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Sleep monitoring and wearables : a systematic review of clinical trials and future applications (Preprint)

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Abstract

BACKGROUND Sleep disorders are a major public health issue. Nearly one in two people will experience sleep disturbances during lifetime with a potential harmful impact on well-being, physical and mental health. The rise of connected objects is bringing new opportunities in sleep monitoring. OBJECTIVE To better understand the clinical value wearables-based sleep monitoring, we conducted a review of the literature, including feasibility studies and clinical trials on this topic. METHODS We searched PubMed, PsycINFO, ScienceDirect, the Cochrane Library, Scopus, and Web of Science up to June 2017. We created the list of keywords based on two domains: wearables and sleep. We used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses to identify, select, and critically appraise relevant research while minimizing bias. RESULTS The initial research collected 255 articles. 18 articles meeting the inclusion criteria were included in the final analysis. Out of the selected articles, four categories appeared. Feasibility studies propose testing new connected tools during sleep, on small samples of subjects. Population comparison studies propose to evaluate the sleep of patients compared to that of healthy subjects. Several studies evaluated connected objects in comparison with polysomnography, a reference test in sleep assessment. Finally, an article evaluates the impact of sleep disorders in the clinic. CONCLUSIONS We conducted a broad analysis of studies on the clinical and technical aspects of the use of wearables for sleep monitoring. This review of the literature showed that wearables are acceptable and promising monitoring tools in a wide range of clinical applications for sleep monitoring.
Sleep monitoring and wearables : a systematic review of clinical trials and future
applications.
Elise Guillodo1, Christophe Lemey1,2,3, Mathieu Simmonet2, Juliette Ropars4,5, Sofian Berrouiguet1,2,3
1. Department of Psychiatry and Emergency, University Hospital, Brest, France.
2. IMT Atlantique, Lab-STICC, F-29238 Brest, France
3. SPURBO EA 7479, Université de Bretagne Occidentale.
4.Laboratoire de Traitement de l'Information Médicale, INSERM, UMR 1101, Brest, France.
5.Department of Child Neurology, University Hospital of Brest, Brest, France
Background
Sleep disorders are a major public health issue. Nearly one in two people will experience sleep
disturbances during lifetime with a potential harmful impact on well-being, physical and mental
health. The rise of connected objects is bringing new opportunities in sleep monitoring.
Objective
To better understand the clinical value wearables-based sleep monitoring, we conducted a review
of the literature, including feasibility studies and clinical trials on this topic.
Methods
We searched PubMed, PsycINFO, ScienceDirect, the Cochrane Library, Scopus, and Web of Science
up to June 2018. We created the list of keywords based on two domains: wearables and sleep. We
used the Preferred Reporting Items for Systematic Reviews and Meta-Analyses to identify, select,
and critically appraise relevant research while minimizing bias.
Results
The initial research collected 255 articles. 18 articles meeting the inclusion criteria were included
in the final analysis. Out of the selected articles, four categories appeared. Feasibility studies
propose testing new connected tools during sleep, on small samples of subjects. Population
comparison studies propose to evaluate the sleep of patients compared to that of healthy subjects.
Several studies evaluated connected objects in comparison with polysomnography, a reference test
in sleep assessment. Finally, an article evaluates the impact of sleep disorders in the clinic.
Conclusions
We conducted a broad analysis of studies on the use of virtual reality in patients with eating
disorders. This review of the literature showed that virtual reality is an acceptable and promising
monitoring tool in a wide range of clinical applications
1.Introduction
Sleep disorders
Sleep disorders are a major public health issue. Nearly one in two people will experience sleep
disturbances during their lifetime (1) with a potential harmful impact on well-being, physical and
mental health (2). The International Classification of Sleep Disorders distinguishes the following
six categories: insomnia, sleep-related breathing disorders, central hypersomnia, circadian rhythm
disorders, parasomnias and sleep-related motor disorders (3). For example, insomnia is
characterized by complaints about the duration and quality of sleep, difficulty falling asleep,
nocturnal awakenings, early awakening and / or non-recuperative sleep (4). This symptomatology
must be present at least three times a week, for at least one month, with negative consequences on
the next day. Sleep and mental health are highly related, with many mental health problems also
being associated with sleeping disorders (5). Traditionally, sleeping disorders have been viewed as
a consequence of mental health disorders, and evidence also suggests that sleeping disorders can
contribute to the development of new mental health problems (6).
