How am i still alive ???

[Alarm]

QFA

BTW I presume you know that people who have been shocked are advised to go to A&E since some of them suffer a heart attach hours later.

Have you?

 

[bernardgreen]

BTW I presume you know that people who have been shocked are advised to go to A&E since some of them suffer a heart attach hours later.

Or have injuries to other internal organs such as burns or damage from muscle spasms that occured during the shock. These injuries often present no external indication.

Are you still there?

He could be if A&E are busy / understaffed.

 

[JohnW2]

This is getting rather seriously off-topic, but ....

Again quoting from Philips public domain documents. ....

Indeed. Modern machines are getting pretty clever. What that document demonstrates is the way in which a modern electronic defib adjusts to try to achieve the same current-time integral (which is essentially what matters in terms of defibrillation) in the face of varying impedances of the patient's body.

The Lown waveform is that which one would get from the discharge of a capacitor via an inductor into a complex impedance such as that which the human body is. The second half cycle is the energy shock stored in the body returning to the capacitor and was not "intentional" from the de-fib.

It may have started as 'unintentional', but it rapidly resulted in a realisation of the value of a relatively small 'reverse current' following the main shock increased efficacy and reduced the main shock current required (which, amongst other things, reduced 'collateral damage'!). Fairly crude capacitor/inductor defibs continued for a long time, and some may still be made today.

In the 1960's testing of de-fibs involved a dead pig's body as the best ( easiest with available technology ) simulation of the human body.

Indeed, although we mainly used live (anaesthetised) pigs - if they're already dead, it's a bit difficult to study what effect the electricity is having on heart function!

The second half cycle of the modern bi-phase is intentional and the current in the second half cycle is sourced and controlled by the di-fibs electronics.

Indeed. I think that current machines generally use something they call a 'BTE' waveform (biphasic truncated waveform), along the lines in the page you've just posted - essentially a somwhat differentiated asymettrical square wave of one-cycle duration - much closer, in fact to a 'positive DC pulse' followed by a smaller 'negative DC pulse' than the damped sine wave of the Lown waveform and, as a consequence, even more effective.

If I recall correctly the second half cycle is intended to rapidly restore the electro-chemical status in the body that the first half cycle would have disrupted. This restore would occur much slower by passive dis-charge of energy from the first half cycle stored in the flesh.

Sort-of, but it's not in relation to the body as a whole, merely the 'electro-chemical status' of the heart muscle cells - the potential across their cell mebranes and the associated ion movements (mainly sodium, potassium and calcium) across their membranes.

However, all that aside, it remains the case that a DC shock to the heart (whether monophasic or biphasic) can, if adequate, 'stop' the heart (produce 'asystole') and leave it in a state where it is quite likely to re-start spontaneously, whereas if an AC shock is large enough to have a major effect on the heart, it is far more likley to result in ventricular fibrillation, which very rarely terminates spontaneously (until death!) and therefore is usually fatal unless treated by defibrillation.

Kind Regards, John.

 

[JohnD]

QFA

QFA may stand for:

Qantas Airways
Qatar Football Association
Quantum finite automata
Qualified Financial Adviser (Republic of Ireland)


Which did you mean?

 

[Alarm]

Quoted For Agreement.

How long you been on forums

 

[JohnD]

Joined: 15 Nov 2005

 

[Alarm]

I meant how long,not just here. And it was not an insult.

 

[JohnW2]

Quoted For Agreement. How long you been on forums

I've been involved with forums since long before 'the Internet' (www) was born, but it's always meant 'Quoted for Accuracy' to me

Kind Regards, John.