2 finger ECG circuit

[Mozart7]

Hello everyone. I am currently doing a personal ECG project. I would like to design a two electrode portable ECG that I can bring around. I followed this circuit from cs.washington.edu (credits to them) .

I have attached the photo with this post. I am unable to get any ECG wave from the circuit. I seem to be getting baseline drifts when I put my fingers on the electrode. I hooked up the circuit to an Arduino uno and adafruit tft board. The arduino and lcd work fine. I do not understand how the circuit functions and what mistake am I making. please help. Thank you in advance.

 

[audioguru]

Look at the ECG circuit on the datasheet of an AD620 instrumentation amplifier IC. It measures the heart electrical pulses with the probes near the heart, not on the fingers. It cancels baseline DC drift (caused by movements from other muscles including the lungs) by adding inverted common mode signals picked up by both probes and feeding this cancellation signal to the leg of the patient. It doesn't need a notch filter because it cancels leakage 60Hz hum that is picked up by the patient.


I have had a few ECG tests and always had the probes on my chest, not on my fingers and not on my arms. The cancellation signal cancels any AC or DC signal that is the same on both probes and mine was on my chest, not on my leg.

 

[jpanhalt]

That is not an unheard of technique: https://www.hindawi.com/journals/cin/2011/720971/

Of course, the signal may have a lot more noise and be more difficult to interpret.

John

 

[audioguru]

Mozart7 said nothing about using a finger on each hand. I assumed he used two fingers on one hand.
I guess a woman would not like to have the electrodes on her breasts (the probes might not pick up heart signals from the breasts anyway) so maybe the thumb tips would work if the electronics can get rid of the noise.

 

[Mozart7]

Hello everyone, I'm really grateful for all the replies! Thank you so much! I'm really interested in this portable two finger ECG machine because there aren't many out there and besides its fun to make one yourself. Once I get back from work I can post my circuit and the resulting oscilloscope reading! Is there any way i can improve on this circuit to give a better ECG without noise distortion?

That is not an unheard of technique: https://www.hindawi.com/journals/cin/2011/720971/

Of course, the signal may have a lot more noise and be more difficult to interpret.

John

Interesting read! From reading that article I believe I am on the right track in building a finger ECG. It is amazing that ECG measured from the fingertips have such potential. There is a product called Alivecor ( https://www.alivecor.com ) that measures ECG from the fingers.

Mozart7 said nothing about using a finger on each hand. I assumed he used two fingers on one hand.
I guess a woman would not like to have the electrodes on her breasts (the probes might not pick up heart signals from the breasts anyway) so maybe the thumb tips would work if the electronics can get rid of the noise.

Hi again audioguru! I used one thumb each for the two electrodes.

 

[large_ghostman]

2 finger wont tell you much of anything sorry. The heart is complex electrically, partly your looking at around 5-6 things. For a start it isnt just the existence of the QRS complex but the duration and relation to the P wave, then you have the axis in degrees from the P wave to the QRS complex.

So without giving you a Biology lecture look at it like this............
The various parts of the ECG are made up of electric waves, just a single complex tells you ZERO! If you have a single finger or two finger system you have NO way to work out the axis the signal has come from, so you cant for the P wave for a start. NO P wave means the QRS complex is meaning less. The reason you have 6 and 10 lead ECG's is so each type of wave form can be captured, this then gives an accurate picture of the hearts finger print.

All the links I can give you are going to need a good understanding of Biology, the only real way to get it is to read a book, you need a book on interpreting ECG's, from that you can work out how and why you need more than two leads.

This link is not that good, but its a pretty basic level and should give you an idea why two finger systems are rare.

https://geekymedics.com/how-to-read-an-ecg/

This link tells you about the axis, its done by time base measurement, in other words the pickup near the heart detects the signal start, it then depends if lead III or IV (I think its II &IV but i am rusty) is the first to pick up the signal, this tells you what axis (direction/path) the signal traveled, this is critical to know for many abnormalities. But read the links to get a idea WTF i am on about.

https://lifeinthefastlane.com/ecg-library/basics/axis/

EDIT
Told you I was rusty, I got my leads wrong!!! the VF lead sends (the pad near the heart) III and IV dont relate to axis.....Like I said its complex and I only do biology for fun

 

[jpanhalt]

I think you have entirely missed the intent of the TS.

Here is a classic:

1) What is it? (Please don't do a Google image search.)
2) Why wouldn't a 2-finger ECG diagnose it? (I would suggest the TS try two index fingers instead of the two thumbs, but that is an empirical decision to make. Either would probably work for the purposes of the TS.)

 

[large_ghostman]

I see two things wrong, one is a Asymmetrical type 2 block and partial P wave. That is no 10 lead for sure though, you cant tell which axis the signal is from so no idea if its F or A origin. Now can I go google?

 

[large_ghostman]

So now have googled,

To understand my answer read causes

 

[large_ghostman]

BTW yes two finger might catch the block, but would not give type, but no way two finger or 4 lead would detect P wave abnormality like that.

Just so you know I am not a smart A@@@, i know about ECG's because as one member is aware I have been working extensively on something to do with EEG's, the only way I could begin to understand what I needed to do, was to look into how ECG's work.

So I have spent ALOT of hours on med sites doing the ECG tests etc and trying to understand how the waves are produced and detected. When it comes to the brain, understanding how the heart works electrically helps alot when designing what I am working on.

This is/has been a really long project and I am a long way from finished.

