Influence of Motion Artifacts on Photoplethysmographic Signals

脉搏波 运动干扰

International Conference on Control, Automation and Systems 2008 Oct. 14-17, 2008 in COEX, Seoul, Korea

Influence of Motion Artifacts on Photoplethysmographic Signals

for Measuring Pulse Rates

Yunjoo Lee, Hyonyoung Han, and Jung Kim

School of Mechanical, Aerospace & Systems Engineering, Department of Mechanical Engineering,

Korea Advanced Institute of Science and Technology, Daejeon, Korea

( Tel : +82-42-869-3271; E-mail: rosela@kaist.ac.kr , hhn98@kaist.ac.kr , Jungkim@kaist.ac.kr)

Abstract: One of the most important issues in the wearable healthcare sensors for continuous monitoring in daily life is motion artifact reduction. This paper presents an analysis of motion artifacts on PPG signals to find the suitable location for monitoring heart rates. The experiment system, which consists of PPG sensors and data acquisition system, wasbuilt to measure heart rate during controlled body motions such as walking. A reflective type PPG sensor was used to measure the pulse rate signal from several locations of the body including forehead, ear, neck, wrist, finger, and toe,and data were collected and analyzed to compare the effects of motion artifacts on signals. Pulse rates were estimated by counting the number of heartbeats in minute and comparing results with from the two states of stationary and moving conditions. The experiment results showed that forehead is the most suitable location for monitoring because ithas less motion artifact than other locations. These results can be used to support the measurement of pulse rates to detect clinically significant heartbeat problems.

Keywords: Photoplethysmography(PPG), motion artifacts, heart-rate monitoring

1. INTRODUCTION

Photoplethysmography (PPG) sensors for measuring pulse rates have received significant attention in recent years due to their ease of integration with wearable healthcare sensors. PPG is an optical measurement technique that can be used to detect volumetric changes of the blood stream through vasculature. This sensor consists of an infrared light emitting diode (LED) and a silicon photodiode. Light emitted by the LED is partially reflected, transmitted by the skin, surrounding tissues, and the blood before it reaches the photodiode [1]. The advantage of the PPG technique is that only two components are required, thereby greatly simplifying the optical sensor and miniaturization of the sensor system.

There are previous studies on the PPG signal for obtaining the information of pulse rates and analysis of the pulse wave in blood vessels[2]. Regional variations in skin are the main reasons for the difference in signal quality observed at various locations. In recent years, different positions of the sensors have been studied extensively including body locations such as finger [3], wrist [4], brachia [5] and belly [6]. For commercial clinical sensors, it is also common to use ear and forehead [7] as the anatomical regions of interest. Additionally, Tur et al.[8] compared the measurement of the basal perfusion of the cutaneous microcirculation as a function of anatomical position using noninvasive PPG. The results from the study showed that anatomical locations such as the finger, face or ear have a higher cutaneous perfusion in comparison to other locations. However, these studied did not consider the effect of motion on signals during movement.

Motion artifact reduction is the most challenging issue in wearable healthcare sensors including PPG due to body movements. Motion artifacts on signals are considered as the relationship between motion and noise. This includes voluntary and involuntary movements of the interface between the sensor and tissue. This effect is minimized by increasing the field of view of the light and detector. Although sensing components are physically changed to decrease motion artifacts, more analysis is needed to determine which sensor location is the best for monitoring heart rates. To select a suitable location, features such as clinical acceptability with high signal quality in monitoring were considered. The aim of this study was to determine location in the body which has the least motion artifacts from different location signals.

The organization of this paper is as follows. Section2 describes the device: the sensor type, experimental setup and procedure are explained. Experimental results are described in section 3; counting the number of pulses in a minute to acquire heart rates and comparing results from the two states of stationary and moving conditions. Finally, results are discussed and the paper is concluded

in section 4.

Fig.1. Corrupted signal due to motion artifact

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