Comparisons of Portable Sleep Monitors of Different Modalities: Potential as Naturalistic Sleep Recorders

Abstract

Background: Humans spend more than one-fourth of their life sleeping, and sleep quality has been significantly linked to health. However, the objective examination of ambulatory sleep quality remains a challenge, since sleep is a state of unconsciousness, which limits the reliability of self-reports. Therefore, a non-invasive, continuous, and objective method for the recording and analysis of naturalistic sleep is required.

Objective: Portable sleep recording devices provide a suitable solution for the ambulatory analysis of sleep quality. In this study, the performance of two activity-based sleep monitors (Actiwatch and MTN-210) and a single-channel electroencephalography (EEG)-based sleep monitor (SleepScope) were compared in order to examine their reliability for the assessment of sleep quality.

Methods: Twenty healthy adults were recruited for this study. First, data from daily activity recorded by Actiwatch and MTN-210 were compared to determine whether MTN-210, a more affordable device, could yield data similar to Actiwatch, the de facto standard. In addition, sleep detection ability was examined using data obtained by polysomnography as reference. One simple analysis included comparing the sleep/wake detection ability of Actiwatch, MTN-210, and SleepScope. Furthermore, the fidelity of sleep stage determination was examined using SleepScope in finer time resolution.

Results: The results indicate that MTN-210 demonstrates an activity pattern comparable to that of Actiwatch, although their sensitivity preferences were not identical. Moreover, MTN-210 provides assessment of sleep duration comparable to that of the wrist-worn Actiwatch when MTN-210 was attached to the body. SleepScope featured superior overall sleep detection performance among the three methods tested. Furthermore, SleepScope was able to provide information regarding sleep architecture, although systemic bias was found.

Conclusion: The present results suggest that single-channel EEG-based sleep monitors are the superior option for the examination of naturalistic sleep. The current results pave a possible future use for reliable portable sleep assessment methods in an ambulatory rather than a laboratory setting.

Keywords: activity recorders; polysomnography; portable sleep monitors; single channel EEG; sleep estimation.

Figure 1

Representative actigraphs from Actiwatch, MTN-210 on the wrist, MTN-210 on the body, and corresponding analysis. Actigraphs of 7 days prior to and during PSG are shown, where the days and time when PSG was conducted are shown on the X-axis, and the activity counts for every 2 min (A–C) are shown on the Y-axis. Correlation of the activity between MTN-W and Actiwatch is compared by scatter plot (D) or MTN-B and MTN-W (E). MTN-B, MTN-210 on the body; MTN-W, MTN-210 on the wrist; PSG, polysomnography.

Figure 2

Sensitivity preferences and differences between MTN-W and Actiwatch. Distributions are shown by frequency on the Y-axis, and corresponding activity strength is shown on the X-axis (A,B). Sensitivity preferences were compared. The shaker speed is indicated on the X-axis, and the corresponding counts are displayed on the Y-axis (C). MTN-W, MTN-210 on the wrist.

Figure 3

Sleep parameters were compared among the devices/conditions. Sleep duration (A), sleep latency (B) and wake after sleep onset (C) estimations by all the devices/conditions are compared. Conditions are displayed on the X-axis, and parameter values on the Y-axis. White box shows data from PSG as a reference. Asterisks show levels of significance: *P < 0.05, **P < 0.01, ***P < 0.001. PSG, polysomnography.

Figure 4

Bland–Altman plot analysis of sleep duration estimations. Bland–Altman plot for sleep duration estimations by all the methods. Horizontal solid lines represent the means of the differences, and dashed lines represent 95% limits of agreement.

Figure 5

Comparisons of epochs ratio, correctly assigned to sleep or awake. Bar plots represent percentage of epochs correctly assigned to either sleep or awake are shown. Sleep/wake detection made by portable devices are examined in each PSG-defined sleep stages. In awake, % of epochs correctly detected by portable devices as awake are shown. In other sleep stages, % of epochs correctly detected by portable devices as sleep are shown.