The Workings of a Defibrillator
March 6, 2005 – 9:49 pmA defibrillator is a medical device used to electrically stimulate a faltering heart. Defibrillators can be used externally or implanted. I have read a little bit about the two main purposes of a defibrillator: to speed up a lagging heart rate or to force a “restart” of a heart that has gone chaotically out of rythm. I first found out about these devices eight months or so ago (when my grandfather had one implanted), and I had some questions then that I have just recently started to go about answering.
I had a couple of hardware questions, but most of my curiosities were about the software. On the hardware side, I was curious if there was some sort of mechanical transducer that converted the mechanical input from the beating of the heart into an electrical signal or if the defibrillator went straight to the source and tried to measure the electrical signals sent to and from the heart itself. It looks like the latter is the case (which makes good sense). This article seems to be the best one I could find regarding technical information about defibrillators.
On the software side, I still have some questions, and it seems like this kind of information isn’t as openly available (at least in the few minutes of web searches I have done). I am curious what algorithm one would use to determine a heart rate is sufficiently slow or irregular. Is there some time averaging taking place during a known healthy period to generate a unique patient baseline? On what time (or frequency) scale does a deviation from this baseline fall into the realm of requiring correction? I’m assuming all of this analysis is taking place in the frequency domain, and I guess I’m just curious how run-of-the-mill some of these algorithms are. Maybe they’re terribly specified to this particular problem or maybe they’re as general as any signal analysis techniques used at the undergraduate level. Something about which I hope to learn more.
5 Responses to “The Workings of a Defibrillator”
I think your right about the analysis being done in the frequency domain. My best guess would be that the device samples the heart’s electrical signals, and performs an FFT. Certain frequencies are associated with trouble - perhaps higher frequencies with small amplitudes (in time).
A problem with this is that the bad event is a transient phenomenon, while the FFT assumes the process to be stationary. What could be done would be to use other transforms, such as the quadratic Wigner-Wille transform. I doubt they would do that though, probably relying on a windowed FFT.
By Kristján on Mar 7, 2005 at 7:10 pm
I also think you’re right about the analysis being done in the frequency domain.
By Kristjan on Mar 7, 2005 at 8:25 pm
If you really want to know about this stuff, remind me to put you in touch with my brother, who might be able to answer your questions. To put things simply, he’s working on a computer model of the heart.
By Adam on Mar 8, 2005 at 3:30 pm
That sounds awesome. I might have to take you up on that offer.
By jjk on Mar 8, 2005 at 11:09 pm
I am the “grandfather” who has the defibrillator implanted. Thank God for those of you who are so gifted to be able to figure how to preform such magic for those of us who need your help. All of you keep expanding your knowledge and you will be rewarded with great happiness.
By Al;ap340@aol.com on Mar 15, 2005 at 7:45 pm