Are your Wireless Medical Devices up to the Coexistence challenge?

August 26, 2011 - 1 Comment

An interesting article titled “Wireless Medical Device Coexistence” (found here) was passed my way recently.  The article made a case that by creating a formalized testing strategy the risks associated with the coexistence of wireless technologies could be reduced resulting in a safe and effective wireless medical device. After reading it – I began to consider the problems we all face with wireless device coexistence and began to ask myself if such testing would improve the coexistence challenge.

Many medical devices today include wireless interfaces that utilize 802.11, Bluetooth or even ZigBee all within the ISM (Industrial, Scientific and Medical) band.  The criticality of such connectivity varies widely across the various medical device types that exist.  The most critical of these devices require continuous wireless connectivity with a “zero or near zero” packet loss factor.

The paper points out that the IEC-60601-1-2 is the standard used for EMC (Electromagnetic Compatibility) testing of medical devices, but the standard does not include testing recommendations to determine the conditions necessary to maintain a wireless connection when subject to interference.  Now some of you Biomedical and Clinical Engineers might point to the ISO-14971:2007 standard, but this is focused on identifying the risks during the product lifecycle and does not specifically address the RF aspects.

So I wonder, if the industry created a testing standard for medical device coexistence (in the ISM band), would this advance our cause and allow more of us to get a better night sleep?  The article provides some examples of a suggested testing strategy (you can read it here), and I won’t debate the finer points but have to ask if this would result in a safer and more effective medical device.

The overall goal then is to design wireless medical devices that are less susceptible to interference caused by coexistence – we all concur on this being a beneficial goal.   The ISM band(s) by FCC definition requires that receivers operating within the band tolerate interference of other transmitters within the same band.  Within a typical healthcare environment however, there are NUMEROUS examples of ISM devices in use.  Oh off the top of my head I can think of Bluetooth, DECT phones, video sending devices, microwave ovens, smart Phones, tablets, PC’s, barcode scanners and even Electric motors (the first RF transmitter invented).  So unlike other environments, we can conclude that healthcare environments are certainly ripe with interference.  I expect this to only get worse as we see more consumer class devices entering the space!

I do agree with the authors, there are no formal standard that defines a standard set of tests that addresses the coexistence problems – at least none that I’m aware of.  But what is to be gained from a standard set of testing procedures for medical device manufactures and healthcare organizations to follow if by definition of the ISM band devices must tolerate such coexistence challenges?  Well perhaps some – I know some medical devices do not employ antenna diversity, nor is polarization of the antenna a major design consideration – both called out in the article as tests that should be considered.  Receiver sensitivity also is somewhat – less than optimum than current chip sets can provide.

Coexistence testing may in fact improve wireless connectivity to a degree, but I strongly suspect it won’t move the needle much – not given the ever increasing number of ISM based devices entering the healthcare environment.  There are simply no guarantees of a clear channel in the RF world – licensed or unlicensed!  What we need to do as an industry is to create a standard that helps to evaluate the end-to-end connectivity aspects of wireless medical devices – but to some degree the IEC-80001-1 standard if applied would be a step in this direction, but not during the design phase of a medical device…

Medical devices today need to embrace the intelligence of 802.11 networks can bring.  Things like more intelligent roaming & authentication, QoS, adapting to dynamic channel changes to avoid sources of interference would be top of mind.  Why stay on a channel that has been compromised due to interference when there may be another better performing channel available in the service area.   Some Many of these devices are “sticky” in that they tend to stay associated to an AP down the hall even when there is one located directly overhead.  Roaming performance is also an issue to consider as many of the devices are mobile not only on a floor/building but between floors or buildings.

So I agree, coexistence testing may help move the needle, but embracing the intelligent network technologies available in today’s 802.11 network would be more fruitful.  The article is well written and very much worth the read (great job guys) – it does call to light some issues and I would like to see a standard developed to include end-to-end considerations for safe and effective wireless medical devices.  In the meantime however, IEC-80001-1 might prove to be useful in calling these issues to light during the post design phase of the products lifecycle.

What testing does your healthcare organization do for assuring wireless medical device connectivity, and if you’re a medical device vendor – what are your thoughts?

Your silence counts as an answer too 😉

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  1. We are wireless at our clinic. We started testing electronic medical record use with an Ipad. Once we got the ball rolling with one, we started adding users. So far, there hasn’t been an issue with interference, though maybe that’s just luck.