Biomedical Engineering Reference
In-Depth Information
In recent years, some non-contact breath measurement methods are developed. A
study used a CCD video camera to detect the optical flow of the user in bed [19].
PneumaCare [21] developed a non-invasive method called Structured Light Plethys-
mography (SLP), which utilizes the distortion with movement of a structured pattern
of light to calculate a volume or change in volume of a textured surface. Another
study conducted an experiment and the results showed that SLP was comparable in
performance to spirometer [22]. Moreover, slit lights projection [1, 2] is another non-
invasive method which measures the breathing conditions by projecting the near-
infrared multiple slit-light patterns on the user and measuring the breathing status. In
addition to computer vision-based methods, there is a non-contact method which uses
ultra wideband (UWB) to measure the breathing status. A study proposed an applica-
tion of UWB radar-based heart and breathing activities for intensive care units and
conventional hospital beds [24]. Another study used UWB to measure baby's breath-
ing and heart rate especially in terms of opportune apnea detection and sudden infant
death syndrome prevention [31].
For monitoring the sleep activity through movement, actigraphy has been used to
study the sleep patterns for over 20 years. Actigraphy is a non-invasive method of
monitoring human activity cycles [23]. It is useful for determining sleep patterns and
circadian rhythms. The advantage of actigraphy over traditional PSG is that actigra-
phy can conveniently record the sleep activity [3]. In recent years, many commercial
products were developed, such as Fitbit, WakeMate, and Actiwatch. In general, these
products detect the information of time to fall asleep, time to wake up, and totally
sleeping time. A study evaluated the measurement results of actigraphy and compared
to PSG, and the experimental results showed that sleep parameters from actigraphy
corresponded reasonably well to PSG [14]. In addition, there is a non-contact method
which uses a microphone and an infrared sensor to monitor the sleep status [5]. More-
over,
s
ome studies utilize motion sensors (accelerometer, piezoelectric sensor) inside
the pillow [27] or bed [10, 18] to monitor the sleep movement and sleep positions.
However, none of related research in our survey has a complete study to provide a
non-contact and multi-functioning sleep monitoring technique to monitor the sleep
conditions. In this study, we developed a non-contact sleep monitoring system which
can monitor user's sleep position, breathing condition, and body movement in the
same time.
3
System Design
In this study, a cross-section object detection method is proposed to detect user's head
and torso using a depth camera. The sleep position, body movement, and breathing
condition are monitored once the head and torso is detected. The procedure of this
method is as follows: First, the view transformation is estimated. Then, a median filter
is adopted to reduce the image noise after view transformation. Next, a cross-section
method is used to detect user's head and torso so that the sleep position and body
movement can be measured. Besides, a breath measurement method is proposed to
detect the breathing conditions through the movement of the torso.
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