EKG/pulse wave artifact on EMG signals

[Stavros Zanos]

Hi all-

In analyzing some (intramuscular) EMG signals I have
acquired, I noticed quite pronounced EKG/pulse wave artifacts. Each
muscle has been implanted with 3 wires, and therefore there are up to 3
EMG signals per muscle. However, bipolar EMG derivations do not always
get rid of the artifacts, as different EMG wires are implanted in
different parts of the muscle, and some of them happen to be closer to
arteries than others.

The amplitude of the pulse wave artifact is comparable to low-level EMG activity; its duration is ~300msec.
Conventional smoothing/filtering does not solve the problem.
Identifying the timing of, and removing, these artifacts in the absense
of EMG activity is easy; it gets tricky during EMG activity though, when the artifact gets buried inside the EMG signal.

Is there any (automated) way of removing these
artifacts?  I've thought of performing PCA on all single-ended EMG
signals, making sure one of the first few PCs captures the artifact, and then removing the back-projection of that PC from the original EMGs.
This method has worked for me in the past with removing artifacts from
EEG signals.  The potential problem I foresee with that approach with
EMGs is that it relies on simultaneous recording of the artifact on many channels.  In the case of EMGs however, the timing of the pulse
artifact is slightly different for different EMGs/muscles; for example,
an EMG signal from a proximal muscle will capture the pulse wave earlier than an EMG signal from a distal muscle.

Many thanks in advance
for any insight.

Stavros Zanos, M.D.
University of Washington
School of Medicine
I-413B, WaNPRC
206-6168729
zanos at u.washington.edu

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