Build Your Own ECG

Jason writes "I finally finished documenting my $4 home made electrocardiograph (heart monitor). If anyone is interested or wants to build one for themselves, please come by and take a look. Makes me wonder why medical care costs so much. :)"

Comments

Please Come By...

[robbyjo]

...please come by and take a look.

Translation:

Please slashdot me and don't even peek... :-)

Re:Please Come By...

[Saint Aardvark]

Managed to snag a mirror while it was previewed to subscribers -- then had to go get beer. Mmm, Rogue Irish Stout. Anyway:

http://saintaardvarkthecarpeted.com

Gnome Toolbar Applet

[jkauzlar]

This could make a great gnome toolbar applet. Then I could enjoy watching my heart race when I accidently type 'rm -rf *' in the wrong directory!

Call me back

[m_chan]

when you can tell me how to build one of 'dem four dollar defibrillators. With my steady diet of coffee, butter and bacon, heck, that thing would pay for itself.

Oh, the irony!

[The-Bus]

And to think that today I used $4 to buy two Nacho Cheese Steak Chalupas at Taco Bell. While you were out trying to save your heart, I was slowly beating it into submission with slightly substandard but confusingly delicious Fast Food(TM).

Ahhh!

[shivianzealot]

I finally finished documenting my $4 home made electrocardiograph (heart monitor).

From the website:

Here you will find information how how to build one with less than $10 in parts.

Lies damned lies!

Re:Ahhh!

[IvyMike]

I'm pretty sure that $4 is in fact less than $10.

Re:Ahhh!

[VFVTHUNTER]

Whether it be $4 or $10, it's a helluva lot cheaper than the roughly $38,000 that people around the country are paying for Lifepak 12 monitors. And I would know, being a paramedic. I actually had to do quite a bit of ECG processing during my stint at the local college to get a bachelors degree...I can't decide which is worse for ECG processing, Matlab (which I used) or Visual Basic. Matlab is nice, but at $3000 a pop, Visual Basic is the cheaper way to go. Matlab's built-in functions definitely helped tho (***cringe*** at the thought of implementing the FFT in VB).

Perhaps the biggest problem with ECG systems is noise filtering. Adaptive filtering has failed miserably; you'd think the engineers designing the systems would implement Bass and Treble-style filters for healthcare providers to use, but condescention has gotten the better of them. Noise makes interpreting an ECG sometimes impossible, yet no such filters. This presents a problem for me on a weekly basis - it is sometimes impossible to interpret the rhythm, because the filters aren't working properly. If they'd only let me adjust the lowpass and highpass cutoff's, I would feel SOOOO much better. And if they'd give me a Savitsky-Golay filter, I'd have a wet-dream....here's hoping.

Slashdotted Already?

[Mr. Fusion]

His vital are dropping, maybe he should have looked into monitoring his school's server.

- clear -

Beep beep...beep beep...beep beep

-Mr. Fusion

My wife the nurse said ...

[TheGrayArea]

Yea, but does it interpret the data. That's one of the big expenses according to her: have the cardiologist examine the data and give his opinion. Since it's all waveform stuff, I wonder how much of that could be automated in the future?

Re:My wife the nurse said ...

[mgv]

Yea, but does it interpret the data. That's one of the big expenses according to her: have the cardiologist examine the data and give his opinion. Since it's all waveform stuff, I wonder how much of that could be automated in the future?

Its possible to automate alot of this stuff. However, its not as simple as it first sounds. I have used alot of ECG's with automatic interpretation, and they mostly get it right nowadays. About 95% of the time. Which isn't really good enough yet to risk your life on.

I think that you will find that eradicating the last few percent of errors will get harder and harder, and who is going to back (and assume liability for) any errors if not trained people - be they medical staff or highly skilled nurses?

I think that by the time that we can have automated diagnosticians, there will be alot of other things in our lives that are far less comples going automatic. Like cars that drive themselves and software computer programmers. But wait, I hear you say, nobody is anywhere near replacing programmers with software - but you think you are going to replace cardiologists?)