Sleep Monitoring
Normal sleep is characterized by a succession of four to six cycles lasting about ninety minutes.
Each of these cycles consists of slow-wave phases and rapid eye movement (REM) sleep, which are
related to slowdown and activation of the central nervous system. During REM sleep, or stage 5,
rapid eye movements are observed and muscle tone is abolished. The early-night cycles are
especially rich in deep, slow sleep and the latter in REM sleep (7). The duration of normal sleep
varies between six and ten hours, depending on several factors, the most important of which are
age and genetics.
Normal and pathological sleep can be explored either subjectively, i.e. by asking the subject, or
objectively, using sensors. An epidemiological study conducted in 2013 with over 1000
participants found a subjective prevalence of insomnia of 15%, while the objective prevalence
measured by polysomnography (PSG) was 32% (8). To date, polysomnography remains the gold
standard to objectively assess sleep characteristics. The polysomnograph plots a hypnogram,
integrating data from several sensors: electroencephalogram (EEG), electromyogram (EMG),
electrooculogram (EOG), thoracic movement (from belts on the chest and abdomen), airflow
measures, oximetry, and electrocardiogram (ECG). The sleep stages are scored according to
standard visual criteria based on the EEG, EOG, and EMG sensors (5). The assessment must be
carried out under controlled conditions in the laboratory for eight to twelve hours. An automated
hypnogram analysis is possible, but still needs manual integration of data (7). Successful recording
of the polysomnography over the course of the recording and the analysis of the results must be
carried out by a clinician with expertise in sleep pathologies in brain disorders. Although
polysomnography is considered the "gold standard", it is an examination with limitations: it can be
cumbersome for the patient, not very accessible, and not being realized in ecological conditions. It
may therefore not be suitable for all populations of interest, such as individuals who are suicidal,
sensitive to the environment or who may require emergency care.
Wearables and eHealth
Increased adoption of features of the internet has increased the possibilities for improved patient
monitoring. Integration of smartphones and wearables tools into medical practice has heralded
the electronic-health (eHealth) and mobile-health (mHealth) era. These tools can be used to self-
monitor or self-assess, allowing individuals to better understand their behavior and body, and
therefore their health. Aspects of daily life are particularly targeted, with measures of diet,
physical activity or sleep. These self-measurements can be tracked and analyzed with the objective
of modifying individual behaviors, including using educational approaches. We therefore observe
an association between the concepts of self-monitoring or self-tracking, and empowerment, with
greater patient involvement and better autonomy. Finally, these devices also allow for the
possibility for clinicians to access and review clinical data in real time (9).
Wearables and sleep monitoring
In the field of sleep, the rise of connected devices was largely based on actimetry. The actimeter
uses an accelerometer worn on the wrist and thus detects the movements of the limb (10). Its use
has increased because it is easy to use and allows recordings over periods of time longer than a
single night of polysomnography. However, this assessment method has some limitations. Indeed,
according to the numerous comparative studies with polysomnography, it is shown that the
actimeter hardly detects sleepiness, underestimates the latency of falling asleep, and
overestimates the number of micro-awakenings, compared to the reference examination. Finally,
this device does not provide information on the stages of sleep. Actimetry is therefore limited to
subjects with circadian rhythm disturbances and to evaluation of total sleep time (11). Some
devices use electro-encephalographic and electro-oculographic recordings (12). But these devices,
still little accomplished, require the positioning of several electrodes and are therefore impractical
for home use by the patient (11).
Other devices measure heart rate, and rely on the variability of the heart rate to give the stages of
sleep. Indeed, this variability is higher during paradoxical sleep or nocturnal awakenings, and
lower during slow sleep (13), by sympathetic or parasympathetic action modulations of the
autonomic nervous system (11). These devices are available in different forms: watch, chest band,
electrodes or monitoring on the mattress or pillow, but they still have poor results (10).
