CMS/DRL and reference with ECG signals

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ipoz
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Joined: Mon Sep 23, 2019 7:21 am

CMS/DRL and reference with ECG signals

Post by ipoz » Mon Sep 23, 2019 8:23 am

Hello!

I am PhD student, using Biosemi ActiveTwo to collect ECG (I have 3 ECG channels on chest), GRS, respiration and temperature signals.

I have some questions regarding i) the preferable CMS/DRL location and ii) reference use in ECG recording?

Re: i) preferable CMS/DRL location:
My understanding is that ECG signals are measured and saved in files with respect to CMS and that referencing is important as valid ECG signals truly appear only after a subtraction step is made, which cancels the CMS out. However, it is said somewhere that CMS should be better placed in the centre of active/measuring electrodes, while DRL should be ideally placed away from the measuring electrodes. Does the CMS/DRL location matters at all and what is the preferable location for CMS/DRL in ECG recording?

Re: ii) reference use in ECG recording:
From previous discussion, it was said that the following three referencing options are possible:
'1. Monopolar: using one active electrodes as a reference, calculate the voltage between every electrode and the reference electrode (V1 = E1-REF, V2 = E2-REF, etc.)
2. Bipolar: select pairs of electrodes and subtract one from the other (V1 = E1-E2, V2 = E2-E3, etc.)
3. Linked reference: Use the average of several electrodes as a reference. Calculate the voltage of every electrode with respect to this reference. e.g. REF = (EA1+EA2/2), then V1 = E1 - (EA1+EA2/2), etc.'

I would instinctively use the option 2 (i.e. bipolar) for ECG signals, by subtracting two of my ECG electrodes located on chest one from the other, as per standard Einthoven Lead I, II or III configurations. However, are any of the other reference options below correct, or are these specific to EEG?
- Example 1 = Monopolar: select one active electrodes as a reference (e.g. a ‘neutral’ electrode located far from the chest, such as ear lobe), and calculate the voltage between every electrode on chest and the reference electrode (V1 = E1-REF, V2 = E2-REF, etc.)
- Example 2 = Linked reference: Use the average of several electrodes as a reference (e.g. Wilson Central Terminal (WCT), defined as the average between Left-Arm, Right-Arm and Left-Leg electrodes), then calculate the voltage of every electrode on chest with respect to this reference.

I guess, because I am only interested on HRV (i.e. RR intervals, not other wave form), any of these reference should reproduce similar results, right?

My last question is regarding the bipolar signals displayed in the ‘bipolar tab’ in software. Are these bipolar signals influenced at all by the reference chosen in the ‘monopolar tab’, or are these just calculated by simply subtracting two ‘raw’ ECG electrodes in software?

Thank you very much for your time.

Best regards, Ilaria

Coen
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Re: CMS/DRL and reference with ECG signals

Post by Coen » Mon Sep 23, 2019 1:42 pm

1) For ECG, locate CMS on the chest. DRL can be anywhere on the body.

2) For hearttrate determination, just use two electrodes on the chest and process the difference (E1 -E2) in your BDF file reader.

3) Bipolar displayed signals are just differences between two raw channels (not affected by reference choice in the monopolar display). Setting in the left sidebar do not affect the data to BDF file.

Best regards, Coen (BioSemi)

ipoz
Posts: 3
Joined: Mon Sep 23, 2019 7:21 am

Re: CMS/DRL and reference with ECG signals

Post by ipoz » Tue Sep 24, 2019 7:51 am

Hi Coen,

Thank you very much for this clarification.

Just a couple of more points:
1) What would be the consequences of CMS placed far from the measuring electrodes (i.e. ECG in this case)?
2) Why a Wilson Central Terminal (WCT), as the average between LA, RA and LL electrodes, is recommended as ECG reference in the Biosemi website? Is this in case of more complex ECG set up, such using precordial plus limb electrodes?

Thank you, Ilaria

Coen
Site Admin
Posts: 980
Joined: Fri Mar 26, 2004 7:00 pm
Location: Amsterdam, Netherlands
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Re: CMS/DRL and reference with ECG signals

Post by Coen » Tue Sep 24, 2019 1:15 pm

1) Higher Common Mode
2) WCT reference offers standardized ECG waveforms

Best regards, Coen (BioSemi)

ipoz
Posts: 3
Joined: Mon Sep 23, 2019 7:21 am

Re: CMS/DRL and reference with ECG signals

Post by ipoz » Wed Sep 25, 2019 12:23 am

Thank you for your reply.

Best regards, Ilaria

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