Just my 2c worth.

Michael

Re:My wife the nurse said ...

[Davak]

First thing we were taught in medical school regarding ECG is to ignore the computer interpretation. The sensitivity is way too high; therefore, the specificity is greatly reduced. Thus, the interpretation is seldom useful.

Where computer-automated reading of ECG is much more effective is in the automated defib units that you might find in airplanes, malls, ambulances, etc. The computer is good enough to know if a jolt of electricity would be helpful in correcting the problem.

Of course, the expense and the value of ECG is in the physician interpretation. Likewise, an aspirin in the hospital will cost you dollars instead of cents due to administration costs, nursing costs, insurance, etc.

What has really helped ECGs is fax machines and now the internet. If a health care professional has a question regarding a waveform, they can get it to someone who can give an accurate reading. Soon, if not already, physicians will be able to see the ECG live (and in living color) of patients on planes...

And quit dogging the editors for posting this... We need more tech-related medicine news. It warms this geek MD's heart.

Davak

Re:My wife the nurse said ...

[Frank T. Lofaro Jr.]

But wait, I hear you say, nobody is anywhere near replacing programmers with software - but you think you are going to replace cardiologists?)

Yeah, first we'd have to program a computer to be arrogant and have a God complex...

A warning to experimenters

[InterruptDescriptorT]

PLEASE be careful with ECG or EEG circuits, especially if you're planning to use an oscilliscope to see the wave or a data acquisition board to log the data. The pads and the gel used to adhere them to the skin and lower the resistance to get a good signal can sometimes cause current to flow into the body, especially if the circuit is not optoisolated.

Normally, the skin resistance is high enough to make the current flow negligible; however, when the pads are on, the resistance in the path is very low, and you could seriously injure or kill yourself if even a small amount of circuit flows 'back' through the electrodes.

Professional ECG machines usually have a lot of protection circuitry on their front ends (the instrumentation amplifiers) as well as between the amplifier and the ADC/output circuits to prevent this from happening. This is obviously even more critical in line- (i.e. 110V or 220V-) operated devices.

Re:A warning to experimenters

[pz]

PLEASE mod the parent up.

One of the reasons EKG systems (and I've used a fair handful) are expensive is that they go to extreme measures to insure that under no conditions will excessive current flow through the electrodes. (Ever wonder why hospital-grade power plugs are rated explosion-proof?)

I cannot comment on the original posting's circuit because it is slashdotted but I'm racking my brains trying to figure out how less than $10 can create a safe circuit ... and it might be possible, maybe, but probably not. Consider that another posting today described an electrified jacket which delivered debilitating shocks using a 9V battery as a power source!

Also, keep in mind that just because a circuit is battery powered does not make it safe once you attach the output to an instrument (computer, oscilloscope, DAC, etc.) which is plugged in to the wall.

Re:A warning to experimenters

[mgh02114]

We cannot emphasize this enough. By applying electrodes or gel to yourself, you are opening yourself up to "microshock" Current at the correct frequency can STOP YOUR HEART (technical term = ventricular fibrillation) This can happen at shocks as low as 300 mA if applied at exactly the wrong time and place. The risk depends on the frequency of the AC current. And guess what the worst frequency is? 60 Hz ... exactly what is coursing through your household current and appliances ... including the computer that you're looking at right now. Building an EKG was a simple homework problem in my Biomed Engineering course. My final exam was an EEG (brain electrical activity, not heart electrical activity). We paid a lot of attention to ground isolation and electrical safety. The key was to use a battery and not be hooked up to AC wall current at all. Unfortunately, the strength of an EEG signal is much less than EKG, and my final exam instrument wasn't working well enough to pick the signal out of the background noise. I got it to work by rubbing the skin off my temples so that the gell pads were on raw flesh (cutting down the resistance). Now that is what I call a "bloody hard" final exam.

