KUMPULAN MAKALAH ERGONOMI
EDITOR :
Dr. I G. N. Susila, M.Kes
KONGRES NASIONAL XI DAN SEMINAR ILMIAH XIII IKATAN AHLI ILMU FAAL INDONESIA DAN INTERNATIONAL SEMINAR ON
ERGONOMICS AND SPORTS PHYSIOLOGY DENPASAR, 14 – 17 OKTOBER 2002
ERGONOMI
KUMPULAN MAKALAH YANG DIPRESENTASIKAN DALAM KONGRES NASIONAL XI DAN SEMINAR ILMIAH XIII IKATAN AHLI ILMU FAAL INDONESIA
DAN INTERNATIONAL SEMINAR ON ERGONOMICS AND SPORTS PHYSIOLOGY
DI DENPASAR, 14 – 17 OKTOBER 2002
EDITOR :
Dr. I G. N. Susila, M.Kes
UDAYANA UNIVERSITY PRESS
DENPASAR - BALI ISBN NO. 979 – 8286 – 54 – 5
Udayana University
International Union of Physiological Sciences
Organizing Committee
IAIFI
737
How well do international aircrew sleep during layovers?
Greg Roach, Tracey Sletten, David Darwent, Drew Dawson
Centre for Sleep Research, University of South Australia
PO Box 232, Woodville SA 5011, AUSTRALIA
email: [email protected]
ABSTRACT
Aims. Disruption to the internal body clock caused by rapid time zone changes may
interfere with international aircrews’ sleep during layovers. The extent of this disruption
may depend on the direction of flight and the number of time zones crossed. The aim of
the current study was to compare the length and quality of sleep episodes obtained by
aircrew during layovers in Asia, Europe, and the US, with sleep obtained at home in
Australia.
Method. A total of 71 international aircrew (66 male, 5 female) wore wrist activity
monitors and kept sleep/wake and flight/duty diaries for at least 15 consecutive days
while they worked their normal roster patterns. Data from the activity monitors and
sleep/wake diaries were used to determine sleep length, sleep efficiency, sleep quality,
and the restorative value of sleep.
Results. Factorial ANOVA indicated that region and time of sleep onset had significant
main and interaction effects on all four dependent variables. In particular, sleep length
was shorter, sleep efficiency was lower, self-rated sleep quality was lower, and the
restorative value of sleep was lower during layovers in Asia, Europe, and the US, than at
home in Australia.
Conclusions. The current data demonstrate the difficulty that aircrew face in obtaining
sleep during layovers after transmeridian flight. If aircrew are unable to sufficiently
recover during layovers, they may experience relatively high levels of work-related
fatigue during homebound flight.
Keywords. sleep length, sleep quality, fatigue, time zones, aircrew.
738
BACKGROUND
Aircrew often experience relatively high levels of fatigue because they work irregular
schedules that involve long work periods, early departures, late arrivals, night work, and
rapid time zone transitions (Samel et al., 1995). This is an important safety issue given
that aircrew fatigue has been identified as a contributing factor in several near-misses,
incidents, and fatal accidents in civil aviation (Coleman, 1986; Caesar, 1986; Green,
1985; Cabon et al., 2000; Lyman & Orlady, 1980).
The sleep disruption associated with transmeridian flight (i.e. flight across several time
zones) may be a major contributor to aircrew fatigue (Gander, et al., 1998a, 1998b).
Sleep is disturbed by transmeridian flight because the sleep/wake cycle (and several other
physiological variables) fluctuate rhythmically with a 24-hour period that is
endogenously generated by the circadian timing system (Carskadon & Dement, 1975,
1977; Lavie, 1986; Lavie & Scherson, 1981; Lavie & Zomer, 1984). The most important
zeitgebers (i.e. time givers) for the human circadian system are the light/dark cycle and
social cues (Klein & Wegmann, 1980; Wever et al., 1983). Transmeridian flight causes a
rapid phase shift in these zeitgebers to which the circadian system is unable to instantly
re-entrain (Wever, 1980). The resultant desynchrony can lead to difficulty initiating or
maintaining sleep, and may also cause daytime sleepiness, decreased alertness, and
impaired performance (Klein & Wegmann, 1980; Loat & Rhodes, 1989; Manfredini et
al., 1998; Wegmann & Klein, 1985; Winget et al., 1984; Wright et al., 1983).
The aim of the current study was to determine the impact of transmeridian flight on the
quantity and quality of sleep that aircrew obtain by comparing their sleep at home (on the
east coast of Australia) with their sleep during layovers in Asia, Europe, and the US.
Previous studies have shown that the rate of resynchronisation of the circadian timing
system with local zeitgebers depends on the number of time zones crossed and the
direction of flight. Typically, resynchronisation is faster if more time zones are crossed
and if flight is in a westward direction (Aschoff et al., 1975; Harma et al., 1994; Klein &
Wegmann, 1980; Suvanto et al., 1990; Winget et al., 1975). Thus, it was hypothesised
that (i) sleep episodes would be shorter and sleep quality would be lower during layovers
than at home, and (ii) sleep episodes would be shorter and sleep quality would be lower
during layovers after eastward flight than during layovers after westward flight.
739
METHODS
Participants
A total of 71 international aircrew (27 captains, 19 first officers, 25 second officers; 66
male, 5 female) participated in the study after responding to recruitment notices posted on
notice boards and to the employer company’s intranet. All participants signed a consent
form that signified their informed consent, confirmed their volunteer status, and stated
that they understood their rights and obligations. All participants were assigned a unique
identification code to ensure their anonymity. Participants did not receive any additional
payment for participating in the study above their usual salary. The study was approved
by the University of South Australia Human Research Ethics Committee using guidelines
established by the National Health and Medical Research Council of Australia.
Procedure
Participants each wore wrist activity monitors and kept sleep/wake and flight/duty diaries
for at least 15 consecutive days while they worked their normal roster patterns. In the
sleep/wake diary, participants recorded sleep location, sleep start and end times, pre- and
post-sleep fatigue levels, and self-rated sleep quality for all sleep periods (including
naps). In the flight/duty diaries, participants recorded flight start and end times, flight
origin and destination, and pre- and post-flight fatigue levels.
Measures and Data Analysis
Measures extracted from the activity monitor records and sleep/wake diaries included:
§ Sleep Length: period between sleep onset time and wake up time, less awakenings.
§ Sleep Efficiency: the percentage of time in bed that is actually spent sleeping.
§ Sleep Quality: self-rating of sleep quality (reverse-scored on a scale of 1-5 such that
higher scores indicate higher quality).
§ Restorative Value of Sleep: difference between self-ratings of pre-sleep fatigue level
and post-sleep fatigue level (higher positive scores indicate greater restorative value).
Separate two-way factorial analyses of variance (ANOVA) were conducted to determine
the effects of region (home, Asia layover, Europe layover, US layover) and time of sleep
onset (local time in 6-hour bins) on the various measures of sleep length and sleep
quality. Post hoc analyses were conducted with Fisher’s PLSD where required.
740
RESULTS
Factorial ANOVA indicated that region (F3,1952=9.42, p<.0001) and time of sleep onset
(F3,1952=209.85, p<.0001) had significant main effects, and a significant interaction effect
(F9,1952=17.82, p<.0001), on sleep length (Figure 1). Post hoc analyses revealed that sleep
length was significantly shorter during layovers than at home: sleeps at home were 1.14
hours longer than sleeps during layovers in Asia (p<.0001), 2.22 hours longer than sleeps
during layovers in Europe (p<.0001), and 0.95 hours longer than sleeps during layovers
in the US (p<.0001). Post hoc analyses also revealed that sleep length was significantly
shorter for sleeps that began during the daytime (i.e. 0600-1800h) than for sleeps that
began during the night-time (i.e. 1800-0600h) (all p<.0001).
Factorial ANOVA indicated that region (F3,1899=7.84, p<.0001) and time of sleep onset
(F3,1899=20.28, p<.0001) had significant main effects, and a significant interaction effect
(F9,1899=4.15, p<.0001), on sleep efficiency (Figure 2). Post hoc analyses revealed that
sleep efficiency was significantly lower during layovers than at home: sleep efficiency at
home was 3.03 percent greater than sleep efficiency during layovers in Asia (p<.0001)
and 3.84 hours percent greater than sleep efficiency during layovers in Europe (p<.0001).
Post hoc analyses also revealed that sleep efficiency was significantly lower for sleeps
that began during the daytime than for sleeps that began during the night-time (all p<.01).
Factorial ANOVA indicated that region (F3,1874=3.96, p<.01) and time of sleep onset
(F3,1874=8.20, p<.0001) had significant main effects, and a significant interaction effect
(F9,1874=2.24, p<.05), on sleep quality (Figure 3). Post hoc analyses revealed that sleep
quality was significantly poorer during layovers in Asia and Europe than at home (both
p<.001), and that sleep quality was significantly poorer for sleeps that began during the
daytime than for sleeps that began during the night-time (all p<.0001).
Factorial ANOVA indicated that region (F3,1952=3.42, p<.05) and time of sleep onset
(F3,1952=9.50, p<.0001) had significant main effects, and a significant interaction effect
(F9,1952=2.44, p<.01), on the restorative value of sleep (Figure 4). Post hoc analyses
revealed that the restorative value of sleep was significantly lower during layovers in
Asia, Europe, and the US than at home (all p<.0001), and that the restorative value of
sleep was significantly lower for sleeps that began during the daytime than for sleeps that
began during the night-time (all p<.0001).
741
Figure 1. Mean sleep length (± s.e.m.) as a function of time of sleep onset for sleeps (a) at home, (b) during layovers in Asia, (c) during layovers in Europe, and (d) during layovers in the US.
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
0
1
2
3
4
5
6
7
8
0
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3
4
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7
8
00-06 06-12 12-18 18-00
Time of Sleep Onset (local time)
a. Home
b. Asia
c. Europe
d. USA
Slee
p Le
ngth
(ho
urs)
742
Figure 2. Mean sleep efficiency (± s.e.m.) as a function of time of sleep onset for sleeps (a) at home, (b) during layovers in Asia, (c) during layovers in Europe, and (d) during layovers in the US.
00-06 06-12 12-18 18-00
Time of Sleep Onset (local time)
a. Home
b. Asia
c. Europe
d. USA
60
65
70
75
80
85
90
60
65
70
75
80
85
90
60
65
70
75
80
85
90
60
65
70
75
80
85
90
Slee
p Ef
ficie
ncy
(%)
743
Figure 3. Mean sleep quality (± s.e.m.) as a function of time of sleep onset for sleeps (a) at home, (b) during layovers in Asia, (c) during layovers in Europe, and (d) during layovers in the US.
00-06 06-12 12-18 18-00
Time of Sleep Onset (local time)
a. Home
b. Asia
c. Europe
d. USA
2.8
3.0
3.2
3.4
3.6
3.8
4.0
2.8
3.0
3.2
3.4
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3.8
4.0
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3.2
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4.0
2.8
3.0
3.2
3.4
3.6
3.8
4.0
Slee
p Qu
ality
(re
vers
e-sc
ored
)
744
Figure 4. Mean restorative value of sleep (± s.e.m.) as a function of time of sleep onset for sleeps (a) at home, (b) during layovers in Asia, (c) during layovers in Europe, and (d) during layovers in the US.
00-06 06-12 12-18 18-00
Time of Sleep Onset (local time)
a. Home
b. Asia
c. Europe
d. USA
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
1.0
1.2
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1.6
1.8
2.0
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1.0
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2.0
2.2
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1.0
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1.6
1.8
2.0
2.2
2.4
Rest
orat
ive
Valu
e of
Sle
ep
745
DISCUSSION
Before the results are discussed, it is important to note that (i) the current study represents
a preliminary analysis of data collected in an on-going project, and (ii) one of the main
dependent variables in the current study was the length of sleep episodes, rather than the
total amount of sleep obtained per day. (For a detailed examination of the total amount of
sleep obtained by aircrew at home and during layovers, refer to the paper by Darwent et
al. in this issue.)
The first hypothesis, that sleep episodes would be shorter and sleep quality would be
lower during layovers than at home, was supported. Specifically, sleep length was
shorter, sleep efficiency was lower, self-rated sleep quality was lower, and restorative
value of sleep was lower during layovers in Asia, Europe, and the US, than at home in
Australia. This sleep disruption may have occurred because the circadian timing system
is unable to immediately re-entrain to local zeitgebers after transmeridian flight (Wever,
1980). Consequently, international aircrew face a dilemma: if they attempt to sleep
during local night, their sleep occurs out of phase with their internal body clocks, but if
they attempt to sleep during local day, their sleep occurs out of phase with local time cues
(i.e. environmental, social).
The second hypothesis, that sleep episodes would be shorter and sleep quality would be
lower during layovers after eastward flight than during layovers after westward flight,
was not supported. In fact, sleep episodes were longer and sleep efficiency was greater
during layovers in the US (after eastward flight) than during layovers in Europe (after
westward flight). This was unexpected given that eastward flight is usually considered
more disruptive than westward flight (Aschoff et al., 1975; Harma et al., 1994; Klein &
Wegmann, 1980; Suvanto et al., 1990; Winget et al., 1975). This curious finding may be
explained by the fact that westward flight from Australia to Europe involved a greater
time zone transition than eastward flight from Australia to the US.
The current data demonstrate the difficulty that aircrew face in obtaining sleep during
layovers after transmeridian flight. If aircrew are unable to sufficiently recover during
layovers, they may experience relatively high levels of work-related fatigue during
homebound flight.
746
REFERENCES
Aschoff, J., Hoffman, K., Pohl, H., & Wever, R. (1975). Reentrainment of circadian rhythms after phase-shifts of the zeitgeber. Chronobiologia, 2(1), 23-78.
Cabon, P., Bourgeois-Bougrine, S., Mollard, R., Coblentz, A. & Speyer, J.J. (2000). Fatigue of short-haul flight aircrew in civil aviation. In: S. Hornberger, P. Knauth, G. Costa, S. Folkard (Eds.), Shiftwork in the 21st Century, 79–85. Peter Lang, Frankfurt am Main, Germany.
Caesar, H. (1986). Long-term statistics and their impact on safety management and operational procedures. In: Proceedings of the 39th International Air Safety Seminar, 11–23. Flight Safety Foundation, Arlington.
Carskadon, M. A. & Dement, W. C. (1975). Sleep studies on a 90-minute day. Electroencephalography and Clinical Neurophysiology, 39(2), 145-155.
Coleman, R. M. (1986). Wide Awake at 3:00 A.M. By Choice or by Chance? New York: W.H. Freeman and Company.
Gander, P. H., Gregory, K. B., Connell, L. J., Graeber, R. C., Miller, D. L., & Rosekind, M. R. (1998a). Flight crew fatigue IV: Overnight cargo operations. Aviation, Space, and Environmental Medicine, 69(9 Suppl.), B26-B36.
Gander, P. H., Gregory, K. B., Miller, D. L., Graeber, R. C., Connell, L. J., & Rosekind, M. R. (1998b). Flight crew fatigue V: Long-haul air transport operations. Aviation, Space, and Environmental Medicine, 69(9 Suppl.), B37-B48.
Green, R.G. (1985). Stress and accidents. Aviation Space and Environmental Medicine, 56: 638–640. Harma, M., Laitinen, J., Partinen, M., & Suvanto, S. (1994). The effect of four-day round trip flights over
10 time zones on the circadian variation of salivary melatonin and cortisol in airline flight attendants. Ergonomics, 37(9), 1479-1489.
Klein, K. E. & Wegmann, H. M. (1980). Significance of Circadian Rhythms in Aerospace Operations (NATO AGARDograph No. 247). Advisory Group for Aerospace Research and Development, NATO, London.
Lavie, P. & Scherson, A. (1981). Ultrashort sleep-waking schedule. I. Evidence of ultradian rhythmicity in 'sleepability'. Electroencephalography and Clinical Neurophysiology, 52(2), 163-174.
Lavie, P. & Zomer, J. (1984). Ultrashort sleep-waking schedule. II. Relationship between ultradian rhythms in sleepability and the REM-non-REM cycles and effects of the circadian phase. Electroencephalography and Clinical Neurophysiology, 57(1), 35-42.
Lavie, P. (1986). Ultradian rhythms in human sleep. III. Gates and 'forbidden zones' for sleep. Electroencephalography and Clinical Neurophysiology, 63(5), 414-425.
Loat, C. E. & Rhodes, E. C. (1989). Jet-lag and human performance. Sports Medicine, 8(4), 226-238. Lyman, E.G. & Orlady, H.W. (1980). Fatigue and Associated Performance Decrements in Air Transport
Operations (NASA contract NAS2-10060). Battelle Memorial Laboratories, Aviation Safety Reporting System, Mountain View.
Manfredini, R., Manfredini, F., Fersini, C., & Conconi, F. (1998). Circadian rhythms, athletic performance, and jet lag. British Journal of Sports Medicine, 32(2), 101-106.
Samel, A., Wegmann, H. M., & Vejvoda, M. (1995). Jet lag and sleepiness in aircrew. Journal of Sleep Research, 4((S2)), 30-36.
Suvanto, S., Partinen, M., Harma, M., & Ilmarinen, J. (1990). Flight attendants' desynchronosis after rapid time zone changes. Aviation, Space, and Environmental Medicine, 61(6), 543-547.
Wegmann, H. M. & Klein, K. E. (1985). Jet-lag and aircrew scheduling. In S. Folkard & T. Monk (Eds.), Hours of Work: Temporal Factors in Work Scheduling (pp. 263-276). Chichester: John Wiley & Sons.
Wever, R. (1980). Phase shifts of human circadian rhythms due to shifts of artificial zeitgebers. Chronobiologia, 7(3), 303-327.
Wever, R. A., Polasek, J., & Wildgruber, C. M. (1983). