Reduction of Motion Artifacts and Improvement of R Peak Detecting Accuracy Using Adjacent Non-Intrusive ECG Sensors

Abstract

Non-intrusive electrocardiogram (ECG) monitoring has many advantages: easy to measure and apply in daily life. However, motion noise in the measured signal is the major problem of non-intrusive measurement. This paper proposes a method to reduce the noise and to detect the R peaks of ECG in a stable manner in a sitting arrangement using non-intrusive sensors. The method utilizes two capacitive ECG sensors (cECGs) to measure ECG, and another two cECGs located adjacent to the sensors for ECG are added to obtain the information on motion. Then, active noise cancellation technique and the motion information are used to reduce motion noise. To verify the proposed method, ECG was measured indoors and during driving, and the accuracy of the detected R peaks was compared. After applying the method, the sum of sensitivity and positive predictivity increased 8.39% on average and 26.26% maximally in the data. Based on the results, it was confirmed that the motion noise was reduced and that more reliable R peak positions could be obtained by the proposed method. The robustness of the new ECG measurement method will elicit benefits to various health care systems that require noninvasive heart rate or heart rate variability measurements.

Adaptive Noise Reduction Algorithm to Improve R Peak Detection in ECG Measured by Capacitive ECG Sensors

“…In recent research [6], four cECG sensors were mounted in a row on the back of a chair and driver’s seat (Figure 1). Conductive fabric was placed on the bottom of the seat and connected to a driven right leg circuit to reduce the common noise component of the measured ECG.…”

“…cECGs $si{g}_L$ and $si{g}_R$ were obtained from the two sensors outside in a row and additional cECGs $si{g}_{aL}$ and $si{g}_{aR}$ were obtained from two other sensors, which were close to the center. This study used signals that were defined and used in the existing research [6]. The difference between $si{g}_L$ and $si{g}_R$ is filtered through a band pass filter (BPF) with a 0.05–35 Hz pass-band; this was defined as a measured ECG ($EC{G}_m$): $EC{G}_m=\mathrm{BPF}\left(s,i,g_L,-,s,i,g_R\right).$…”

“…For example, ECG measurement cannot be easily performed while driving, but evaluation of a driver may be necessary to prevent emergency situations that can be caused if a driver has a heart attack or falls asleep while driving. Therefore, cECG sensors could be mounted into the driver’s seat to obtain ECGs of drivers [6,7,8]. …”

“…Recently, new reference signals obtained from additional cECG sensors were suggested to reflect the characteristics of the motion noise but not the bioinformation [6]. ANC using the new reference signal was verified to improve R peak detection by comparing the proposed algorithm to previous algorithms.…”

Advanced carbon materials for flexible and wearable sensors

“…Recently, flexible sensors have attracted increasing attention due to their great potential applications in wearable electronics and intelligent systems [1][2][3][4][5][6][7][8][9][10]. Particularly, flexible sensors can be mounted on human body or clothing for continuously monitoring subtle and large human motions [11][12][13][14] and physiological information, such as phonation [15], pulse [16][17][18], electrocardiogram (ECG) [19][20][21], respiration [22,23], skin temperature [24,25], and so on. Towards these applications, wearable sensors should have some basic characteristics, such as high sensitivity, good flexibility, desirable stretchability, biocompatibility and good stability.…”