Re:A warning to experimenters

[sigwinch]

One of the reasons EKG systems (and I've used a fair handful) are expensive is that they go to extreme measures to insure that under no conditions will excessive current flow through the electrodes.

Indeed. I took apart a pulse oximeter that used two levels of transformer isolation, and it didn't even make a direct electrical connection to the patient. (They use optical sensors that clip onto your finger.)

I cannot comment on the original posting's circuit because it is slashdotted but I'm racking my brains trying to figure out how less than $10 can create a safe circuit ... and it might be possible, maybe, but probably not.

It wasn't safe. Not no way, not no how. But I think you could do a pretty safe one for not a lot of money.

Use Ethernet transformers for isolation. They're rated for a coupla kV. The FDA probably wouldn't certify them, but I wouldn't be very afraid of them.

For power, use a 555 timer to drive one of the transformers. On the other side, rectify the current with a diode, filter it with a big cap.

To get the signal across the gap, use another 555 to turn the EKG voltage into frequency, and send the frequency across using the transformer. Feed it into the line input of the computer, do FM demodulation in software. Alternatively you can use a frequency-to-voltage converter (74HC-whatever PLL). Sound cards are terrible near DC, though, so doing the FM thing would give you the best signal.

Total cost would easily be less than $10. Even with medical-grade everything, you could probably make a production version for under $30 (in large quantities).

Medical equipment.

[Night0wl]

Oh don't get me started on medical equipment, [read: I'm going to get started on medical equipment]

Being disabled (SMA type 2, A type of MD, Donate to MDA!) I deal with medical equipment a lot, less then some in more critical situations, but more then your average user.
It's outrageous the markup medical tag gives to an item, one of the most outlandish of them that I saw was a flag, a metal mounting bracket, fyberglass rod, and cheap neon flag. You know the kind, sold in the walmart bike department for a measly 3$

Do you know how much they wanted at a medical store? No you dont.... 18$
So the price of "medical" is 15$ on top of 3$ It's insane.

You can buy an Ok car for the price of an electric wheelchair. And that's just for what's on the low end.

How exactly are people who can't walk suppossed to affoard this shit? Sure it's possible, and often times picked up by the government (thank god)
And if you're not covered, forget footing this bill your self, unless you've got cash to burn. And it's not like the freedom of mobility is important or any thing. Just one of life's liberties some people take for granted.

"I wish I could sit all day"

Fuck you buddy

Grrr, can you tell I'm bitter?

And then theres red tape. I've been using this same wheelchair for several years now, it needs replaced. But fighting for them is a nightmare. So much paper work.

Gotta be certified

[jpmkm]

Makes me wonder why medical care costs so much.

Damn near everything used in a hospital has to be certified to be used for medical purposes. People's lives are at stake, and you have to be sure that your device operates within tolerances, doesn't crash, doesn't electrocute people, etc. It costs money to think of every possible problem and design a device around that. Also, as other people have said, the people that run these things are some of the most educated people in the world. Try to start a hospital with your $4 device and let me know how it goes.

DANGER Will Robinson

[amasci]

It's not impossible to kill yourself with a badly-designed ECG device.

Places like UL/CSA say that voltages under 40V or so are safe. But if you apply it to electrodes pasted to your chest, the unsafe voltage is WAY lower than 40V.

If you build a simple ECG and connect it to a computer, that computer had better be battery-powered. If not, then you might get a nasty surprise (waking up in the afterlife of your choice.)

...you get what you pay for

[rfischer]

Congrats on what you've done so far...if you want to take the next step:

Higher-quality ECGs systems don't use generic op-amps, they use special devices called instrumentation amplifiers that are able to reject common-mode signals at the inputs really well. Turns out then when you place electrodes on the skin, the skin between the electrodes acts like a crude battery (we're full of electrolyte after all!) and you get a large, shifting potential difference between the two electrodes that can drown out the millivolt-range ECG signal.

Oh and by the way, the electrodes and wires will make great radio antennas (esp for 60 hz noise)! Check out the AD624AD instrumentation amp from Analog Devices.

