Sleep Posture Affects Sleep Parameters Differently in Young and Senior Japanese as Assessed by Actigraphy

Author(s) :Akiko Nojiri, Chikako Okumura, Yushi Ito

ABSTRACT

Objective sleep parameters
Objective sleep parameters (total minutes scored as awake (TMSA), total sleep time (TST), wake after sleep onset (WASO), sleep efficiency (SE), sleep onset latency (SOL), activity mean score (AMS), activity index (ACTX), sleep fragmentation index (SFX), wake episode (WEP) and long wake episodes (LWEP)) assessed by actigraphy in younger and senior groups.

In an attempt to study the relationship between sleep postures and sleep parameters assessed by actigraphy, we applied the newly developed Activity Monitoring and Evaluation System (A-MES) and actigraphy at the same time to younger and senior Japanese volunteer groups. It was found that sleep postures and diurnal activity determines, to some extent, sleep parameters including activity mean score (AMS), activity index (ACTX), waking episodes (WEP) and sleep fragmentation index (SFX). It was also found that sleep properties are different in younger and senior Japanese.

For example, increase in the proportion of time in the supine position resulted in enhancement and deterioration of the sleep in the younger and senior groups, respectively. Furthermore, there were correlations between supine posture and AMS, ACTX, SFX, total minutes scored as awake (TMSA) and WEP obtained by actigraphy in the younger group, but only AMS and ACTX in senior group. In addition, we also assessed sleep parameters by use of questionnaires, and found that objective sleep quality was rather poor but subjective sleep quality was better in the senior group. In the younger group, in contrast, objective sleep quality was better but subjective sleep quality was poor. On the other hand, there was no correlation between sleep parameters assessed by actigraphy and self-report at all. The present study with A-MES and actigraphy provides the first evidence that sleep posture affects sleep quality and is a convenient, inexpensive and home-based method for studying sleep.

Introduction
Sleep evaluation in humans has been performed with polysomnography (PSG), a technique considered the “gold standard” for sleep studies. However, subjects have to stay in the sleep laboratory for at least four nights with many electrodes and sensors. As an alternative to PSG, the use of wrist actigraphy (activity-based monitoring), an instrument that measures wrist motor activity to provide an indirect assessment of sleep through the use of algorithm, has become an essential tool in sleep research and sleep medicine [1

] [2] . However, it is not feasible to assess sleep postures per se by use of actigraphy, and till now little study has been carried out on the relation between sleep postures and sleep parameters assessed by actigraphy.

It was first noticed, from the analysis of the sleep characteristics and sleep positions of good and poor sleepers [3] [4] , assessed with a Super 8 Camera taking one frame every 8 seconds providing 3600 frames over 8 hours, that sleep positions constitute an important sleep parameter that may be related to the sleep quality.

In a previous study, by use of a newly developed Activity Monitoring and Evaluation System (hereafter referred as A-MES) [5] [6] , we observed postures, posture shifts, duration of postural immobility and frequency of body movements during the time in bed of four Japanese age groups [7] . The reliability made by A-MES on postures and movements was examined by the comparison with those obtained by video-recording the behavior of subjects, and the results obtained with A-MES yielded good agreement with those obtained by analysis of videotape recordings [8] . The subjects slept two or three consecutive nights at home wearing night clothes with two A-MES attached to trunk and left thigh. This method allows natural and undisturbed sleep in the subject’s own bed and gives reliable data through one to two nights recording. We found that there is significant ontogenetic decrease in supine position, and corresponding increase in sleep posture lying on the right, although there was no difference in the number of posture shifts or the duration and frequency of the postural immobility across the four age groups. A-MES provides a convenient, inexpensive and home-based method for studying putative sleep movement. However, a limitation of this method was that it was not possible to distinguish awake and sleep states [7] . Therefore in the present study, we applied actigraphy and A-MES at the same time to younger and senior Japanese subjects in an attempt to study the relationship between sleep postures and sleep parameters. In addition, to assess the subjective sleep quality, we used Pittsburg Sleep Quality index [9] and Oguri-Shira- kawa-Azumi Sleep Inventory MA version [10] (hereafter referred as PSQI and OSA-SI-MA, respectively).

Thus, the aim of the present study was threefold. Firstly we performed a comparative study on sleep postures and activities during 24 hours in younger and senior Japanese groups by use of A-MES and actigraphy at the same time. Secondly, we studied the relationship between sleep posture and diurnal activities with the sleep parameters obtained by actigraphy. Finally, we studied the relationship, if any, between subjective and objective sleep quality.

Conclusion
By application of newly developed A-MES and actigraphy to younger and senior Japanese volunteer groups at the same time, we obtained following conclusions. Firstly, sleep postures and diurnal activity determine, to some extent, sleep parameters including AMS, ACTX, WEP and SFX assessed by actigraphy, and this is the first evidence that sleep posture affects sleep quality. Secondly, sleep properties are different in younger and senior Japanese, including the relationship between the proportion of time in the supine position and sleep quality, or AMS, ACTX, SFX, and TMSA. Thirdly, we also assessed sleep parameters by use of questionnaires; however there was no correlation between sleep parameters assessed by actigraphy and self-report at all. Finally, present study with A-MES and actigraphy provides a convenient, inexpensive and home-based method for studying sleep.

Source:

Journal: Health


DOI: 10.4236/health.2014.621332 (PDF)
Paper Id: 52550 (metadata)

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