Overall, wearables are promising sleep monitoring methods and allow for the recording of several
nights , when polysomnography only assesses a single night of recording (10). Three reviews have
examined the potential features of wearable devices for sleep monitoring (14–16). However, none
of these reviews used a systematic review method in order to report recent clinical research
results. Our hypothesis is that connected devices could reliably and objectively measure sleep
ambulatorily. We therefore conducted a review of the literature regarding the use of connected
devices in sleep assessment.
2.Materials and methods
This literature review aims to identify clinical trials of mobile sleep recording in adult populations
in order to gain an overview of existing assessment techniques and their use in sleep disorders.
The literature search was conducted in June 2018 via the Pubmed, PsycINFO, Science Direct and
Cochrane databases. The key words used were chosen from the terms used in health terminology
of the biomedical reference thesaurus or MeSH terms. The search was conducted using "AND" and
"OR" logistic operators in the MeSH terms, titles, summaries (Figure 1). The keywords used were
« sleep AND wearable electronic devices».
Selection criteria
The primary selection criterion was the reporting of clinical trials using portable devices for sleep
recording in adults. We eliminated studies exploring the recording of activity during the day. Our
review therefore focuses solely on sleep recording. In addition, we selected trials in adult
populations, so pediatric studies were excluded.
Data extraction and analysis
The analysis of the articles was conducted in two stages. As a first step, a census based on the
review of titles and abstracts of scientific papers meeting the inclusion criteria was conducted. In a
second step, the information relating to the publication was extracted (author, date of publication,
country, design of the study, population, number, inclusion criteria, exclusion criteria, scales of
evaluation, objectives of study, protocols, results). The full text of all publications that were not
excluded after analysis of titles and abstracts was reviewed. All studies meeting the inclusion
criteria were included.
2.Results
The steps of the literature review research and analysis are summarized in Figure 1. The initial
search identified 255 articles. No duplicate articles were identified, and screening based on the
titles removed 94 articles. 109 articles were excluded after review of the abstracts. After review of
the full text, 34 additional articles were excluded because they did not meet the inclusion criteria.
Thus, 18 articles meeting the inclusion criteria were included in the final analysis – an overview of
these studies is shown in Table 1.
Studies identified on database
search (n=255 )
Other sources
(n=0)
Records after duplicates removed
(n=255)
Records screened (abstracts)
(n=161)
Record excluded after title
screening (n=94)
Full text addressed for eligibility
(n=52)
Studies included in the review
(n=18)
Full text excluded after abstract
screening (n=109)
Identification Screening Eligibility Included
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Keywords
Studies identified on database
search (n=255 )
Other sources
(n=0)
Records after duplicates removed
(n=255)
Records screened (abstracts)
(n=161)
Record excluded after title
screening (n=94)
Full text addressed for eligibility
(n=52)
Studies included in the review
(n=18)
Full text excluded after abstract
screening (n=109)
Identification Screening Eligibility Included
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Keywords
Figure 1 : PRISMA Flow Chart
Year of publication
Of the 18 studies, 1 (5,56%) study was published in 2008, 1 (5,56%) in 2011, 1 (5,56%) in 2012, 3
(16,67%) were published in 2014, 3 (16,67%) in 2015, 5 (27,78%) studies were published in
2016, 2 (11,11%) in 2017, and 2 (11,11%) in 2018.
Country, origin of development
Of the 18 studies identified, 5 (27,78%) were conducted in the United States, 3 (16,67%) in Italy, 2
(11,11%) were conducted in Israel, 2 (11,11%) in the United Kingdom, 1 (5,56%) study was
conducted in Taiwan, 1 (5,56%) in Thailand, 1 (5,56%) in France, 1 (5,56%) in Korea, 1 (5,56%) in
Australia, and finally 1 (5,56%) study was conducted in Finland.
