GlucoseSensor

Government documents are a great way to get an insiders view of several industries, and health care is no exception. This FCC Request for Waiver document is a gold mine of information. In this Request, DexCom asks for a waiver to the Medical Implant Communications Service (MICS) rules. (You can read my post on the product in question here.) We learn about the FCC's attitudes towards MICS, a lot about DecCom's product, and learn who opposed and supported the waiver before the FCC.

The reason for the Request fror Waiver was that DexCom did not want to comply with all the requirements of MICS. In short, they felt that fully supporting MICS would increase the size of their implants and impact battery life to an unacceptable degree, and add too much cost to the product.

The implantable blood glucose monitoring sensors come in two flavors, STS (short term - injectible probe that is replaced every several days) and LTS (long term - a fully implanted unit that lists up to 1 year). They will operate on only one frequency 402.142 MHz +/-40 kHz), using only 120 kHz of bandwidth. The power will be -20dBm conducted, less than that permitted in the MICS band. The sensors will broadcast for only 6-9 milliseconds every 5 minutes. DexCom stated that the combination of bandwidth, power and duration make the likelihood of causing interference virtually nil - an argument the FCC agreed with. The close proximity of the patient carried receiver with the implanted sensors make it unlikely that another MICS device will interfere with the DexCom device during data communications.

Of course the way things should work in theory and what happens in the real world are frequently different. To ensure patient safety accommodations must be made for potential failures. Here's what DexCom worked out for interference. If interference were to cause the loss of a set of data, one of 288 per day, the loss of any one data set would not be critical. The DexCom system is not a life critical patient monitor; instead, it provides a tighter feedback loop between blood glucose levels and a patient's diet or use of insulin. To delay the display of a reading (even one that's out of range) by 5, 10 or even 15 minutes would still be an improvement over current blood glucose monitoring techniques. Not a particularly sexy technical solution, but one that is reasonable.

So who supported and objected to this waiver? The waiver was supported by DexCom's chip vendor AMI Semiconductor, and more surprisingly, Biotronik.  The sole party opposing the waiver request was bare-knuckle competitor Medtronic. (You can read a profile on Medtronic here.) Of course, Medtronic makes a variety of implantable medical devices, many of which are wireless, some of which use MICS; they are a direct competitor to DexCom. They objected that because the STS transmitter lies outside the body, it did not qualify for use in MICS. Medtronic also complains that DexCom does not disclose, "key RF system operating parameters, or [...] a complete description of its sensor systems," thus making it impossible to fully assess interference potential. Medtronic also contended that the waiver was unnecessary because other spectrum was available that would permit it to operate with in the FCC's rules. They suggested the FCC limit their waiver to just 2 years and require DexCom notify physicians and patients of the potential for interference. It seems that Medtronic also opposed a waiver request for the Biotronik Philos DR-T, on the basis that the periodic operation of the device without LBT functionality violates the MICS rules.

The FCC did not buy any of Medtronic's arguments for denying the waiver. The FCC issued the waiver, making it dependent on the timing and outcome of any relevant rule making they may conclude, with a minimum of three years as a reasonable timeframe for successfully marketing and implementing use of the devices in their current configuration. Based on this waiver and the previous waiver for Biotronic, the FCC acknowledged that they may need to revise their rules for MICS to accommodate other technical solutions that are consistent with the goals for MICS - new more effective medical implant technologies that are assured to offer very low levels of potential interference.