Do-it-yourself EEG, EKG, and EMG

I have been under the impression that doing this kind of thing is not that difficult (as explained here) but somewhat "dangerous" in that if you get the wiring at all wrong and accidentally apply even a small amount of current you can confuse the heart and get it to damage itself. I do not see any paragraphs here of "dire warning" or even any specific mentions of parts of this process being dangerous, just a comment that "it seems to me almost impossible that anybody could injure themselves", which I'm finding strange ;P.

Here is a much older article from 2003; it begins with a dire warning.

http://www.eng.utah.edu/~jnguyen/ecg/ecg_index.html

> This device requires you to strap electrodes across your chest. This is inherently dangerous. Both because of the pain caused by sticky tape pulling hairs out of a person's body and also because even small currents can kill. Do not attempt this experiment unless you fully understand the potential problems with this device.

Here is another article from 2007; again, it begins with a dire warning.

http://web.archive.org/web/20070324054626/http://www.e-dsp.c...

> Before I continue to explain what I did, I would like to WARN you! 500mA (miliAmps) on 220V will completely destroy your nervous system (so run it from battery supply), check everything twice and you are responsible for it on you own.

In this article from 2013, there is a rather extensive back/forth paragraph ;P.

http://www.swharden.com/blog/2013-04-14-simple-diy-ecg-pulse...

> If you’re worried about electrical shock, or unsure of your ability to make a safe device, don’t attempt to build an ECG machine. For an ECG to work, you have to make good electrical contact with your skin near your heart, and some people feel this is potentially dangerous. Actually, some people like to argue about how dangerous it actually is, as seen on Hack-A-Day comments and my previous post comments. Some people have suggested the danger is negligible and pointed-out that it’s similar to inserting ear-bud headphones into your ears. Others have suggested that it’s dangerous and pointed-out that milliamps can kill a person. Others contest that pulses of current are far more dangerous than a continuous applied current. Realists speculate that virtually no current would be delivered by this circuit if it is wired properly. Rational, cautionary people worried about it reduce risk of accidental current by applying bidirectional diodes at the level of the chest leads, which short any current (above 0.7V) similar to that shown here. Electrically-savvy folks would design an optically decoupled solution. Intelligent folks who abstain from arguing on the internet would probably consult the datasheets regarding ECG input protection. In all cases, don’t attach electrical devices to your body unless you are confident in their safety. As a catch-all, I present the ECG circuit for educational purposes only, and state that it may not be safe and should not be replicated There, will that cover me in court in case someone tapes wires to their chest and plugs them in the wall socket?

Dr House should be both delighted and worried by this. We are seeing the flowering of an age where sophisticated medical diagnosis is just a (well regulated and tested) app / dongle away. From on chip chemical analysis to home brew EEG the things that say a child born today in Africa will see connected to them will astound you and I.

I hope it it makes the difference between the infrastructure it has taken to build to get care within our reach and the less infrastructure available / needed in different corners of the world.

If you're interested in playing with EEG, you might want to also check out the new Emotiv Insight headset:

http://www.kickstarter.com/projects/tanttle/emotiv-insight-o...

> [..] and the person hypothetically has a heart condition.

That alone is a massive problem - how do you know? Most people only discover things like this when things start going wrong. And if you make things go wrong, then you risk doing even more damage. I've never had any of the tests done professionally, but I imagine there is a certain amount of assessment that takes place before the tests are even conducted.

You are incorrect. This circuit can potentially apply unsafe currents across the patient. A standard medical biopotential measurement circuit will have single-point failure protection to prevent conditions like this. This is required by standards like EC11, EC13, and 60601. Those systems are extremely safe.

Most hobbyist designs, like the one in this article, do not have such protection. Indeed, for this particular circuit, a simple static discharge, as might happen when you're applying the electrodes after walking over carpet, can fry the input amplifier, connecting it to the power rails. ESD (and, indeed, defibrillation -- which is about a thousand times more energy than ESD) protection would be present and required in any medical biopotential amplifier, even unrelated to the single-point protection described above.

If the ESD failure happens to short out to power rails, your current will be your power rails divided by your electrode impedance. This distribution is described in EC11/EC13 (although electrode technology has improved since the days when those tests were done, so impedance is even lower). Even with the ancient electrodes in EC11/EC13, you would get unsafe currents some of the time. With modern electrodes, you would get unsafe currents much of the time.

I've seen dozens of circuits for home EEG/ECG/EMG. Almost all of them, including this one, are a deathtrap. They will work okay most of the time. At some point, someone's going to kill themselves.

Disclaimer: I am not a physician, but I've designed ECG circuits all the way through safe, successful human trials.