Update on welding with implanted defibrillator

Don Foreman wrote: The

What I would worry about is the fast rise time stuff from the arc getting into the defib sense wires and having the induced noise interpreted by the processor as the erratic spikes of a heart in trouble. A 60 Hz sine wave is probably tolerable.

I used to use a lot of this stuff when I was chasing EMI fields:

If you want to try it in your test setup, send your address and I will send out a couple of feet.

Kevin Gallimore

Don -

Need to line a full leather welding coat with some netic-conetic metal. It won't magnetize and is anti. Used to shield O-Scope tubes from magnetic fields. Netic CoNetic sold by Perfection Mica Company of Chicago, Illinois. ..

Mart> >

This is a really good way to piss the good ones off. There must be a better way.

Joe Gwinn

I think you misspelled "a copy of the whole damned thread" ...

Myself, I wouldn't be all that worried about the mule-kick, you just tell the Doc that if it mis-fires you'll "pass it on" the next time you see him. Just like you felt it.

Then you mention that you work out with the Heavy Bag and light gloves so you're in shape to properly relay the message...

Then again, if your Local Doc is at all familiar with the field, dropping a big list of names of all the A-List people you have been calling and corresponding with to work out this problem just /might/ get his attention. You have to convince him to be as serious as you are, or yeah, it is time to get another Doc.

-->--

I don't think this guy is getting rich, working for Allina. He is probably a very competent physician and surgeon.

My mother was a physician, quit practicing back in the '70's because her employer (a University) worried more about legal issues than about doing what would be best for the patient. That situation has gotten significantly worse since then. These people are gunshy for good reason.

We talked to a "device nurse" today she of a couple decades' experience. That was interesting. I have known quite a few PhD's in engineering who were anywhere from incompetent to dangerous in a lab. Some technicans make contributions far beyond the recognition and pay they get. I'm an engineer with nevermind degrees, but I'm also a half-decent tech and I've always had enormous respect for good technicians. Nurses have more education than technicians though less than MD's. Nurses are traditionally strongly subservient to "doctor", it's part of the training and a requirement of the job.

We learned a lot from this nurse today. I will now be getting a Boston Scientific ICD rather than Medtronic, my preference based on the incredibly good support I've had from the folks at BSci.

I think we're making some progress here.

Magnetic field sensor done today, on the bench, electronics for it half done that I'll finish tomorrow. I now have some real specs, I have Fitch's datalogging scope-meter, we'll see if I can skin this kitty or whut.

Thanks, Kevin!

The leads they now implant are shielded and differential/bipolar, and I strongly doubt that they are inclined to experiment on live patients.

The devices employ both low-level analog filtering and digital signal processing. A V-tach heartrate of 300 bpm is still only 5 Hz.

Yeah it gets REALLY hard to find patients willing to have a unit trigger when it shouldn't. I can't imagine why? :-)

300 would NOT be a good thing!

Keep us posted Don. Who knows, some day years later, your words may speak to someone facing the same thing. After all Tee Nut lives on.

How does your sensor work? The only hal effect stuff I'm familar with is solid state sensor looking for a magnetic piston in pneumatic cylinder.

Wes

On Wed, 14 Jan 2009 23:47:32 -0500, the infamous Joseph Gwinn scrawled the following:

Yeah, I suppose you're right, Joe. But that money talk could be done more tactfully. He could suggest that he wants his doctor to know all there is to know about ICDs before he puts one into his chest, then start talking parameter adjustments.

-- A great preservative against angry and mutinous thoughts, and all impatience and quarreling, is to have some great business and interest in your mind, which, like a sponge shall suck up your attention and keep you from brooding over what displeases you. -- Joseph Rickaby

On Thu, 15 Jan 2009 00:46:35 -0600, the infamous Don Foreman scrawled the following:

Perhaps, but you want a surgeon whos is entirely knowledgeable about the device going into your chest, right? Were it mine, I'd insist upon it. When I hurt my back, I got 3 opinions. The first doctor wanted to operate on the wrong side (pain on right, he wanted to do a foraminal laminectomy on the left side of T4.) He's the one who had me in his office for x-rays, full physical, and consultation (the total time for those 3 services was just over 3o minutes) and then billed the insurance company $914 for the thick packet of crap he sent them. When I heard his recommendation, I asked him if he'd accidentally flipped the xray. I warned the ins co about him before declining.

The second was the foremost neurosurgeon in San Diego County at the time, Dr. Obenchain. He wanted to go in with an RF probe and burn out the nerves causing the pain. The procedure was fairly new with good results, but he hadn't performed it yet, so I would have been his guinea pig. We discussed the nerves in question and how they function to keep people from overtwisting the vertebra. Without those to give us pain, we could overexert and break our spines. I declined the offer as soon as he gave me the odds: 50/50. He said I will either get better or be worse off, but I wouldn't stay the same. That settled it.

The third doctor wanted to fuse T3, T4, and T5 together. FTN! (FTN = Eff That Noise!)

I opted for the non-surgical route. After a year off, I forced the insurance company to retrain me. Their idea of retraining was a $69 course for doing smog certifications. They wanted to put a man with upper back problems in a job hunching over auto engines and bending over to put probes in tailpipes all day. Again, FTN! I got a work comp attorney and he got them to settle out of court in the hour before it began. He couldn't believe our luck. She agreed to giving me more than the judge could have forced the ins co to award (about $11k

• training in Coleman College's Computer Electronics Technology course.)

