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Abstract—This paper introduces a pulse oximeter prototype
designed for mobile healthcare. In this prototype, a reflection
pulse oximeter is embedded into the back cover of a smart
handheld device to offer the convenient measurement of both HR
(heart rate) and SpO
2
(estimation of arterial oxygen saturation)
for home or mobile applications. Novel and miniaturized circuit
modules including a chopper network and a filtering amplifier
were designed to overcome the influence of ambient light and
interferences which are caused by embedding the sensor into a flat
cover. A method based on adaptive trough detection for improved
HR and SpO
2
estimation is proposed with appropriate
simplification for its implementation on mobile devices. A fast and
effective photoplethysmogram validation scheme is also proposed.
Clinical experiments have been carried out to calibrate and test
our oximeter. Our prototype oximeter can achieve comparable
performance to a clinical oximeter with no significant difference
revealed by paired t-tests ( for SpO
2
measurement and
for HR measurement). The design of this pulse
oximeter will facilitate fast and convenient measurement of SpO
2
for mobile healthcare.
Index Terms—Heart rate, Arterial oxygen saturation,
Reflection pulse oximeter, Mobile-healthcare
I. INTRODUCTION
ARDIAC and respiratory diseases cause about one quarter
of death around the world according to a report from the
World Health Organization. It also reports that lower
respiratory infection is the top cause of death in low-income
countries, and ischemic heart disease is the top cause in other
countries [1]. It is predicted that three out of four leading causes
of death in 2030 will be cardiac or respiratory diseases [2]..
Heart rate (HR) and peripheral oxygen saturation (SpO
2
) are
two significant vital signs for patients with cardiac or
respiratory diseases [3]. It is believed that many risks can be
detected in daily life if HR and SpO
2
can be monitored quickly
and conveniently [4] especially for babies [11] and chronic
patients.
Manuscript received Feb 06, 2015. This work was supported by National
Nature Science Foundation of China (NSFC) under Grant No. 61271138.
X. Chen* is with the Department of Electronic Science and Technology,
Centers for Biomedical Engineering, University of Science and Technology of
China (USTC), Hefei, 230027,China (corresponding author:
+86-0551-6360-1175; e-mail: xch@ ustc.edu.cn).
Z. Lu, Z. Dong, Z. Zhao and X. Zhang are with the Department of
Electronic Science and Technology, Centers for Biomedical Engineering,
University of Science and Technology of China (USTC), Hefei, 230027,China
(e-mail: luzhiy@mail.ustc.edu.cn, dzf85@ustc.edu.cn, zyzh@ustc.edu,
xuzhang90@gmail.com).
Clinical oximeters are widely used to measure HR and SpO
2
,
which typically measure the transmitted light through tissue
(named transmission pulse oximeter [4]), so that the light
source and receiver are placed on the opposite sides of the
measuring site. As a result, a transmission pulse oximeter needs
to be applied to the body extremity (e.g. fingertip [6] or earlobe)
and it is often designed as a finger clip. Clinical oximeters are
well-designed for inpatient use for long-term monitoring, but
are too large and impractical for outpatient use. Finger clips are
especially inconvenient in daily life. Therefore, it is necessary
to develop small-size portable oximeters towards home or
mobile healthcare. Embedding an oximeter into mobile or
wearable devices is appreciated.
Mobile devices such as mobile phones and personal digital
assistants (PDA) have become more and more powerful and
pervasive in recent years. Their private nature and advances in
computing, storage and wireless network services are leading to
the development of mobile device-based healthcare systems [7].
Many mobile healthcare systems and solutions based on
sensors embedded in mobile devices have been developed [8].
HR [9] and SpO
2
[10] measurement based on the built-in
camera are also being studied, but currently there are no
oximeters based on embedded sensors or oximeters embedded
into mobile devices. In order to provide accurate and
convenient HR and SpO
2
measurement, we aim to embed an
oximeter into a mobile device. By sharing the battery, the
screen and the processor of the mobile device, our efforts can
be considered as an effective way of making oximeters more
portable and flexible. Though several transmission oximeters
have been developed as a mobile device accessory [6] [30],
embedding them into the device is infeasible due to the
requirements of sensor placing (such as a finger clip).
Alternatively, reflection pulse oximeters [4] can measure
reflected light and allow the light sources and receivers to be
mounted side by side on the same plane. They can also work on
various parts of the body [11] including the wrist [12], finger
[13], tragus [14], etc. and offer more advantages for use in
flexible circumstances. Furthermore, they can be easily
embedded into a wrist strap [11], a sensor ring [13], and other
wearable or portable devices. For instance, Y. Mendelson et al.
[15] developed a coin-like wearable reflection oximeter as an
accessory of their mobile device. M. Poh et al. [16] successfully
embedded a reflection sensor into the earphone to measure
heart rate. R. G. Haahr et al. [17] developed a wearable
Electronic Patch with a small reflection oximeter. Since
reflection pulse oximeters can be designed to be very small and
A Prototype of Reflection Pulse Oximeter
Designed for Mobile Healthcare
Zhiyuan Lu, Xiang Chen*, Member, IEEE, Zhongfei Dong, Zhangyan Zhao, Xu Zhang, Member, IEEE