Sleep disruption and sleep position: Increased wake frequency in supine predicts lateral position preference

Abstract

Little is known about the physiological and biomechanical factors that determine individual preferences in lying posture during sleep. This study investigated relationships between position preference and position-specific arousals, awakenings, limb movements and limb movement arousals to explore the mechanisms by which biomechanical factors influence position preference. Forty-one mature-aged adults underwent 2 nights of at-home polysomnography ~2 weeks apart, on a standardised firm foam mattress, measuring nocturnal sleep architecture and position. The lateral supine ratio and restlessness indices specific to lateral and supine positions including limb movement index, limb movement arousal index, arousal index, wake index, respiratory arousal index and apnea-hypopnea index were calculated and analysed via linear mixed-effects regression. In the supine position, all restlessness indices were significantly increased compared with the lateral position, including a 379% increase in respiratory arousals (β = 7.0, p < 0.001), 108% increase in arousal index (β = 10.3, p < 0.001) and 107% increase in wake index (β = 2.5, p < 0.001). Wake index in the supine position increased significantly with more lateral sleep (β = 1.9, p = 0.0013), and significant correlation between lateral supine ratio polysomnography 1 and lateral supine ratio polysomnography 2 (β = 0.95, p < 0.001) indicated strong consistency in sleep preference. Overall, the findings suggest that some individuals have low tolerance to supine posture, represented by a comparatively high wake index in the supine position, and that these individuals compensate by sleeping a greater proportion in the lateral position.

Keywords: arousals; awakenings; lateral position; positional therapy; sleep; sleep apnea; sleep position; sleep posture; supine position.

FIGURE 1

Level 2 ambulatory polysomnography (PSG) set‐up with Nox A1s.

FIGURE 2

Relationship between first and second polysomnography (PSG) lateral supine ratio (LSR). (a) Scatter plot of LSR on the 1st night of PSG (LSR PSG1) on the x‐axis, and LSR PSG2 on the y‐axis. The solid line shows the linear regression model (β = 0.95, p < 0.001). (b) Scatter plot of the difference in LSR between PSG1 and 2 on the y‐axis, and the days between PSG1 and 2 on the x‐axis.

FIGURE 3

Differences in the relationship with lateral supine ratio (LSR) between wake index in the supine position (WI‐S) and wake index in the lateral position (WI‐L). Shown are scatter plots demonstrating the relationship between LSR and WI‐S (a) and WI‐L (b), where the black solid line shows the mean positional WI, and red dotted lines show standard deviations. The black dashed line shows the linear mixed‐effects regression model described by intercept and coefficient (β). Histograms are shown that demonstrate the difference in distribution of WI‐S (c) and WI‐L (d). It can be seen that the plurality of participants have WI‐L or WI‐S within 1.5–2.5 awakenings per hour; however, WI‐S is more distributed with wider standard deviations.

FIGURE 4

Participant 82 polysomnography (PSG)1 and PSG2 sleep event timelines. PSG1 timeline is shown on the left, and PSG2 on the right. Dotted vertical lines represent sleep onset and sleep offset. The top hypnogram shows continuous sleep event data, including sleep posture (supine in green, left in cyan, right in red, prone in blue), limb movement arousal (LMA), limb movement (LM), arousal and sleep stages, including wake, rapid eye movement (REM), N1, N2 and N3. Histograms are shown representing the count of wakes, arousals, LM and LMA within 20‐min epochs starting from the hour. The bottom table shows sleep statistics relating to each night of sleep for the participant, total sleep time (TST) is expressed as hh:mm, % N3, N2, N1 and REM calculated as proportion of TST.

FIGURE 5

Participant 61 polysomnography (PSG)1 and PSG2 sleep event timelines. Similar layout to Figure 4.