Orbital Research Comparison of ECG Signal Quality between a Novel Dry Electrode and a Standard Gel Electrode - Manual

Abstract
BACKGROUND: Electrocardiography has an important role in diagnosis and monitoring of patients. Surface
electrodes relay signals from the patient to the electrocardiograph device. Traditionally gel based electrodes are
used to transmit the electrical signal. However, gel electrodes are inconvenient because they require aggressive
skin preparation and use an electrolytic solution to ensure electrocardiograph (ECG) quality. The purpose of this
study was to compare the reliability and signal quality of traditional gel electrodes with a novel dry electrode that
requires no abrasive skin preparation or electrolytic solution. The dry electrode is designed with micro-anchors
that may penetrate the SC layer of skin. The micro-anchors are intended to reduce motion artifact, increase patient
comfort and maintain signal quality relative to traditional electrodes. The sensing element, housing and snap are
monothilic polymer plated with Ag/AgCl- for conductivity. A novel adhesive scheme is used to maintain the dry
electrode skin interface. The tape is clear, flexible and breathable. SUBJECTS: Eleven apparently healthy subjects
consisting of 6 males and 5 females volunteered as subject (30.25 +/- 7.8 years). All subjects signed a consent form
approved by the Cleveland State University Institutional Review Board. METHODS: Resting and exercise ECGs
were obtained using standard ECG telemetry equipment (ScottCare TeleAdvantage System-Cleveland, Ohio).
Subjects were tested on two consecutive days, wearing either the novel dry electrode or the standard 3M Red dot
electrode in a lead II configuration. The electrode testing was done in randomized sequence. Data was collected
while supine, standing and during a sub-maximal Bruce protocol (GXT). ECG signals for the entire data set were
collected at 120 Hz and were analyzed using the Matlab 6th order Debauchy wavelet technique to de-noise the
traces and establish a signal to noise ratio. RESULTS: A two tailed paired t-test was performed on the signal to
noise ratios to compare the signal quality of the two types of electrodes. The mean signal-to-noise ratio was 16.33
(±2.68) for the standard gel electrode and 17.29 (±2.06) for the dry electrode with a non-significant difference (P
value of 0.2573). CONCLUSIONS: It was concluded that the novel dry electrode provided signal quality that was
comparable to the standard gel electrode without the need for skin preparation or electrolytic solution. The novel
dry electrode may be a suitable alternate to gel based electrodes for the ECG studies. Additional studies are
pending to exploit the fidelity of the novel dry electrodes in more chronic applications.
Comparison of ECG Signal Quality between a Novel Dry Electrode and a Standard Gel Electrode
Kenneth E. Sparks, Ph.D., Cleveland State University (Cleveland, Ohio)
Aaron T Rood, MA Orbital Research Inc (Cleveland, Ohio)
Purpose
The purpose of the study was to compare the ECG signal quality of a novel dry recording electrode to the signal
quality of a standard gel based electrode during graded exercise testing.
Introduction
Surface electrodes relay signals from the patient to the
electrocardiograph device. Traditionally, gel based electrodes
are used to transmit the electrical signal. However, gel
electrodes are inconvenient because they require aggressive
skin preparation and use an electrolytic solution to ensure
electrocardiograph (ECG) quality. Many efforts have focused
on developing an alternative technology to be used for long
duration bio-potential studies for ECG monitoring. As far back
as the 1960’s scientists and engineers attempted to develop dry
electrodes for ambulatory studies.
1-3 Orbital Research Inc.
(Cleveland, Ohio - ORI) has developed a disposable dry
electrode (Figure 1, Figure 2). The success of the technology is
largely due to surface micro-structures that function as the
sensing element of the electrode. These micro-features
augment the electrode/skin interface by mechanically
connecting the skin and the electrode, thus facilitating the
transmission of the ECG signals from the body through the
electrode and reducing motion artifact .