Studied population
Of the 18 studies, 10 (55,56%) studies were conducted in healthy adults, 4 (22,22%) were
conducted in patients with sleep disorders, 1 (5,56%) with people older than 60, 1 (5,56%) in
patients with fibromyalgia, 1 (5,56%) in patients with bipolar disorder, and 1 (5,56%) in patients
with Parkinson's disease.
Design and size
Of the 18 studies in this review, 10 (55,56%) are comparability studies with the gold standard, 4
(22,22%) are feasibility studies, 3 (16,67%) are population comparison studies, and 1 (5,56%)
assesses the impact of sleep disorders in the clinic. The samples are heterogeneous in size, ranging
from 1 to 15839 patients.
Results analysis
On reviewing the full text of the articles in this review, four categories appeared. Feasibility studies
propose testing new connected tools during sleep, on small samples of subjects. Population
comparison studies compare the sleep of patients to that of healthy subjects. There are also
several studies evaluating connected devices in comparison with polysomnography, a reference
test in sleep assessment. Finally, an article evaluates the impact of sleep disorders in the clinic.
Feasibility studies
In their study, Baron et al (17). aimed to outline the theoretical foundation and iterative process of
designing the "Sleep Bunny", a technology-assisted sleep extension intervention including a
mobile phone app, wearable sleep tracker, and brief telephone coaching. The population was made
of 6 adults with short sleep duration (<7 hours), testing the application with the sleep tracker and
the telephone coaching once a week, over 4 weeks. The survey, based on open-ended questions,
asked participants to provide comments on the content, layout and general feedback about the
app. In conclusion, users enjoyed the wearable sleep tracker and found the app visually pleasing,
but suggested improvements to the notification and reminder features.
The team of Castiglioni et al. (18) studied the feasibility of wearing "MagIC-SCG" sternal wrist
device, during high altitude sleep, which is conducive to hypoxia. Their device recorded the
electrocardiogram, respiratory movements, sternal accelerations, and oxygen saturation. The
study demonstrated the feasibility of recording and using the equipment in high altitude
conditions.
The same device was used by Di Rienzo et al. (19) to study the feasibility of estimating cardiac
functions such as contraction and isovolumic relaxation times, or ventricular ejection time during
sleep. The data were transmitted in real time to an external device via a Bluetooth connection.
According to the authors, this is the first study of its kind, but one that would require more
investigation and more subjects to obtain actionable results.
The team of Kayyali et al. (20), in the United States, investigated the feasibility of portable sleep
recording at the patient's home. Their device, "PSG @ home", was placed in the thoracic region and
recorded respiratory movements, oxygen saturation, airflow, snoring, body position, and the
electrocardiogram. Their study demonstrated the feasibility of using this discreet device overnight
at the subject's home.
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Population comparison
The purpose of the study by Fagherazzi et al. (21) was to highlight the determinants involved in
poor sleep. For this, they calculated the 7-consecutive-night deep sleep/total sleep ratio of a large
number of users of Withings connected devices. They used an algorithm using data provided from
both the accelerometer and temperature sensor. A ratio indicating poor sleep was defined as
below 0,40. Their findings show that young men with elevated heart rate and high blood pressure
were at higher risk for poor sleep quality.
Migliorini et al. (22) compared sleep records between a healthy adult population and a patient
with bipolar disorder. The monitoring was done by the "Smartex" T-shirt equipped with sensors.
The data collected were the electrocardiogram, the respiratory activity and the movements via an
accelerometer, allowing the stages of the sleep and an estimation of the percentage of paradoxical
sleep to be obtained. The results showed a variability of the reduced heart rate in the individual
with bipolar disorder, as well as an increase in the percentage of paradoxical sleep. These results
would need to be confirmed by a larger sample, but seem to be an interesting way of identifying
thymic decompensations.
The study by Sringean et al. (23) compared sleep in the homes of individuals with Parkinson's
disease, with that of their spouses or partners, as healthy controls, to provide a quantitative
analysis of nocturnal hypokinesia. Portable sensors were worn at the trunk and limbs. Records
included number, speed, acceleration, degree and duration of movement / turnarounds, number of
bed exits, and limb movements. They conclude by pointing out the effectiveness of their system to
record nocturnal movements, demonstrating the significant presence of nocturnal hypokinesia.
