defibrillator

[George L.]

Hello,

I was wondering about external defibrillators that are used in hospitals and some portable units. When you see them on TV or in movies they charge up for a long time, and make the person jump in order to start their heart.

What takes it so long to charge, huge capacitors?
Also, does it deliver high voltage, high current or both?

I am just curious.

thanks,

George L.

 

[spuffock]

Right first time, huge capacitors. Both high voltage, hundreds of volts, and high current, up to ten amps or so. I believe units are designed to work best into 50 ohms.
By the way, the unit stops the heart, when it starts to writhe instead of beat, in the hope that it will restart itself in the proper rythm.

 

[Nigel Goodwin]

Right first time, huge capacitors. Both high voltage, hundreds of volts, and high current, up to ten amps or so. I believe units are designed to work best into 50 ohms.
By the way, the unit stops the heart, when it starts to writhe instead of beat, in the hope that it will restart itself in the proper rythm.

Yes, almost all the uses of them on TV are complete rubbish, it actually STOPS the heart - useful if the heart is fibrillating - beating under it's own control, and not the brains.

The portable ones are really cool! - completely automatic (even to talking you through placing the electrodes), they even check the heart to decide if it needs shocking or not, and calculates the advisable level. They are pretty well indistructable as well (or at least VERY strong), the instructor on the course I did threw it across the room - and they cost thousands of pounds!.

 

[Styx]

Well I am a trained first aider (requiring refreshers every 4year). But abt a year ago we started to get in portable defibs and us first aiders were trained up with them.

Funny story it was actually Las Vagas that spear-headed the portable defib developement. Quite alot of their punters would have heart attacks (due to shock of winning or more usually shock of losing). When the paramedics would arive it would take them quite a while to get through all the crowds (biig places) and then they would have to bring them back to the ambulance.

Vagas casino's wanted to save the punters (cant bleed them dry of more money if they are dead) so they funded alot of R&D. The outcome portable defibs, however there still was the time getting the ambulance here and getting the crew (with portable defib) to the patience, hence pretty much all pillars have a defib on them and all security is trained.

IF advanced life support is intiated within 2min of a heart attack (oxygen, CPR & defib) then there is an 80% chance of survival compared to 2% if just waiting for ambulance (with an eta of 8min)


Anyway yup they charge up a effing high-voltage cap (not that high in capacitance) and then they "dump" it across the terminals. quotes at the refresh-courses are that there is enough power to light wembly stadium from one of the portables (I have to keep correcting them with "there is enough energy to light for an extreamly short period" but thats neither here nor there)

There are only two rythms that are shockable: ventricular fibulation or ventricular tachycardia and these unit's look for it, it wont allow you to shock if it doesn't see one of these (and will only advise to shock)


They are extreamly clever pieces of kit

 

[Nigel Goodwin]

They are extreamly clever pieces of kit

Yes, when I did the First Aid course they wouldn't let me take it to pieces!