Malpractice

[b30w0lf]

A disgustingly large amount of our medical expenses goes to malpractice insurance, and mostly to protect from one of the millions of malpractice cases that never should have been that occur each year. Granted, the ability to sue for malpratice *is* a good thing. However, it is grossly misused, and results in higher medical bills for all.

Not to say that's the only factor... but that's one of them.

It's dead Jim

[FIRESTORM_v1]

---^v---^v---^v-------

Eeep...eep...eep..eeeeeeeeeeee

time of death 927PM CST.
Damnit jim I'm a doctor not a webserver admin..

EXACTLY! MOD UP PARENT, PLEASE!

[wowbagger]

EXACTLY! Just what I was thinking when I saw this.

Kids, DO NOT TRY THIS AT HOME.

Real medical gear has full galvanic isolation - that means there is NO current path that goes from the patient's body to the equipment - the signals pass through either an isolation transformer, an optocoupler, or a capacitive coupling. That way, any ground leakage in the equipment won't fry the user.

It takes about .1 amp to kill you dead, and about .01 amp can interfere with normal heart operation. Normally, skin runs about 10 to 100 kohms resistance - to get 10 milliamps you would need about 100 to 1000 volts delivered across the chest.

When you put the gel on, you reduce the resistance to a few hundred ohms. Now you need only a volt.

Normal consumer equipment can have "leakage currents" - places current shouldn't be flowing but is. You hook your home-brew circuit up to the printer port on your PC, and maybe you are OK. Then one day, while screwing around with it, a cap starts to fizzle in your power supply, or maybe you reach up to adjust your monitor, or maybe you put your foot on the ventilation register. Then you get to start (posthumously) on the 6 o'clock news.

At a MINIMUM, you should power the circuit with a nine volt battery, and communicate with the PC via an opto-isolated RS-232 link.

Even better, splurge and get the real medical isolation amplifier modules. Yes, they will cost a bit more than US$4, but then, if that is all the value you place on your life....

On second thought - go for it! And make sure you clip the ground lead off your computer's power cord while you are at it. And do it in the bathtub - that will help shield the fnord rays out.

Why It Costs So Much

[istartedi]

There are several reasons healthcare is so expensive.

1. Litigation. Does the phrase "malpractice insurance crisis" ring a bell?

2. A side effect of (1.) is something called "CYA medicine". Ever receive a chest CT because your heartburn just might be a pulmonary embolism? It happened to me just recently.

3. Failed accountability. This one takes a bit more explaining. Ever bother to look at your bill? Of course not. Why? Because chances are, the insurance company pays it. Aha! You say. What if I'm not insured? Well then, many people who aren't insured "spend down" and go on Medicaid. Once more, nobody looks at what Medicaid is being billed, except for the hardworking beurocrats (cough)bull***(cough). Only the very narrow slice of the population that is "self paying" actually looks at a bill (more on thatlater) You would think that insurance companies would be on guard for their bottom line, but corporate inefficiency is often no better than government inefficiency.

4. Complex and inefficient billing. Health care is one of the few businesses where you receive service at a single location, yet billing goes from subconractors directly to insurance companies or patients. Worse yet, billing from some contractors takes weeks, or even months. Yuck! Imagine if every business worked like this. Imagine getting your car fixed, and you get bills from the mechanic, the parts department, and the oil supplier spread out over 2 months. It's not just inconvenient. It actually hinders your ability to make financial plans because you don't know what's coming. And why don't you know what's coming? That leads us to...