Methods
A repeated measures design was used to test the hypothesis stating no differences in signal quality using the novel
dry electrode when compared to a standard gel electrode during graded exercise testing. Eleven healthy subjects (6
males, 5 females) were telemetrically monitored using the Scott Care Tele Rehab (Cleveland, Ohio) system during a
standard Bruce treadmill protocol. The subject’s age ranged from 21 to 43 years. All subjects followed the protocol
until they reached 85% of predicted maximum heart rate.
The novel dry ECG electrode technology was compared to the standard 3M Red Dot electrode. The electrodes
were tested in random sequence on consecutive days. A permanent marker was used to mark the skin prior to the
first trial to ensure consistency of electrode placement. The 3M Red Dot™ (a gel-based traditional electrode) or the
Orbital Research dry electrode was placed in a LEAD II configuration, without any skin preparation.
Signal was collected at 120 Hz during each trial. The data was analyzed in Matlab™ (The MathWorks Inc. Natick,
MA) using a 6 th order Debauchy wavelet technique to de-noise the traces (Figure 3 ) and establish a signal-to-noise
ratio for each electrode style , mean signal-to-noise ratios (dB) were calculated and comparisons were made using a
paired t-test, at a significant level of 0.05.
Results
The signal quality of the two types of electrodes (Table 1) indicated a mean signal to noise ratio was 16.33 ±2.68 for
the standard gel electrode and 17.29 ±2.06 for the dry electrode with a non-significant difference (P value of 0.2573).
Individual subject results (Figure 4) show variability between the two electrodes between and among subjects.
References
1 . C. W. Patten, F. B. Ramme and J. A. Roman. DRY ELECTRODES FOR PHYSIOLOGICAL MONITORING. NASA-
TN-D-3414 May 1966
2. P. C. Richardson, F. K. Coombs, and R. M. Adams. Some new electrode techniques for long-term physiologic monitoring.
Aerosp Med, vol. 39, no. 7, pp. 745-50., 1968.
3. A. Lopez, Jr. and P. C. Richardson, "Capacitive electrocardiographic and bioelectric electrodes," IEEE Trans Biomed Eng,
vol. BME-16, no. 1, p. 99, 1969
A 6 th order Debauchy wavelet was chosen and using MATLAB, the signals were de-
noised. The cleaned signal was superimposed over the original signal to show the
result of the de-noising. The noise was calculated at every instance as the difference
between the cleaned signal and the original signal. The Signal to Noise Ratio (SNR)
was defined as follows:
( )
) (
) var(
) var(
log 10
) (
log 10
2
2
dB
Noise
Signal
Noise
Signal
SNR ⎟⎟⎠
⎞
⎜⎜⎝
⎛
⋅ =
⎟⎟⎠
⎞
⎜⎜⎝
⎛
⋅ =
σ
σ
Figure 2. A 6 th order wavelet technique.
Yes Yes
Passed normality
test (alpha=0.05)?
0.62 0.80 Std. Error
± 2.06 ± 2.68 Std. Deviation
17.29 16.33 Mean
20.69 20.76 Maximum
19.39 18.09 75% Percentile
17.21 16.79 Median
15.68 15.09 25% Percentile
13.66 11.84 Minimum
11 11 Number of values
ORI
RED
DOT™
COLUMN STATS
Table 1. Signal-to-noise ratio (dB) values.
1 2 3 4 5 6 7 8 9 10 11
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
Red Dot
Dry Electrode
Subject Number
SN
R
(d
B)
Figure 4 Within Subject Comparison of Signal to-to-noise ratio (dB)
Acknowledgements
Orbital Research’s dry electrode development has been funded through the National Institutes of Health,
National Science Foundation and the State of Ohio.
Summary and Conclusion
It was concluded that the novel dry electrode provided signal quality that was comparable to the standard gel
electrode without the need for skin preparation or electrolytic solution. The novel dry electrode may be a suitable
alternate to gel based electrodes for the ECG studies. Additional studies are pending to exploit the fidelity of the
novel dry electrodes in more chronic applications.
Figure 1 Photo Graph of the Novel Dry Electrode
Figure 2. Dry Electrode in place on the skin