Past, Present, and Future of Multisensory Wearable Technology to Monitor Sleep and Circadian Rhythms

Abstract

Movement-based sleep-wake detection devices (i.e., actigraphy devices) were first developed in the early 1970s and have repeatedly been validated against polysomnography, which is considered the “gold-standard” of sleep measurement. Indeed, they have become important tools for objectively inferring sleep in free-living conditions. Standard actigraphy devices are rooted in accelerometry to measure movement and make predictions, via scoring algorithms, as to whether the wearer is in a state of wakefulness or sleep. Two important developments have become incorporated in newer devices. First, additional sensors, including measures of heart rate and heart rate variability and higher resolution movement sensing through triaxial accelerometers, have been introduced to improve upon traditional, movement-based scoring algorithms. Second, these devices have transcended scientific utility and are now being manufactured and distributed to the general public. This review will provide an overview of: (1) the history of actigraphic sleep measurement, (2) the physiological underpinnings of heart rate and heart rate variability measurement in wearables, (3) the refinement and validation of both standard actigraphy and newer, multisensory devices for real-world sleep-wake detection, (4) the practical applications of actigraphy, (5) important limitations of actigraphic measurement, and lastly (6) future directions within the field.

Performance of a Multisensor Smart Ring to Evaluate Sleep: In-Lab and Home-Based Evaluation Relative to Polysomnography and Actigraphy: Importance of Generalized Versus Personalized Scoring

“…For this reason, peripherally scored sleep staging data are still insufficient for replacing sleep stages derived from polysomnography. Regardless, values from at-home sleep tracking devices can be useful, especially as they can be sampled over many days and in large numbers of people, unlike polysomnography 9,11 . For sleep stage classification, the performance of the Happy Generalized model performed about the same as other similar devices on the market both in-lab and at-home.…”

“…Further, the concept of evaluating the performance of devices relative to their context has emerged as a strategy for addressing the limitations of more traditional validation approaches 10,36 . With the establishment of these standards, applications of novel sensors and scoring strategies have been called for 11 .…”

“…Personal sleep health is increasingly recognized as an important factor in physical and mental health, affecting one’s performance, response to stressors, and emotional regulation throughout the day 1–6 . Wearable technology provides opportunities to assess sleep health in real-world situations so that associations with relevant health and performance outcomes can be examined in the context of reliable, objective recordings in naturalistic settings 7–11 . This has proven useful, as wearable technology to assess sleep has been used to explore associations with cardiovascular disease 12,13 , metabolic dysregulation 12,14 , inflammation 15,16 , mental health 17,18 , physical performance 19 , and other outcomes, including mortality 20 .…”

Technical, Regulatory, Economic, and Trust Issues Preventing Successful Integration of Sensors into the Mainstream Consumer Wearables Market

“…In direct comparison against PSG, multi-sensor wearables using PPG fall short when determining sleep stages or identifying periods of wake during a sleep episode [ 10 , 14 ]. Multi-sensor sleep trackers still represent a step forward, but are not accurate enough to be considered replacements for laboratory measurements [ 10 , 15 ]. This is just one example of how laboratory sensors and consumer wearables may differ with regard to measuring signals of interest.…”

Development of a non-contact sleep monitoring system for children

“…There are various sleep measurement devices, and methods based on body movements ( 17 ). Two commonly used devices include the smartwatch and smartphone.…”