An Evaluation of a Non-contact Biomotion Sensor with Actimetry

Abstract

Actimetry is a widely accepted technology for the diagnosis and monitoring of sleep disorders such as insomnia, circadian sleep/wake disturbance, and periodic leg movement. In this study we investigate a very sensitive non-contact biomotion sensor to measure actimetry and compare its performance to wrist-actimetry. A data corpus consisting of twenty subjects (ten normals, ten with sleep disorders) was collected in the unconstrained home environment with simultaneous non-contact sensor and ActiWatch actimetry recordings. The aggregated length of the data is 151 hours. The non-contact sensor signal was mapped to actimetry using 30 second epochs and the level of agreement with the ActiWatch actimetry determined. Across all twenty subjects, the sensitivity and specificity was 79% and 75% respectively. In addition, it was shown that the non-contact sensor can also measure breathing and breathing modulations. The results of this study indicate that the non-contact sensor may be a highly convenient alternative to wrist-actimetry as a diagnosis and screening tool for sleep studies. Furthermore, as the non-contact sensor measures breathing modulations, it can additionally be used to screen for respiratory disturbances in sleep caused by sleep apnea and COPD.

Somnography using unobtrusive motion sensors and Android-based mobile phones

“…This is comparable to the results of [9], where a sensitivity and specificity of 79% and 75% were obtained analyzing 20 subjects. However, a direct comparison to previous work is difficult.…”

“…The two resulting signals had different response characteristics to different periods of movement activity. Digital integration was chosen as it is better suited for movement identification than zero crossing methods or time above threshold [9].…”

“…To avoid the drawbacks of PSG many attempts have been made to find alternate methods for sleep analysis outside the sleep laboratories [7], [8], [9]. In 2007, Choi et al assessed the feasibility of unobtrusive actigraphy using load-sensing cells integrated into the bed posts [8].…”

“…They showed that sleep/wake assessment can be done only by analyzing body movements. Also in 2007, Fox et al compared a reference actimeter to their recording method using a Doppler radar positioned about one meter away from the subject's bed [9].…”

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“…The body movement index is calculated as follows: two separate integration operations are applied to the axis-independent signal over a two second (I 2 ) and four second (I 4 ) window (the signals I 2 and I 4 have different response characteristics to different periods of movement activity). Digital integration was chosen as it is more suitable for identifying movement, compared to other methods such as zero crossing or time above threshold [35]. The body movement index is then calculated as the summation of the series of I 2 and I 4 values starting from the 4th second till the 30th second, in a step size of 2 seconds.…”