Elsevier

Sleep Medicine

Volume 4, Issue 3, May 2003, Pages 177-184
Sleep Medicine

Fast Track article
Preliminary observations on the effects of sleep time in a sleep restriction paradigm

https://doi.org/10.1016/S1389-9457(03)00061-3Get rights and content

Abstract

Objective: To evaluate of the effect of 7 days of sleep restriction – with sleep placed at the beginning of night or early morning hours – on sleep variables, maintenance of wakefulness test, and serum leptin.

Methods: After screening young adults with questionnaires and actigraphy for 1 week, eight young adult males were recruited to participate in a sleep restriction study. The subjects were studied for baseline data for 2.5 days, with 8.5 h per night in bed, and then over 7 days of sleep restriction to 4 h per night with a 22:30 h bedtime for half the group and a 02:15 h bedtime for the other half. At the end of study, after one night of ad libitum sleep, subjects again had 2 days of 8.5 h in bed. Wakefulness was continuously verified and tests, including Maintenance of Wakefulness (MWT), were performed during the scheduled wake time. Blood was drawn six times throughout the 24 h of the 7th day of sleep restriction and after 2 days of the post-restriction schedule.

Results: There was individual variability in response to sleep restriction, but independent of group distribution, MWT was significantly affected by sleep restriction, with the early morning sleep group having less decrease in MWT score. Sleep efficiency was also better in this group, which also had shorter sleep latency. Independent of group distribution there was a greater increase in the percentage of slow wave sleep than rapid eye movement sleep, despite a clear internal variability and variability between subjects. Peak serum leptin was significantly decreased with 7 days of sleep restriction for all subjects.

Conclusion: Sleep restriction to 4 h affected all subjects, but there were individual and group differences in MWT and sleep data. In this group of young adult males (mean age 19 years), there was a better overall adaptation to the early morning sleep, perhaps related to the general tendency in most adolescents to present some phase-delay during late teen-aged years.

Introduction

Sleep restriction is common in the lives of many people. Different surveys have shown that, from school-aged children to professionals, people restrict their total sleep time to perform chores and/or engage in social, professional or familial activities. A cumulative reduction in the normal nightly sleep period results in decrements in daytime function and quality of life [1].

There is a range of responses to experimentally reduced total sleep time. Powell et al. [2], using a road circuit with signal lights, road construction and a single-lane segment, studied the effect of 7 days of sleep restriction to 4 h per night on driving performance. Subjects were also evaluated on their ability to avoid a ball rolled in front of the car and to slalom between cones. The results were variable, from very significant decrements in performance to the point of a complete inability to drive, to no change compared to baseline. Philip et al. [3], who had the same subjects drive 600 miles on a highway before and immediately after one night of sleep deprivation, had similar findings. There are individual differences in the impact of sleep restriction/deprivation on driving performance.

Many factors may contribute to these differences. Our protocol was aimed at addressing the following question: Does the time of sleep during the night in a sleep restriction paradigm impact the next day's behavior? As our protocol was complex, we will only present a subset of findings on the effect of sleep restriction to 4 h per night for 7 days on nocturnal sleep architecture, Maintenance of Wakefulness test (MWT) [4], breathing during sleep and serum leptin levels compared to baseline [5], [6], [7], [8]. The presentation will more specifically address the following questions: Does the placement of sleep lead to different changes in the percentage of slow wave sleep and rapid eye movement (REM) sleep during the restriction period? Our hypothesis was that it would. Do the expected changes in MWT scores relate to the placement of the nocturnal sleep? Our hypothesis was that it would not, with sleep restriction being the leading factor in the MWT findings. Does sleep restriction lead to the appearance of snoring? Our hypothesis was that it would not in these normal young individuals with normal weight and cranio-facial anatomy. Would the sleep restriction have an impact on the serum leptin level? Our hypothesis was that it would, with an increase in serum leptin associated with an increase in food intake.

Section snippets

Protocol

Young male adults from a university were recruited by word of mouth and from advertisements to participate in a 12-day experiment during the summer. Payments to the subjects were based on the number of days of participation, with a maximum of $1000 for completing the study. All subjects had a normal physical evaluation at entry, including a urine test for medication and drug intake. They had overall sleep times within a normal range, and Epworth Sleepiness [9] and Horne and Osberg questionnaire

Results

All subjects completed the protocol. No mood changes occurred during the experiment, as was indicated by a daily visit by a psychiatrist as mandated by the Institutional Review Board (IRB). Of the eight young men, seven were between 18 and 20 years of age and in vacation between high school and college, and the other was 25 years old, out of college and temporarily unemployed. Subjects were randomized to Groups A and B at entry. All of the subjects had normal clinical evaluation, including a

Discussion

Sleep restriction is common in the general population. It may be caused by external conditions or self-inflicted, and varies in degree.

Our experiment on young male subjects produced several findings, some unexpected; many of our ‘a priori’ hypotheses were not confirmed. We hypothesized that the group assigned to bed at 02:30 h would have more REM sleep than the group which slept earlier in the night. This hypothesis was not clearly supported in this preliminary study. Overall, there was always

Acknowledgements

This work was supported by the Sleep Education and Research Foundation of Palo Alto.

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