defibrillators

RichD wrote

Was it not a sort of taser? ;-)

No, but I've just (10 days ago) had a pacemaker implanted. And was accidentally told about more complex devices that also act as defibrillators. Glad I don't need one of those...

Mike.

It sends a hefty pulse of energy to the electrodes. For operational theatre use, up to 400 J (Ws). In the thing I was building, the pulse was 3 kV to a 50 ohm load. The electrodes have to be covered with contact paste and the high energy pulses still cause nasty burns, despite that the electrodes are up to 4 inches in diameter.

The small portable units are running at lower energy levels.

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-TV

AIUI, if the heart has lost its rhythm, the shock will stop it, in the hope is that it will restart properly.

IANAC

Cheers

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Clive

As for what's inside some old external ones:

He has some videos about implantable ones too.

I've gone into atrial fibrillation a few times - which is whole lot less of problem than ventricular fibrillation which kills you quite quickly.

The cure for atrial fibrillation is a big enough electric shock through the chest to stop the heart, and a second - smaller - shock a second or so later to start it up again, hopefully in normal - sinus - rythm.

If it doesn't work right the first time, they try again, almost instantly.

They do it under a quick-acting general anesthetic, so I can't say any more than I was told at the time.

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Bill Sloman, Sydney

I don't think the small portable ones for public use (AEDs) shock twice though.

A respected medic of my acquaintance said that in her opinion, if you're not too far away from an ambulance, best to keep up chest compressions and mouth-to-mouth till the professionals arrive. The AEDs require quite some time when you can do neither.

Cheers

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Clive

of problem than ventricular fibrillation which kills you quite quickly.

rillation

he chest to stop the heart, and a second - smaller - shock a second or so l ater to start it up again, hopefully in normal - sinus - rythm.

.

re than I was told at the time.

The paddles are sensors as well as shock delivery contacts. The defib sense s the various phases of several kinds of heart contraction waves and then d elivers the right energy pulse at precisely the right phase of the contract ion to coax the contractions to fall back into productive synchronization.

From what I can see CPR is an emergency treatment for cardiac arrest and not a defibrillation technique.

Assuming here you mean the smart AED defibrillators for the public to use rather than the proper medical ones where you can change the shock pulse energy, length and even see the actual EGC waveforms.

Basically it consists of an EGC with dual purpose sensor pads and if appropriate it administers an electric shock of the right sort to stop the heart and allow it to restart with a stable pumping rhythm again.

It is smart so it won't shock a healthy patient and it warns when it is about to adminster the shock. Some require you to press the button. It talks you through what to do and when and has a slightly annoying metronome for doing CPR by which for some reason persists even if the patients heart has recovered a good rhythm. If there is no heartbeat then it will offer to shock the patient every couple of minutes.

When/if the real paramedics arrive then they will use their own kit.

If the heart is no longer functioning as a pump you lose oxygen circulation to the brain and active cooling so damage occurs pretty rapidly if you don't do good CPR whilst the kit is being fetched and attached. Survival rate for the patient falls by about 10% for every minute that the heart is in a failed state so *time* really matters.

Ventricular fibrillation is the serious killer. It was someone suffering this sort of heart attack that led to our community buying one.

Have you forgotten how to use google? eg

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Regards, 
Martin Brown

Yes. The point is that CPR keeps some blood flowing through the brain but stopping to use an AED doesn't. The AED won't shock unless it detects fibrillation, during which time CPR has to stop. If an ambulance is only minutes away, there's a IMO valid argument that CPR should not stop. Tough call.

Cheers

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Clive

Yep, V-Fib is what happened to my wife 3.5 years ago. Firefighters took a long time to de-fibrilate and it finally worked... But too long without O2 and despite my doing CPR before that did not help.

Evidently scar tissue on the inside kept the conduction of the synchronization pulses to that part of the heart.

Used to work at a place that made defibrillators as well as cardiac stress test systems. 360 Joules max and 5 kV capacitor inside. I think I remember that the Defib pulse was synchronized to the R wave some how.

Used the defibrillator once to burn out a short in a prototype circuit. Worked great ! boB

Thanks John, I hope not to need to use that information.

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 Thanks, 
    - Win

A high voltage generator, capacitor, and some control stuff. Basically a big-ass flash unit with different controls.

It stops the heart - the idea being that the heart will restart, normally, on its own. It does nothing for a heart attack (MI), unless the heart goes into fibrillation, tachycardia, or some other arrhythmia (stop, restart). I does nothing for cardiac arrest, even. The heart already stopped and it didn't restart itself so whacking it again does nothing. It's only purpose is to correct an arrhythmia (which is big enough).

Just had them used on me (multiple times over past decade, or so).

At 100J, I can see burns, showing the outline of the pads (about 6x8", IME). At 300J, the outlines are filled in (6x8" burns, front and back).

I believe the AEDs hanging on the walls in public places can deliver at least 100J and paramedics can deliver full 300J zaps.

Correct. A defib will do absolutely nothing for someone in cardiac arrest. Chest compressions may save his life. An AED shouldn't even fire if used on someone in cardiac arrest. They need to sense the arrhythmia (and I believe they time the shot to the optimum point - Internal Cardioverter/Defibrillators do - ICDs).

I spent a few months (around 1998) working for the guy who had (in another job) developed the CMOS integrated circuit used in the first implantable defibrillator/pacemaker.

He was quite proud of the on-chip isolation scheme the let him get 36V of defibrillation voltage out of a low-voltage CMOS part, and very happy to talk about it.

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Bill Sloman, Sydney 
Bill Sloman, Sydney

Except reduce their chances of survival by wasting time as it checks for fibrillation.

Cheers

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Clive

Ours in the UK came with a free training course from the NHS paramedics who were involved in community outreach for the AED programme.

Are you sure about that? All the ones in the UK are supposed to go through a cycle of hit the heart with a shock and then monitor the heart. It is advised that you check for a pulse at this point since the thing isn't quite smart enough to let you know if it has found a heartbeat and continues to go through the CPR drill. After 2 minutes if it still can't see a heartbeat it will try to shock the patient again. The guy who did our training said the unit could source something like

600 shocks. They take the unit with the patient as it has recorded the EGC and the actions taken internally but return it fairly promptly.

The self adhesive gel electrodes once opened are scrapped in the first world but reused elsewhere.

Some of the older community AEDs are like that here and it prompts along the lines of "shock advised" when it has armed itself but someone has to actually press the button to adminster the shock.

CPR is mainly a way of keeping the patients brain oxygenated and cooled until the paramedics arrive with the right kit to restart the heart. It can cause pretty serious bruising or broken ribs.

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Regards, 
Martin Brown