 

[jpanhalt]

No one in his right mind would propose a two-finger ECG to replace a complete one. What you don't seem to understand is the benefit of such screening, particularly in cultures that frown upon particularly clad women or men in public.

 

[large_ghostman]

But everything that kills you without warning will show as fine on a two finger. Two finger is just like a chocolate fire guard, yes it will stop things coming out the fire, until you light it. The rhythm you see on a single finger one with IR heart rate etc is a partially made up signal.

thats why the first thing they do if you dont get a fully formed QRS complex is a 4 lead in the ambulance. Two finger ECG has no practical use except when you got other signs like holding your arm, sweating alot and laying on the ground. At which point I wouldnt waste time hooking it up anyway. Seriously though if this is for reasons of modesty then it would be better to educate in healthy living. A trace like the one you posted will get you a 10 lead trace no matter how modest you are.

Otherwise how they going to tell which Branch has the block? I recognized it as a type 2 but no way could I tell it was A sided, and in the answer given they dont say witch branch, simply because no way to tell unless your on 10 leads.
The whole point of the ECG is to measure current going both to and away from the heart, and also which side and what direction. How on earth you going to do that with 2 reference points? At best you can give a lucky guess on quadrant with a 4 lead, but two leads??? no chance

As an example, a simple side deviation, explain how that can be seen with two leads effectively on the same plane.

 

[jpanhalt]

2 finger wont tell you much of anything sorry.

But everything that kills you without warning will show as fine on a two finger.

Which is it? Confused? Maybe Google has the answer.

 

[large_ghostman]

Ah I see your confusion... Sorry my assumption was I had elucidated enough information for my meaning to be clear.

Defects within the heart that normally kill quickly, and without much warning. Will give a reading that tells you that there is nothing wrong. Hence they will show you everything is fine.

So as its likely that is still going to cause confusion, allow me to present it this way.
Two finger system will not be able to pick up many very serious conditions, alot of these conditions kill extremely quickly and with little advanced warning.

The following may be a little out of date, the research behind this was done nearly a year ago. I am aware of a better system in the west, however lets assume the slightly older single finger system, is still in wide use (I am pretty sure it is). The OP would actually be better going with the system that UK ambulances use, this consists of a single finger grip, placed on one finger with a Red Led/IR Led and conductive surface inside.

The signal looks good on the screen and the system is actually pretty clever, it is also much more accurate than a two finger system. the way it works (purely from the Heart trace view point), it detects when the heart contracts, the Leds see the change in colour. This acts as the signal to start the start the counts etc, the conductive surface then times how long until the electrical impulse reaches it. In reality it does alot more than this, but the difference between these systems is, the single finger one has a known start point and time, from this a reasonable QRS can be calculated, then when the heart muscle relaxes this is detected again by the colour change within the blood vessels and the P wave (maybe some of the T as well) can be calculated.

Its not ideal which is why they carry a 6 lead system in the UK as well, the single finger is quick and easy, it will also alert them to a abnormal QRS. So I ask again, how can a system laying on the same plane and working purely electrically, detect the same thing?

I am aware you dont like poor grammar and I apologize for that, However i am also aware you are intelligent enough to have worked out what I meant. It might be worth keeping in mind that I am now 17, I no longer bite as i used to do. You are welcome to try and belittle me, your welcome to point out spelling and grammar errors. The fact remains you cant really argue against what I was saying.

OP
If this is for modesty reason, then i suggest this is likely not for a hospital situation?? If this isnt for a hospital situation, then i would recommend looking into single finger systems. If you need access to material that explains the function and mechanism behind a ECG, then please feel free to PM me. I have a great deal of information on ECG systems and theory of operation, you are welcome to some of the books and papers (pdf's).

 

[audioguru]

I have had ECG's done in the hospital and in the doctor's office. They all used many (6?) leads on my chest. I wore a portable ECG machine for a few days but I can't remember how many leads it had. I joked that it detected my wife and I "fooling around".
In the hospital I had a optical device on a finger but it simply counted heartbeats and beeped for each one. It would probably scream an alarm if it detected no beats. Maybe it detected the oxygen concentration in the blood?

 

[large_ghostman]

I have had ECG's done in the hospital and in the doctor's office. They all used many (6?) leads on my chest. I wore a portable ECG machine for a few days but I can't remember how many leads it had. I joked that it detected my wife and I "fooling around".
In the hospital I had a optical device on a finger but it simply counted heartbeats and beeped for each one. It would probably scream an alarm if it detected no beats. Maybe it detected the oxygen concentration in the blood?

Hi AG
67 leads is also known as a 10 lead, it would be more accurate if they called them quadrants!! Several cables go back to a single lead, and the portable one can give them a good idea what your doing . Loads of different single finger ones, the type you describe sounds like its just the LED one, that does work simply from change in blood colour, they are actually pretty clever! In most countries (except the UK), if the beep stops then yes they come and help. Here they just turn alarm off .

My interest is actually EEG machines, but I found it easier to start at the ECG machine, From memory you mentioned alot of helpful stuff with buffering the signal in that thread. I didnt update the thread, but the project is still on going and will be for some time.

 

[audioguru]

Yes in my local hospital if the beep stops they page Code Blue and they all come running to help the cardiac arrest patient.
My heart attack was "only" caused by two blocked heart arteries that they stented quickly so that there was no damage to my heart or brain. Then I was the fittest and one of the oldest of all patients in the following recovery exercise classes.

 

[large_ghostman]

Here they just shout, hes gone blue get a coffin lol.