5. ...Secrecy. That's right. Secrecy. Try to call up a hospital and ask them for their price list. Chances are, you'll get the same answer I got: "That's on a computer and it's confidential". I was transferred to a manager who had her phone on voicemail. In retrospect, I should have known I was in trouble when the phone tree had "press 2 if you're an attorney". This is probably one of the biggest reasons healthcare costs too much. Sure, there are several hospitals within driving distance, but if I think I am going to need an exam that is likely to involve half an hour with a doctor, some medication, and an x-ray... I have no idea who charges the least for an x-ray, or what the hourly billing rate is for a doctor, or what the average examining time is for diagnosing a condtion. We have more accountability at the garage than we do at the hospital (Chilton's guides, posted labor rates, etc).This alone is probably the single biggest factor driving up healthcare costs. Lack of pricing information makes comparison impossible, resulting in a virtual monopoly even though there are multiple companies. So, what did I do? I gave up and paid a price that I could not verify as accurate because I knew that the only way to get the price list was to make a federal case out of it, and spend 100 times more in legal fees than my bill was.

6. Vested interests. You can call me a conspiracy theorist if you like, but I think various interests want the price of healthcare to skyrocket so that they can use that as an excuse to socialize it. The corporations actually secretly like the idea of socialized medecine, because then they get to become government agencies. If you are a corporate sleazeball, the next step up is to become a government sleazeball; the perks are just that much better. You can just hear them salivating.

Want to fix healthcare? Fine. Require providers to give one bill in a timely manner--no pass-throughs to subcontractors. Require providers to post price-lists online if they have a website, or to make price-lists available to the local libraries. Require employers who insure their employees to provider high deductable insurance. There should be no claims or forms until annual out-of-pocket costs exceed 10% of your annual pay. Place a cap punitive damages, as many have suggested.

um, $$$ because it can kill you

[SuperBanana]

Makes me wonder why medical care costs so much

Well, issues of "medical care" and "medical equipment" costs being two rather separate things(one of the biggest costs in medical care is liability insurance, probably followed by administrative overhead)...

...it might be because the expensive REAL version won't kill you when there's a lightning strike nearby, or when someone touches the case after building up a static charge, or something shorts out in the computer half...the list goes on. It only takes a few microamps to stop your heart- it's all in the path the current takes. Having those nice electrodes in the right places, making great electrical conduct with your skin...well, umm...you should get the picture.

Medical equipment is designed to be 'bulletproof' in almost every way- there's a standard, for example, for medical-rated Edison plugs and sockets.(Edison plug = US electrical plug). It's VERY heavy duty, makes really good contact, has excellent stress relief on the cord, etc...because something VERY important might be using it, like an artificial heart pump in an operating room, or a dosage machine for an IV, or a ventilator. The REAL version also can't crash or stop working- so, for example, if it has a computer, the instruction code, the chips...everything is heavily tested. Jokes aside, the Pentium math dividing bug is a perfect example of why you can't just use "anything" for medical equipment. What if that bug caused the heart monitor to display the wrong heart beat rate? Electronics used for medical equipment get a LOT more testing- lives are at stake. Same idea behind the MIL specs, although with MILSPEC stuff, the idea is more that the military really abuses the crap out of stuff ON TOP of similar concerns as medical stuff.

All of the above are why you often see these days disclaimers from chip makers that say "this device is not certified for use in life support equipment" and such. The statement often extends to industrial automation- "situations where malfunction may result in injury or death", stuff like that. Ie, "don't use this where if it screws up, it dumps 10 tons of molten steel on a bunch of steel workers' heads."

Your wife is correct

[The Tyro]

I can tell you that many of us clinicians laugh out loud at some of the machine "interpretations" that ECG machines generate.

NEVER trust a physician who allows his ECG machine to interpret your tracing... run for the door... I'm quite serious about that. If the guy doesn't have the expertise to read your tracing himself, don't trust your cardiovascular health to him.

I've sent people home with ECGs that read ****ACUTE MI***** in large, upper-case font on the top, because the machine was totally, completely wrong. The only thing it's sometimes useful for is in reading QT intervals, and occasionally rate (though the machine can be easily fooled on this one as well).

Have a doc read it, preferably a cardiologist. Of course, if you don't want to pay a guy like that for his expertise you don't have to... but you get what you pay for.

Re:Your wife is correct

[GlassHeart]

I've sent people home with ECGs that read ****ACUTE MI***** in large, upper-case font on the top, because the machine was totally, completely wrong.