Comparison with polysomnography
The American team of De Zambotti et al. (24) compared data from the Jawbone UP with
polysomnography data collected simultaneously. The Jawbone UP is a wristband that records
accelerometer data in its first version. Comparisons were made between total sleep time, bedtime,
sleep latency and nighttime awakenings. It has been shown that the estimates of these parameters
are in good agreement with polysomnography, a reference examination in sleep pathologies.
Dafna et al. (25) studied the use of a portable respiratory sound recording tool, with the aim of
estimating respiratory rate by analyzing the audio signal. The data were compared to those of
polysomnography. The authors concluded that their method was reliable and robust in estimating
the respiratory rate, especially since the device is not very intrusive and does not interfere with
the subject's sleep.
Kang et al. (26) compared the accuracy of detecting sleep epochs of the commercial Fitbit Flex
device with polysomnography. They studied a population of 41 individuals with insomnia disorder
and 21 good sleepers. Participants wore the wearable electronic device while undergoing
polysomnography, during 1 night. The measures of interest in this study were Total Sleep Time
(TST), Sleep Efficiency (SE), Sleep Onset Length (SOL), Wake After Sleep Onset (WASO). They
conclude that the frequency of agreement was high in good sleepers but significantly lower in
those with insomnia.
The team of Kuo et al. (27) developed and evaluated a hand-held wrist-based sleep recording tool
based on actimetry. The developed device was judged to be energy efficient and highly accurate in
measuring sleep efficiency, total sleep time, sleep time, and nighttime awakenings.
Polysomnography measurements were taken simultaneously. It was shown that the different
variables were concordant, and significantly so for total sleep time and sleep efficiency. According
to the authors, this system is interesting for obtaining objective sleep data at the patient’s home.
In their pilot study, Looney et al. (28) compare electroencephalographic recordings recorded by
standard electrodes at the level of the scalp, and by an intra-auricular device, simultaneously
during sleep. The lines were read blindly by an expert. The results showed a significant
concordance of the two recordings.
Mantua et al. (29) compared the data from five portable connected devices recording sleep with
those of the gold standard, polysomnography. The devices under study were Actiwatch, Basis,
Misfit Shine, Fitbit Flex, and Withing Pulse O2. The recordings were made simultaneously at the
participant's home, with participants wearing the five devices on the wrists, and
polysomnography was installed. Significant data loss was reported by "Fitbit Flex" and "Misfit
Shine". The correlation analysis allows them to conclude that there is no significant difference in
estimating total sleep time between polysomnography and each of the five devices. In addition,
only "Actiwatch" had concordant data with the baseline sleep efficiency test. The light sleep time
differed for all devices. Finally, a correlation of deep sleep time was significant only for "Basis".
The team of Parak et al. (30) compared the nightly heart rate recording of the connected watch
"PulseOn" with the reference test, the electrocardiogram. The study, conducted at home, shows
that the device correctly detects 99.57% of heartbeats, making it an accurate method during sleep.
In their sleep laboratory study, Rodriguez-Villegas et al. (12) compared the effectiveness of a
wireless system in the detection of apnea and hypopnea with that of polysomnography. The 17-
gram apparatus was placed on the skin of the anterior aspect of the neck. It recorded turbulence in
the trachea using an acoustic chamber. Data were analyzed blind. The tolerance of the device was
greater than that of polysomnography. However, the results did not agree with the gold standard
regarding the correct detection of hypopneas. In conclusion, this tool could be an adequate
solution for the monitoring of apneas in ecological conditions, but would not replace a complete
recording in the sleep laboratory.
Sano et al. (31) studied the comparison of electroencephalogram data with the Q Sensor Affectiva,
concerning the detection of waking and sleeping phases in a specialized hospital laboratory. The Q
Sensor Affectiva is a watch that records skin temperature, cutaneous conductance and
acceleration. In their conclusion, it appears that the combination of acceleration and skin
temperature is most effective in the sleep / wake classification.
