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Author Topic: QRO and Pacemakers  (Read 4807 times)
K8AXW
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« on: August 09, 2012, 08:53:20 PM »

Greetings all:

Anyone with first hand experience with running QRO and a pacemaker onboard?

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K7KBN
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« Reply #1 on: August 09, 2012, 09:23:43 PM »

Not on HF...
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73
Pat K7KBN
CWO4 USNR Ret.
G3RZP
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« Reply #2 on: August 10, 2012, 01:48:47 AM »

The EMC standard (ISO 60601)  for implants now requires immunity to 10 volts/metre. As you go higher in frequency, the body losses increase and you can reckon on 20 to 30dB at 400 MHz -  and 100v/m is not a field to be in! A study by Georgia Institute of Technology back in 1986 (published in RF Design magazine) found that no pacemaker designed after 1982 fell over until the field strength exceeded safety limits, and that without body attenuation.  Implants fitted with radio transceivers meeting European requirements - yes, there are about 500,000 of them out there - have to have the radio working in a 3 v/m  80% amplitude modulated field 5% off tune. However the body loss mentioned above means that in practice, this is a negligible problem for the implant, although not for the programmer to which it talks.

So provided the FCC limits for field strength are met, there should not be a problem. There is anecdotal evidence about problems from thyristor controlled railway locomotives operating from a 16-2/3 Hz supply, mainly because of the magnetic fields. and certainly, precautions are very necessary around welding apparatus. This is because the intense magnetic field has a low frequency component not attenuated by the filters. Incidentally, the pacemakers have some very expensive miniature low pass filters on the leads. A problem with fitting radio is that the EMC integrity gets breached by virtue of bringing in the antenna lead, but this has been satisfactorily solved.

I claim some expertise here as the Chairman of the European Telecommunications Standards Institute committee ERM_TG30 on Wireless Medical Applications.

Incidentally, if you have a pacemaker fitted up with radio for home monitoring, I do not recommend the use of power line telecommunication (BPL) inside  the house. It is popular over here for short range intra house work, but the effects of intermodulation and harmonic production by such things as wall warts can prevent the pacemaker communicating. This problem has been recognised in an ITU Report.

Hope this helps....or contact me direct for further info.
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WX7G
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« Reply #3 on: August 10, 2012, 04:31:11 AM »

http://www.arrl.org/fcc-rf-exposure-regulations-the-station-evaluation

http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet65/oet65b.pdf

Here is a power density calculator. http://hintlink.com/power_density.htm

You will have to convert the power density to electric field using the 377 ohm impedance of free space (assuming the pacemaker is in the antenna far field). Where the calculator says Average power input the Peak power as the pacemaker will respond to the peak and not to the average value.

P = (E^2)/R

solving for E, E = (PR)^0.5, that is electric field equals the square root of the quantity POWER X 377 ohms

For evaluating my station I use EZNEC to obtain RF exposure levels.

    WX7G, Narte Certified EMC Engineer
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KC9PRE
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« Reply #4 on: August 10, 2012, 06:23:44 AM »

I think you will be fine. I have had several patients who have been treated in the chest area that have pacemakers  with 15 megavoltage x-rays. We used to monitor them but,not anymore since there was never a problem.
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WX7G
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« Reply #5 on: August 10, 2012, 07:12:40 AM »

I don't know what the correlation is between X-rays and HF RF and would not rely on that anecdotal evidence.

If you want good assurance (but not a guarantee) that there will not be a problem keep the E-field below 10 V/m (or whatever your pacemaker is specified for). Anything above this level and you are taking a risk. What the result of a malfunction is I don't know but you could keep increasing power until a malfunction occurs or you reach the limit of your amplifier. Make sure to modulate the signal, such as running CW with DITS. Let's us know how it went, if you are able to report back.
« Last Edit: August 10, 2012, 07:15:12 AM by WX7G » Logged
K8AXW
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« Reply #6 on: August 10, 2012, 08:18:27 AM »

Thanks all for the info.  RZP, I might be contacting you direct.  I have to wait to see this through..... I might luck out and not have to have one implanted.  I have a tendency to "jump on my horse and ride off in all directions at once" as Mark Twain said.

Quote
if you are able to report back.
  I liked that!   Grin
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WB6MMV
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« Reply #7 on: August 10, 2012, 08:30:06 AM »

Allen:

I designed external and implantable defibrillators and pacemakers for 15 years.  Your concern about QRO is not something to worry about.  We have design models that expose the designs to various situations to verify that the device won't react adversely.  They are far beyond what most people could be exposed to.  With respect to HF emissions, your risks are slight; we spent most of our time on Vhf and Uhf issues and things like welders, MRI machines, etc.

I would, however, suggest that you read what the manufacturer of your pacemaker says about external emissions and if you weren't given any direction by your physician, contact them for that data. That should give you some peace of mind. 

Ken WB6MMV
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G3RZP
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« Reply #8 on: August 10, 2012, 08:37:15 AM »

I believe all pacemakers these days revert to steady pacing at 60 beats per minute if they decide there's an EMC problem.

Biggest problem areas appear to  be the lead connections getting dodgy. Also, some patients, because they can feel it when it's not very deep, push the thing around under their skin. Some even manage to rotate it 180 degrees and strain the leads that way!

But also try talking to the manufacturer when you know what the model is. Most of them have a ham or two on the staff who understands these things! When they talked of me perhaps needing one, RF EMC was the least of my worries - they decided in the end that I could carry on just with medication. One problem that causes some complaints is that modern pacemakers have so many programming modes that many physicians can't actually understand and use all the possible facilities. Bit like me with a modern microprocessor controlled transceiver!

Depending on the model, if it has a built in transceiver, it might be a good idea to avoid having one of these palm sized 70 cms rigs in your shirt pocket while transmitting. Implants generally use the MICS/MEDS band at 401 to 406 MHz: maximum radiated power is 25 microwatts, and 1 mW tx into the average implant antenna can get nowhere near that.

OK, someone who works with powers that low shouldn't be on an Amplifiers forum......
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W4VR
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« Reply #9 on: August 10, 2012, 10:00:05 AM »

Should not be a problem, however if there is any doubt check with the manufacturer of the device.
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G3RZP
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« Reply #10 on: August 10, 2012, 11:00:38 AM »

If the manufacturer says there is a problem, ask for a copy of the official test report, and look very carefully at it. If they don't want to play, go for a different manufacturer - there are plenty of them.
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K8AXW
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« Reply #11 on: August 10, 2012, 06:07:26 PM »

One and all, many thanks for your input and encouragement.  My wife had a pacemaker implanted several years ago and I spent a great deal of time trying to get answers to the same question I posed here.

The manufacturers simply play the "dodge-ball" game with the questions and never answer them.  In other words, they just won't provide any answers!  Which is understandable considering the lawsuit situation in this country.

My wife's cardiologist, when asked the question, looked at me with glazed eyes with no idea what I was talking about and then reverted to the "cover my ass" answer of saying "stay away from high power RF."  I've tried to do that very thing and so far she hasn't had a problem.

This is why I posed the question as I did here.....asking for "first hand experience."

Again, many thanks!

Al
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WX7G
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« Reply #12 on: August 10, 2012, 06:55:27 PM »

So, to use QRO one would place the antenna far enough from the pacemaker individual such that the E-field would always be less then 10 V/m.

Or, as stated rely on the pacemaker defaulting to 60 BPM if subjected to too much RF.
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K6AER
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« Reply #13 on: August 10, 2012, 10:10:16 PM »

In 1977, fresh out of collage with my BSEE degree, I went to work for HP in Waltham, MA as a young RF engineer.  I worked with several senior RF engineers and we developed the first UHF halter monitor so patients could roam the hall ways after a heart attack and have their EKG  monitored. Pace makers were just being developed and many designs were competing for a lucrative business.

The question came up as to the sensitivity of pacemaker to RF and because we had a 250 mW UHF Transmitter wired to a persons chest we had to find out how sensitive they were. We found in an antenna chamber and  it took over 300 watts EIRP directed to the pace make to get it to skip a beat. This was at a distance of 10 feet. Now this was in the open and not in a human body. We could not find any volunteers for a transplant and subsequent testing although I am sure HP would have paid very well.

The human body is over 90% water with other elements.  So we put a pace maker into a plastic barrel of water weighing about 150 lbs. and went back to blasting the water drum with over 2000 watts of directed RF. This was the maximum level of a UHF amplifier we could rent. The water did not change temperature and the pace maker did not skip a beat. The antenna was 10 feet from the water barrel.

At HF, because the wavelength is much longer, there will be much less effect on the human body. Water is a pretty good RF shield.

I know this is a very popular topic but you have a much higher chance of getting hit by lightning than suffering the effects of RF.
« Last Edit: August 10, 2012, 10:12:54 PM by K6AER » Logged
G3RZP
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« Reply #14 on: August 11, 2012, 01:53:13 AM »

We have to be a bit more sophisticated than a barrel of water. It is water with various salts and sugar and so on in it: a gooey liquid that really makes a mess of an anechoic chamber when it leaks! ( Don't ask....) There are differences between the solution for 400 MHz and 2.4 GHz too.


To put things in perspective, an input paper by the BBC to CEPT Project Team SE21 in 1993 showed that the TV transmitters around London subjected 400,000 people to an average field strength of over 400mV/ metre for each channel. That's nearly 3V/m peak just from TV, let alone cellphones etc.
Admittedly, the FCC radiation limits are based on thermal effects, while the implant will respond to short pulses, but it is a good guide.

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