how to develop a 12 lead ECG system using NI Hardware

[aspired]

I would like to develop a 12 lead ECG monitoring system using NI SCXI and DAQ hardware. I should be able to measure lead configurations I, II, III, aVR, aVL, aVF and pericordial leads 1-6.
If you have developed this sort os a 12 lead monitoring system before please email me. thanks

[Andrew Madry]

Dear Aspired



SCXI is great for this sort of biomedical application as there are isolated amplifiers available. We've used the SCXI 1120 isolated amplifier for this purpose. Note this is not suitable for human use. email me and I can send you info on the issues regarding human use.

The issue with 12 lead is that some of the leads are referenced together in a very specific way.
Lead1=VLA-VRA
Lead2=VLL-VRA
Lead3=VLL-VLA
you can connect these as differential inputs. However the referencing of the amplifier has to be considered.
The precordial leads are referenced to what is called the Wilson Central Terminal. Some circuitry is required outside the Amplifier system to set this up.

For human use we've done projects interfacing 3rd party 12 l
ead systems to LabVIEW. This was done through an ActiveX control we developed.

If you need references or assistance feel free to contact me at andrew@madry.com.au or via www.madry.com.au
cheers
Andrew Madry

[aspired]

Hi Andrew,

Thank you for answering my question.

The system we are trying to develop will be used only for non-survival animal experimentation so isolation required, while being important, is not that high..

I have a few questions

1) Is it possible to implement the �summing/subtraction� or �transfer function� of the Instrumentation amplfier in the software.
Meaning that if I have 10 signals coming off the body ( RA, RL, LA, LL, 6 pericordial leads) and each signal is INDIVIDUALLY amplified/conditioned in hardware and digitilized then can I implement the �circuitry for referencing� in Real-time Labview to acquire the 12 Lead configurations ( I, II, III, avR, avL, avF and 6 chest)?.

2) If not why .

3) If yes, if there any disadvantage ?.


thanks again.

[Andrew Madry]

This page from the website of a company that makes bio amplifiers shows exactly how to do it.
www.biopac.com/AppNotes/ah206/wilson.htm

You set up the Wilson Central Terminal using jumpers and with 8 amplifiers, 10 electrodes, you can do the 12 lead measurement.
For example lead II can be derived from Leads I and III in software.
You can do the same thing with amplifiers from NI.
The note explains how to do the jumpering of cables reasonably well and the software calculations required.
You would need to make up a Wilson Central Terminal lead. I believe the Wilson terminal has resistors in the branches. Most texts on ECG Instrumentation describe this.

There shouldn't be any disadvantage. One thing to be careful of depending o
n how the electrodes are connected is something called the half cell potential. This effectively creates a DC offset. Many of the DAQ cards are DC coupled and this makes it difficult to measure the signal required within the dynamic range of the card. This can generally solved by AC coupling, which some cards have. If not you can make up a simple resistor & capacitor high pass filter.