The Australian team of Sargent et al. (32) evaluated the validity of a commercial wearable device,
the Fitbit HR Charge, for measuring Total Sleep Time (TST). To do this, they compared the
commercial wearable device with the gold standard, the polysomnography, during 30 nights and
20 naps. They chose a population of 12 well-trained young athletes. This study showed that the
Fitbit HR Charge overestimated TST for night-time sleep periods and for daytime naps.
Impact of sleep in the clinic
In the study by Agmon et al. (33), the impact of sleep on walking performance in institutionalized
elderly was measured using a connected watch using an accelerometer. Sleep efficiency, sleep
latency, total sleep time, and nocturnal awakenings were taken into consideration. The team
demonstrated that a decrease in recovery sleep was significantly associated with a decrease in
start-up speed and a greater variability of walking during double tasks.
4.Discussion
This review of the literature shows an increasing interest in the use of connected health devices
for sleep assessment. Their use is proposed in a broad spectrum of pathologies as well as in
healthy individuals.
Relyability
First of all, this review and other recent studies (34–37) indicate that health scientists no longer
consider wearables as “toys”. Nowadays, they are tools to help patients, doctors and scientists.
Thanks to new technologies, on the one hand we are now able to wear small and non-intrusive
devices during daily and nightly life (38) and on the other hand we are also capable to deeply
analyse big datasets (39). In other words, wearables and systems to collect and analyse
physiological sleep data are now acceptable and powerful. Even if this new perspective is
promising, it is only the beginning as previous studies often included only small samples. In this
review of the literature, only 7 studies among 18 included 30 participants or more. One could
expect this will improve thanks to the increase of the acceptance (40,41). Recent findings also
emphasize that little is still known about physiological monitoring in ecological situations (42).
This could be explained because we could not easily record wide datasets before. The most
common methodology identified in this review was motion sensing via accelerometry, a well-
studied method in the field of sleep research which has been used for decades (43). The research
literature consistently shows that wrist accelerometry, even in healthy adults, has high sensitivity
for sleep, while having much lower specificity for sleep.
Another interesting finding among the four feasibility studies identified in this review is that
outpatients did not only experience worn wrists devices but also slept with electrodes and
cutaneous sensors. Despite of this, conclusions still pointed out the high feasibility level of studies
with such an equipment. Even if these studies should be proceeded with larger samples, one could
guess that on-board polysomnography-tools are on the way.
Limitations of the review’s method
Although the studies selected in this review are recent, the rapid evolution of technologies in this
area makes it difficult to adjust research to keep pace with commercial releases. Since starting the
review process, additional articles may have been published. Moreover, while the conclusions are
encouraging, most of them are pilot studies with small samples. In addition, the tools tested are
commercial, and therefore have no health device label. Limits on scientific validity mean that these
devices are not usable in a current clinic, and it may be premature to recommend them. Given the
rapid progression of technologies, it does not seem unrealistic to think that more complete and
validated devices will be available soon. Moreover, the heterogeneity of the population studied in
this review makes it difficult to issue a general conclusion. In return, this reflects the broad
spectrum of usability of connected devices in the field of sleep. Finally, it should be noted that this
review of the literature does not provide any data on the use of these objects in the long term,
because they are mostly short clinical trials, with devices that may have defects in the collection of
data due to limited battery for example.
One of the most significant issue related to wearables use in clinical monitoring is to establish the
congruency between the well-proven gold standard and the new emerging wearables. Indeed, the
results from polysomnography comparisons revealed that sleep experts validated the data from
the mobile devices. Since these experts have experience working with polysomnography, it
reinforces the statement. From a methodological point of view, the study from Looney et al (25)
highlighted the importance of a blind interpretation process. By this respect, one could suggest
that if the same expert could work indifferently with both system, wearables definitely are
efficient. However, further studies with more participants is required to generalize these results,
this review demonstrates the potential for wearables to get generate more knowledge about sleep.
