Removal of motion
artifact from ECG electrodes
Adaptive
Reduction of Motion Artifact: Overview
Heart
disease is the major cause of death in the United States. Holter
recordings and stress tests are important tools for diagnosing heart disease,
but motion artifact in these ambulatory recordings reduces the reliability of
the tests, especially when they are computer assisted. Motion artifact can
also cause false alarms during patient monitoring, which can reduce clinician
confidence in monitoring equipment alarms and, consequently, slow response time.
Two sources can generate
motion artifact: the electrode metal-to-solution interface and
fluctuations in skin potential due to skin stretch. The first source of
artifact has been significantly reduced with modern Ag-AgCl recessed electrodes,
but skin stretch remains a serious problem. Standard methods for reducing
motion artifact due to skin stretch require skin abrasion, but this method has
significant drawbacks: it causes patient discomfort, it results in more
work for the ECG technician, and it can be ineffective for long term recordings.
We have been investigating
methods for using adaptive filters to remove motion artifact from ECG
recordings. An adaptive filter can remove noise from an ECG recording if a
signal is available that is linearly related to the motion artifact, but
contains no ECG signal. The adaptive filter uses noise corrupted ECG and
the signal that is related to the motion artifact to estimate the motion
artifact. This motion artifact estimate is then subtracted from the noisy
ECG, reducing the motion artifact in the resulting signal.
By
placing stretch sensors directly onto ECG electrodes, we have been able to
generate signals that are related to the skin stretch near the electrode and the
resulting motion artifact. We have been able to produce significant motion
artifact reduction using an adaptive filter and these signals. Figure 1
shows a recording of an ECG, the electrode mounted stretch sensor signal, and
the signal that results after the motion artifact has been removed. We are
presently investigating the use of a skin/electrode impedance signal for
adaptive motion artifact removal. An impedance based artifact removal
system has the potential to be less expensive than one based on electrode
mounted sensors because standard ECG electrodes could be used.
Project
History
“Adaptive System for Reduction
of Motion Artifact” was funded by the National Institutes of Health (NIH)
through a Small Business Innovative Research (SBIR) Grant (1R43 HL56504).
Continuing work on “Comparison of Adaptive Methods to Remove Motion Artifact”
is presently being funded under another NIH SBIR grant (1R43 HL63627).
Intellectual
Property
EP Limited has been granted a
patent for “Apparatus and Method for Reduction of Motion Artifact,” Patent
Number 5,978,693.