Biomedical Engineering Reference
In-Depth Information
while sleeping [11, 20, 30], as well as estimate the sleep cycle and evaluate the sleep
quality. For breath measurement while sleeping, it is important and mainly used to
detect the symptom of sleep apnea. Sleep apnea is one of the most important sleep
disorder characterized by abnormal pauses in breathing or instances of abnormally
low breathing during sleep. For decades, the breath measurement methods would
direct contact to the user while monitoring, and it might interfere with the user and
affect the sleep quality. Although some non-contact breath measurement methods are
proposed in recent years, such as ultra wideband (UWB) and structured light plethys-
mography (SLP), these still have some measurement limitations. For sleep position, in
order to prevent the sleep apnea, studies show that side-lying position is the best
sleeping posture for individuals with sleep apnea [8, 12, 16, 26]. A study analyzed six
common sleep positions, and concluded that supine positions were more likely to lead
to snoring and a bad night's sleep [13]. However, to date, there has been relatively
little research conducted on the measurement of sleep positions.
In this study, a sleep monitoring system using a depth camera was proposed to
monitor users' breathing rate, body movement, and sleep position while sleeping.
Moreover, we evaluated the measurement accuracy of the system, including the accu-
racy of head and torso detection, breath measurement (compared to the RIP), and
sleep movement (compared to Actigraphy). Through the experimental results, we
confirmed that the system could accurately monitor user's sleep conditions. This pa-
per is structured as follows: The first section deals with the introduction of present
sleep studies. The second section of the article is a review of several breath measure-
ment methods and activity monitoring while sleeping. The proposed system design is
described in the third section. The experimental results are demonstrated in section
four followed by the discussion on some important findings. Finally, conclusion and
suggestions are given for further research.
2
Related Work
Breathing is important while sleeping. There are many breathing-related sleep disord-
ers, such as apnea and hyperventilation syndrome (HVS). Currently, many methods
are proposed to monitor the breath conditions while sleeping. Most screening tools
consist of an airflow measuring device, a blood oxygen monitoring device, and the
respiratory inductance plethysmography (RIP). Thermistor (TH) measurements have
been traditionally used to determine airflow during PSG studies. It is placed over the
nose and mouth and infers airflow by sensing differences in the temperature of the
warmer expired air and the cooler inhaled ambient air. However, low accuracy in
detecting hypopneas is a major drawback [4]. The pulse oximeter is a medical device
that monitors the oxygen saturation of user's blood, and changes in blood volume in
the skin. Low oxygen levels in the blood often occur with sleep apnea and other respi-
ratory problems [9]. Respiratory Inductance Plethysmography (RIP) measures the
body movement of chest wall or abdominal wall caused by breathing exercise [7, 29],
and then the breathing conditions can be estimated accurately. However, most of the
breath measurement methods are essential to directly contact to the user while mea-
suring, and it might affect the user and decrease the sleep quality.
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