Time and Nature have brought my back and body to about 85% of where I used to be with only about 10% of the pain I once endured, and some of that is kept at bay with chiropractic visits. I call that a win.

Yeah, juries award ungodly sums for minor mistakes.

Excellent! I've known a few nurses whose utterances I hold in much higher regard than I do any measly doctor's. They're in the trenches and get the real educations, and it's they who keep doctors in line and out of trouble most of the time, IMHO.

Indeed. I'm happy for you in that regard, Don. Keep on Trudgin! (...the happy road of destiny.)

GIFs at 11, please?

-- A great preservative against angry and mutinous thoughts, and all impatience and quarreling, is to have some great business and interest in your mind, which, like a sponge shall suck up your attention and keep you from brooding over what displeases you. -- Joseph Rickaby

On Thu, 15 Jan 2009 03:10:00 -0500, the infamous Wes scrawled the following:

Indeed. This thread will be live on Google for anyone doing searches on defibs forever.

and on, like frackin' Elvis and the Eveready Bunny.

--- I'm sorry Dave. I can't do that.

-- A great preservative against angry and mutinous thoughts, and all impatience and quarreling, is to have some great business and interest in your mind, which, like a sponge shall suck up your attention and keep you from brooding over what displeases you. -- Joseph Rickaby

My sis wore one of these for years, and had it trigger at some inopportune moments. One time while flyfishing in waist deep water. She still talks about that one.

Steve

A Hall effect chip is a bit of silicon that produces a voltage proportional to the strength of the magnetic field passing thru it. Imagine a rectangle with contacts on all four sides. Apply bias voltage from top to bottom. Electrons then flow from top to bottom -- but if there is a magnetic field normal to (thru) the rectangle they'll tend to drift sideways. This will produce a potential difference from left to right.

Modern sensors integrate a bunch of electronic trickery to improve temperature stability and reduce offset and drift, but that's the basic idea.

Many industrial sensors integrate this function with a circuit that switches at some level of field intensity, providing a binary or "on-off" signal. I'm using a linear hall sensor that provides a voltage proportional to field strength, about 4.25 millivolts per gauss. It's the HAL400C from Micronas. Current product would be the HAL401:

Why that one? Because I had 4 of them in my junkbox. Allegro also makes Hall sensors, and Honeywell used to, probably still does. I like the differential output on the Micronas for rejection of noise. 4 millivolts isn't much signal when 60 Hz is in the passband. You probably know what happens when the ground comes loose on a microphone or magnetic phono jack: HUMMMM! I want this sensor to sense magnetic field but ignore E field. I'll measure that separately.

It's differential output will drive an instrumentation opamp (Burr-Brown/TI INA121) with gain of 100, then a 2-pole lowpass filter with corner frequency of 200 Hz. I should have that all going today.

I think Richard Kinch plays fiddle and I play viola. Who in the r.c.m group is the cellist and who plays bass? We'll put the quartet together for you. And if the cellist is here, one of the guys over on the bowed strings group wanted to know the diameter of Helicore strings for a cello. If you've got Helicores on, get your mic out.

RWL

Had another thought today:

Perhaps the young doc hasn't yet encountered a patient who has expertise in a related field and doesn't yet know how to deal with that. It's not uncommon among highly-educated young chargers. I have ample experience with smoke, feathers, fancy dancing and bafflebullshit. I didn't deal with medical folks during my working life but I dealt with plenty of high-talent young PhD's in science and engineering.

A conversation with a decades-experienced "device nurse" was enlightening.

She said that the doc would not adjust parameters in an attempt to optimize compatibility with welding, he would adjust them to optimize performance for the medical purpose required and intended.

Well, duh! That's exactly what he should do. Welding is optional, dead guys don't need to weld. I could fault the young Doc's people skills but I gotta respect a no-compromise attitude re doing what is medically best whether I like it or not. That places responsibility for risk of welding squarely upon me, which is exactly where it belongs.

Everywhere I've worked, if you die, they send you home. Hope your bet works out in your favor.

Steve

The responsibility for the potential risk of welding belongs on you, however the responsibility to adjust the device to settings to accommodate the *requirements* of the *customer* belong on the service provider i.e. the doctor.

Do not loose sight of the fact that this is nothing more than a business transaction, do not get sidetracked by BS about the service provider wanting to do what he thinks is in your best interest. *You* specify the requirements, not the service provider and you should put those requirements in written form and make the service provider sign off on them.

The service providers role is to make recommendations and answer questions, your role as the customer is to ask questions and make decisions, even if your decisions do not follow the service providers recommendations.

On Fri, 16 Jan 2009 00:34:13 -0600, the infamous Don Foreman scrawled the following:

Excellent insight, Don. Gonna show him your DonRube device? ;)

I won't ask about some of that, especially the feathers.

But he should, as you'll be welding after the operation. He needs to adjust the device to protect you as much as possible, and that means to -your- lifestyle, not his optimum view.

Ah, more ammo for the operee. Carry on...

-- If we all did the things we are capable of doing, we would literally astound ourselves. -- Thomas A. Edison

The central issue is which requirements should govern if there is a tradeoff. The doc wants to optimize for best chance of intended medical function and performance with no compromise of that objective. I agree with that priority. I don't have to weld to survive, but I do have to survive to weld.