Timing of Sleep in the Break Between Two Consecutive Night-Shifts: The Effect of Different Strategies on Daytime Sleep and Night-Time Neurobehavioural Function

Figures & data

Figure 1 Study protocol. Black horizontal bars represent sleep opportunities; grey horizontal bars represent simulated 12-hour night-shifts; and black circles represent assessments of neurobehavioural performance and self-perceived capacity. “X” represents entry to, and exit from, the laboratory. “M” represents meals.

Table 1 Sleep Parameters Derived from Polysomnography for the Immediate, Delayed and Split Conditions

Variable	Immediate	Delayed	Split	Statistic	df	p
TST (min)	383.6 ± 22.3	384.0 ± 21.3	391.6 ± 17.6	F = 0.78	2,22	0.465
Stage N1 (min)	16.3 ±10.1	17.8 ± 6.6	15.5 ± 10.1	F = 0.61	2,22	0.541
Stage N2 (min)	160.0 ± 13.3	156.5 ± 27.6	145.5 ± 23.7	F = 1.63	2,22	0.221
Stage N3 (min)	124.3 ± 5.4^B,C	138.0 ± 6.6^A,C	149.5 ± 0.6^A,B	F = 11.46	2,22	<0.001
Stage R (min)	83.0 ± 26.0	71.8 ± 27.8	81.1 ± 27.9	χ^2 = 0.50	2	0.779
SOL (min)	3.2 ± 2.5^C	1.8 ± 1.2^C	5.5 ± 2.6^A,B	χ^2 = 21.17	2	<0.001
WASO (min)	33.6 ± 22.4^C	34.8 ± 21.0^C	18.6 ± 17.7^A,B	χ^2 = 8.00	2	0.018
Sleep efficiency (%)	91.2 ± 5.3	91.3 ± 5.0	93.0 ± 4.2	F = 0.70	2,22	0.498
Arousals (count)	65.0 ± 18.5	73.2 ± 17.3	66.6 ± 18.5	F = 1.22	2,22	0.301

Notes: ^ASignificantly different from the immediate condition (p<0.05), ^BSignificantly different from the delayed condition (p<0.05), ^CSignificantly different from the split condition (p<0.05). Normally distributed data were analysed using repeated measures ANOVA (test statistic: F); non-normally distributed data were analysed using the Friedman test (test statistic: χ²).

Abbreviations: TST, total sleep time; SOL, sleep onset latency; WASO, wake after sleep onset.

Figure 2 Sleep histograms representing the probability distribution of sleep stages in the immediate (top panel), split (middle panel) and delayed (bottom panel) conditions. Data represent the percentage of epochs scored as Stage N1 and Stage N2 sleep (light grey bars), Stage N3 sleep (white bars) and Stage R sleep (dark grey bars) in 5-min bins.

Figure 3 PVT reciprocal response time (top left panel), PVT lapses (top right panel), SAS reciprocal response time (middle left panel), SAS percentage of correct responses (middle right panel), DSST total substitutions attempted (bottom left panel) and DSST percentage of correct responses (bottom right panel) for each test session in the immediate (open circles), split (open triangles) and delayed (closed squares) conditions. Data are mean (± SEM).

Figure 4 Karolinska Sleepiness Scale (top left panel), Samn-Perelli fatigue scale (top right panel), VAS alertness (bottom left panel) and total mood disturbance (bottom right panel) for each test session in the immediate (open circles), split (open triangles) and delayed (closed squares) conditions. Data are mean (± SEM).