Ethical aspects
The expansion of connected devices has raised ethical concerns. On the one hand, there is a risk of
instrumentalisation of the human body and health. The purely technical reading of a physical or
somatic disorder is a reduction of a more complex reality. Quantification of the self would lead to a
reduction of social representations of illness and health in general: numerical data, compared to a
norm, could impoverish the variety of feelings and the expression of the patient's experience, as
well as the clinic associated with it. In addition, the lack of contextualization engendered could
devalue the knowledge of practitioners who value the experience. On the other hand, there are
questions about reliability and data protection. Patients may be apprehensive about the risk of
loss of control over data and privacy. It is therefore essential to establish a climate of trust around
the use of these tools in medical practice. Finally, connected devices are also sometimes presented
as a threat to social solidarity, on which the French health system is based. We are talking about a
"digital divide", and the "unconnected" or those whose psychological state would not benefit from
these tools, could then be victims of social, cultural and economic marginalization.
Moreover, it has been shown that individuals lose interest in connected objects after a few months
of use. The reasons given are a lack of adaptation to the subject's needs, or adjustment of use
through the developmental process.
Weakness of analysis system
This review did not identify any studies describing the use of data mining techniques. Data mining
is a set of techniques that can be used to explore clinical questions in large databases. The data
mining process includes several steps, including data selection, data processing, and machine
learning to identify which factors may influence results. For example, data mining techniques have
been described to find relationships and patterns between electronic data and neurobiological
data (44). Machine learning techniques allow processing of real-time observational information by
continuously learning from data to build understanding and uncover previously unexpected
associations and patterns in data (45). Commercial wearables devices implicitly use these
techniques, at least during development process of the product. These techniques may help
clinicians to better interpret recordings provided by wearables. Unsupervised machine learning is
the machine learning task of inferring a function to describe hidden structure from "unlabeled"
data . These techniques should be also described in making sense of enormous wearables datasets
is a common challenge in the Big Data era that is best overcome using data mining techniques.
The current landscape of marketing claims that stretch beyond the scant validation literature may
contribute to the discrepancy between consumer and health care community adoption of sleep
monitoring devices. Clinicians and researchers, more familiar with the extensive experience
polysomnography (PSG) and actigraphy, still seem to be reluctant to integrate wearables into
clinical practice, pending rigorous validation. Wellness claims are not necessarily adapted to
clinical practice setting, and as a result, has delayed the adoption of this devices in clinical practice.
In this review, we described several clinical applications of consumer sleep monitoring technology.
Consumer sleep devices contribute to the blurry boundary between sleep as a medical concept
and sleep as “wellness” and the need for a framework to interpret consumer sleep device outputs.
Future applications
Wearables are able to perform passive (or autonomous) data gathering, i.e., to extract information
about the users without their intervention. Actigraphy, geolocation, and communication activity
are usual features of current smartphones and may be useful indicators, if properly processed, of
the individual’s condition or state (46). Advances in sensor technologies, and novel textile-
electronic integration technics also draw new perspectives for behavioral ecological assessment
(BEA). Moreover, it is currently possible to find commercially available wearable sensing
technologies for several wellness and clinical purposes, ranging from simple heart rate monitors
(HR) (47) to monitors of physical activity, rehabilitation after surgical intervention or sleep quality
assessment. Overall, an extensive panel of physical and mental conditions (e.g., insomnia, elderly,
diabetic, cardiac, or respiratory problems) can be remotely monitored by the appropriate health
care professional (e.g., physician, doctor, nurses). These devices are often bound to a smartphone,
increasing the networking capabilities and the user experience. Collected data can be processed
and transferred over the Internet to a remote clinical back-end server for further analysis,
assessment, and decision making and intervention.
Conclusion
This review of the literature on connected devices in health shows the growing interest for these
new technologies, as well as the wide applications that can be made of them. Indeed, it is observed
that the studies can reflect different specialties of medicine and that the populations studied are
varied. In addition, this interest is recent, the vast majority of studies dating from 2014.
Qualitatively, the majority of devices are considered comfortable (30), easy to use (20), and
preserve the natural sleep of the user (25,28), making them good candidates for home care
(12,22,27). In addition, they have an economic advantage and the preliminary results of this study
show a good correlation with the reference examination (24). Given the many benefits, we must
consider connected devices as promising tools for the modernization of care.
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