals shows the median age of this equipment to be approximately 3.5 years; the mode is 1 year. Given a depreciation period of 10 years for this type of equipment, it is clear that transition to another frequency could be very costly to hospitals. The only way to avoid this cost is to extend the transition period of these new bands and choose the new bands in such a way as to allow some salvage of the hospital's basic investment.
2.TECHNICAL REQUIREMENTS FOR MEDICAL TELEMETRY SPECTRUM SELECTION
Five major technical requirements were established for use in selecting appropriate spectrum candidates. These requirements reflected the themes outlined in the goals above and provided a framework for comparing spectrum candidates.
- Communications Reliability
The proposed spectrum must not have in-band or adjacent band users that create interference to medical telemetry operations. Medical telemetry monitoring is performed 24 hours a day, and cannot tolerate interference. Decisions, ranging from patient treatment choices to immediate care interventions, can be compromised by an unreliable communications link. The desired spectrum candidate must offer the expectation that the possibility of interference will be remote.
- Spectrum Attributes
Spectrum attributes considered include the amount of available bandwidth, its contiguity, and the suitability to support multiple modulation and transmission schemes for spectral efficiency and frequency re-use. Further consideration was given to domestic and international allocation status.
- Propagation Characteristics
The physical transmission path loss (the attenuation of the radiated telemetry signal through the air and the physical structures within the hospital) of the proposed spectrum candidate was evaluated relative to the current predicate medical telemetry bands. The noise floors (the level of other undesired signals from atmospheric, space, or man-made sources, from which the desired telemetry radio signal must be extracted by the telemetry receiver) and susceptibility to multi-path fading (the propagation properties of two or more electromagnetic waves from the same telemetry transmitter that interfere with each other to attenuate the desired signal at the telemetry receiver) were also reviewed. These characteristics have direct impact on recurring cost of ownership (e.g. battery costs) and initial installation and equipment costs (e.g. upgrade/migration feasibility, antenna system deployment, receiver complexity).
- Safety Considerations
This requirement took into account the amount of RF radiated power that the patient, as well as other sensitive medical instrumentation would be exposed to. In general, the higher the operating frequency, the more radiated power is required to overcome additional path loss.
Specifically, the Workgroup reviewed ANSI/IEEE C95.1-1992 for the maximum permissible partial body exposure allowed for an uncontrolled environment. In order for the proposed spectrum solution to meet this requirement, the energy that, in the transmitter in the proposed spectrum solution would need to radiate, must be lower than the C95.1 limit.
The Workgroup also examined the potential for each of the proposed spectrum candidates to require telemetry products to generate field strengths in excess of 3 volts per meter (refer to the international electromagnetic susceptibility standard of EN60601-1-2). These fields could create possible electromagnetic interference to other medical devices.
- Product Implementation Considerations
The final requirement is the availability of commercial RF components and low cost field support instrumentation. This is required to bring new product to market in a timely fashion, and to facilitate the site survey/installation process.
3. WORKGROUP INPUTS
The Spectrum Selection Workgroup obtained input from the liaison organizations (FCC, FDA, NTIA); informal discussions with members of the wireless local area network (LAN) and radio astronomy communities, and other Workgroups chartered by the AHA Taskforce.
- Definition of Medical Telemetry
Using the definition that "…wireless medical telemetry is the measurement and recording of physiological parameters and other patient-related information via radiated bi or unidirectional electromagnetic signals contained within a healthcare facility or extending beyond to other buildings and locations…", this workgroup focused the spectrum selection process on real-time communications between the patient, his/her instrumentation, and a centralized monitoring/processing site. Other communications devices (e.g. pagers, etc.) used within a healthcare facility not directly meeting this definition were not considered as part of this spectrum selection process.
- Parameter Use Models
The Clinical Parameters Workgroup developed a model for monitored parameter usage and duration by conducting a survey. The survey was administered to geographically dispersed hospital administrators, biomedical engineering directors, principal clinicians responsible for medical telemetry, and clinical professional organizations. Repeated below is a summary of the results from this survey.
CURRENT TELEMETRY MONITORING NEEDS Physiologic Parameter Concurrent Patients adult electrocardiogram 200 - 600 pulse oximetry 16 - 210 obstetrical (fetal/maternal) parameters 0 - 150 invasive pressures 17 - 420 respirations 4 - 210 12 sets of parametric data up to 500 patients Physiologic Parameter Concurrent Use Model Number of Concurrent Waveforms Required Bandwidth Electrocardiogram 500 3 4.000 MHz Pulse oximetry 250 1 0.150 MHz Obstetrical parameters 100 3 1.300 MHz Invasive pressures 300 2 0.400 MHz Respirations 100 1 0.025 MHz 12 sets of parametric data 500 0 0.250 MHz TOTAL 6.125 MHz
This use model is based on the assumption of 500 concurrently operating telemetry transmitters today, and a 0.8 bit per second per Hertz spectral efficiency metric currently recommended by FCC (see 47CFR 90.203, Section 3). This results in a spectrum bandwith requirement of 6.1 MHz (note that nearly 10 MHz is in use today for 25 kHz channelized telemetry units in the UHF band, and approximately 12 MHz in use for 100 kHz channelized telemetry units in the VHF band). This amount of spectrum is expected to double to more than 12 MHz if one considers a growth in 5 to 10 years to 1000 telemetry transmitters. Thus, a potential spectrum band candidate must have at least 6 MHz in available bandwidth.
- Spectrum Candidates
The following frequency bands (MHz) were considered for use for medical telemetry operations:
- 174 - 216
- 216 - 220
- 328 - 335
- 402 - 406
- 450 - 470
- 470 - 668
- 608 - 614
- 746 - 806
- 902 - 908
- 1385 - 1390
- 1432 -1435
- 2385 - 2390
- 2390 - 2400
- 3650 - 3700
4. EVALUATION OF SPECTRUM CANDIDATES
The attached spreadsheet below summarizes the evaluation on the final spectrum candidates. Earlier candidates were dismissed due to their potential for in-band/adjacent band interference; inadequate bandwidth; their current FCC regulatory status; undesirable path loss and power requirements; or limited merchant market support for off-the-shelf RF components.
Band in Question
Cost of Ownership
Disposable cost (batteries, etc.)
Cost of migration of any current users