I'm obviously not qualified to comment on your clinical diagnosis, but this statement worries me. My expectation as an engineer (but not one of medical devices) is not to replace the professional operating the device, but to supplement him or her in a useful way. That is, if I designed the ECG you use, I would like that 99% of the time it agrees with you, and the 1% of the time that it doesn't you take it so seriously that you consult a panel of specialists. That's my idea of a working man-machine system.

If you regularly ignore its conclusions, then it's better not even having the feature. The one time in a thousand that you're wrong and it's right, you'll ignore it anyway. There's something broken in the system here, in my uninformed opinion.

Re:Your wife is correct

[The Tyro]

No no... I appreciate the input of you guys that actually make the equipment function... the Biomed guys regularly save me (by keeping my equipment running). I couldn't do my job nearly as effectively if it wasn't for the biomedical engineers. I don't mean to make fun of anyone's hard work, and I'm probably being too hard on the people that program these things. Maybe it's the case that the interpretation software is simply in its infancy.

Perhaps I should expand on my initial comments. A previous poster pointed out that the first thing you are taught in medical school is to ignore the machine read... that's true, and medical students are still taught that way (I teach in an academic setting, and I teach my students the same thing).

As I understand the machine's algorithms (if somebody who programs these things wants to correct me, please do), they interpret the waveforms based on an ideal model, and attempt to interpret current-of-injury patterns, based on deviation from an expected baseline.

Many situations make the machine read useless (and to be fair, extraordinarily difficult)... any patient in a paced rhythmn (pacemaker, single or dual chamber), the machine will default, and not give a read. An excellent call for the engineer that designed the machine... reading injury on some paced rhythms can be very sticky, even for an experienced clinician. Some of these machines regularly read "digitalis effect".. a difficult call, particularly in a suspected ischemic or strain-induced ST depression. A noisy baseline (in a patient who's shaking, for instance)will often throw off the machine. Many patients who have known cardiac disease have EKGs that are difficult to interpret, and injury that can only be discovered based on comparison to a previous EKG.

What I'd like to see is a program that compares old EKGs to new ones, and automatically gives you a change summary (in addition to the tracings themselves, naturally). I could see that being very useful, particularly if it uses the previous EKG tracings to redefine "normal" for itself. That might help the over-sensitivity problem. Many people are walking around with tracings that are nowhere near the classic "normal," but are normal for THEM. What I'm saying is that I'd like to see a program with a dynamic "normal;" one it can redefine on the fly.

It's not to say that I don't read the machine's interpretation... I do, but I subordinate it to my own clinical interpretation. To be fair, I have the luxury of knowing the history... something the machine may never know, and as any physician will tell you, history makes the diagnosis 80% of the time; the tests are simply to confirm what you suspected all along.

Maybe if you frame it like that, EKG machine reads don't really need to be perfect... they are, after all, just an adjunct... A human still makes the decisions.

Re:Visual Basic?

[Anonymous Coward]

How to build an ECG for $4:

parts list:

* one surplus patient cable with sensor and plug ($4 on ebay)

instructions:

* Plug the sensor into a strip chart recordor or heart monitor you might have lying around the house. For instance I found and old Hewlett-Packard model 78534C EKG and dual-channel pressure monitor.

You're done! It's THAT EASY! And just FOUR BUCKS!

Tune in next week when I tell you how to build your own x-ray machine for the cost of some X-ray film (you might need to find some medical equipment you might have laying around the house to complete the project).

It seems a bit cheap doesn't it?

[fireboy1919]

I'm going to spring for the $30 ECG.

I learned my lesson with the $4 dentistry set, and even worse, the $4 electroshock therapy machine.

I STILL can't quite get my hair to stop standing on end. I can't even wear hats - hair pokes through like skewers through butter (which, incidentally, is one of the only things I can eat now thanks to the dentistry set).

I thank the lord I didn't invest in the $4 eye-surgery kit.