Update on welding with implanted defibrillator

You are throwing a big EMF and RF wrinkle into the system that they never thought of during initial testing and field trials, and doesn't come up all that often in use - They simply expect all of the grateful recipients of their medical largesse to meekly back down and give up all activities that would add the slightest bit of extra hazard, including an irrational severe allergy to microwave ovens.

They don't know you very well, do they? ;-P

Don't feel bad, that's the same faulty logic behind the "No 2-Way Radios or Cellphones in the Hospital" decrees. Rather than study the potential conflicts and determine limits that are technically required, a blanket edict is a whole lot easier and faster.

Dead guys can't weld anymore, yes. But guys who can't weld anymore might as well... No, let's not go there any sooner than we have to.

They have to look at this as a Quality Of Life issue, and your task is to beat that fact through their heads. With their own arm.

If nothing else, get some hard numbers on limits, and get them to sign off on your sensor suite to measure them real-time. You are developing a new study group, one researcher and one patient. No rules that they can't be the same body.

You might end up with a vest that has sensors and a big buzzer - when the sensors go over limit the buzzer goes off, it's time to reposition the weldor, the work and/or the cables.

And there is always that mule-kick internal alarm if the external one doesn't work - that should provide impetus to get it right the first time.

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I used to work RF/Radio. It never stopped their security people from using radios anywhere that I could tell.

I remember one emergency room radio/install that gave us fits. Sometimes when they keyed up the local base, (security office was right beside the ER entrance. Common configuration.) the main ER entry sliding power door would open/cycle. That one was lots of fun!

All sorts of radios wandering around ER back then. Police, security, ambulance, two-way techs...

I remember VP Cheney getting one of these or similar a while back. It seems like that should have opened a can of worms trying to keep people for making it go off falsely.

I'll bet he didn't volunteer to stand in front of the new crowd control gizmo that they were pushing/demonstrating.

Years ago when I was the lonely IT guy, a supervisor keyed his radio right next to my main server and it abended. I think he saw his demise in my eyes, he sure left my office quickly.

Wes

Sheesh, you have a nice junkbox. I tried newark and digikey and they didn't carry it.

Thanks,

Wes

A very good point, Pete. Our half-hour conversation with the device nurse persuaded me that these people really do "tune" these things to the individual patient.

Mercy Heart Center (Coon Rapids) was rated one of the top 100 Cardiovascular hospitals in the nation every year 2003 thru 2007. I don't think these people are hacks. I do think the young doc just hadn't dealt with a question like mine (or crusty old engineer like me) so he went into defensive "blow smoke" mode. There ain't a soul alive with Dr. in front of his or her name that didn't become proficient at that in grad school. It's a survival skill.

They probably don't research options beyond medical considerations. That's now OK with me. Having done some of that research now, I can see why. They don't have the training in physics or engineering, and it's impossible to rigorously research an undefined situation with several variables. I can research my particular situation, and I'm doing that, but I doubt that they'd know what to do with the data any more than I can read an XRay or interpret a lab report.

I learned that parameters "could be optimized for welding" from a senior (as in top-level) engineering fellow but he didn't say what compromises that might entail. I'd rather it be optimized for intended medical function, then I'll compromise as necessary re hobby welding. Initial field strength measurements made today with MIG (in my particular situation) are quite encouraging.

I doubt if he'd care, but the guys at Boston Scientific have expressed interest. I sent them an update report with photos tonight. If you'd like to see it, lemme know.

His view is that he will adjust the device to protect me as much as possible. Ya can't optimize everything. Optimization is almost always a "best compromise". In order to do it, one must prioritize the set of outcomes, taking into account their probabilities and cost or benefit.

I can easily understand how a concientious Dr. would balk at compromising medical optimality for a rather ill-defined need or desire. I can't fault him for that. How much does he tweak this parameter or that to achieve what gain in meeting the new goal? If I were he I'd take the same course he's taking.

Lifestyle adjustments do sometimes result in more quality life, which has some appeal for me. I don't want to live life past the point of enjoying it, but life is still quite enjoyable. I hadda quit smoking, I'm now walking 3 brisk miles every (goddamned) day, etc.

I'll be MIG and/or TIG welding after the procedure only if I'm reasonably confident that I won't get whacked on me arse by doing it. I'll still be gas welding and brazing in any case.

I got it from DigiKey some time ago. It's not a current part, I've had it awhile. Parts now available from Allegro, Melexis, Honeywell and others may well be better.

See

Allegro has been generous with samples in the past, don't know how they are these days.

If you could use a couple of single-ended (not differential output) ratiometric linear hall sensors, ping me by email. They're Honeywell devices from a decade ago. I have a spec sheet I can scan.

Amalog Devices also makes Hall Effect sensors. They should be avaialble from a number of distributors.

Doug White

You can also often obtain them from the brushless motors of old floppy drives, etc. They often use three hall effect sensors to determine the angle of the magnetic rotor, in order to commutate the current to the windings of the motor. You'd have to guess at the specifications, but if in doubt about how to use it, you could measure the voltages with a scope whilst it is still working in the floppy drive.

Chris

I found a single ended one in Newark. I'll play with that. I thank you for your kind offer.

Btw, I liked Joseph Gwinns idea of you turning your sensor into a warning system should you decide welding is managable.

Wes