Table 1.
Visually scored sleep variables
| Age groups (n = 51) | 2–5 years (n = 8) | 5–8 years (n = 5) | 8–11 years (n = 12) | 11–14 years (n = 9) | 14–17 years (n = 12) | 17–20 years (n = 5) |
|---|---|---|---|---|---|---|
| Sleep variables | ||||||
| Time in bed (min) | 651.6 ± 18.4 | 579.9 ± 17.4 | 528.0 ± 9.9 | 523.6 ± 13.4 | 469.6 ± 13.8 | 399.6 ± 24.8 |
| Total sleep time (min) | 581.9 ± 10.1 | 520.6 ± 16.7 | 444.5 ± 12.3 | 469.5 ± 17.1 | 429.2 ± 17.7 | 363.5 ± 15.1 |
| Sleep efficiency (%) | 89.6 ± 2.0 | 89.8 ± 1.5 | 84.4 ± 2.7 | 89.7 ± 2.4 | 91.1 ± 1.8 | 91.4 ± 2.1 |
| Sleep latency (min) | 24.8 ± 7.3 | 18.5 ± 4.3 | 24.8 ± 2.5 | 22.7 ± 5.4 | 20.6 ± 3.6 | 13.6 ± 3.2 |
| Waking after sleep onset (min) | 46.5 ± 14.2 | 43.0 ± 9.9 | 62.1 ± 13.8 | 35.4 ± 8.6 | 23.5 ± 5.0 | 25.7 ± 9.0 |
| Stage 1 (%) | 4.2 ± 0.3 | 3.5 ± 0.8 | 7.3 ± 0.9 | 7.5 ± 1.0 | 8.6 ± 1.3 | 5.4 ± 1.6 |
| Stage 2 (%) | 47.8 ± 2.2 | 51.7 ± 2.2 | 46.5 ± 2.4 | 46.4 ± 2.4 | 52.4 ± 1.3 | 57.6 ± 2.1 |
| SWS (%) | 20.4 ± 1.2 | 20.0 ± 1.0 | 27.3 ± 2.9 | 26.4 ± 2.2 | 20.7 ± 1.3 | 17.8 ± 3.4 |
| REM sleep (%) | 27.6 ± 1.3a | 24.8 ± 1.1 | 18.8 ± 1.2b | 19.7 ± 1.1b | 18.3 ± 1.4b | 19.2 ± 1.4b |
| Sleep cycle duration (min) | 89.8 ± 3.4 | 87.0 ± 3.0 | 94.2 ± 5.3 | 92.7 ± 3.9 | 96.6 ± 3.5 | 95.4 ± 3.4 |
Sleep variables (mean ± SE) of all subjects with at least 4.5 h of recorded sleep time and four sleep cycles subdivided into age groups (2.4–19.4 years, n = 51). Sleep efficiency, Total sleep time expressed as a percentage of time in bed; Sleep latency, latency to the first occurrence of stage 2 sleep; Waking after sleep onset, expressed in minutes; sleep stages are expressed as a percentage of total sleep time; SWS, slow-wave sleep as stage 3 sleep; REM sleep, rapid eye movement sleep. Sleep cycle duration, includes only the first four sleep cycles. Because subjects were awoken in the morning, the last sleep cycle could not always be completed. Thus, we applied two additional criteria for the analysis of cycle duration: in subjects with only four cycles but with a missing REM sleep episode in the last cycle, the last cycle was excluded from the comparison (n = 6). Moreover, only sleep cycles containing a minimum of 75 epochs of NREM sleep were included. Sleep variables Time in bed and Total sleep time were excluded from group comparisons because sleep was restricted in the morning (for details, see Materials and Methods). A one-way ANOVA with factor age group was significant for stage 1 and stage 2 sleep, SWS, and REM sleep (all p < 0.05, F = 0.6–7.7, df = 5). Post hoc Scheffé tests revealed a significant group difference for REM sleep as indicated by letters (a,bp < 0.05). Age groups with different letters differ significantly from each other.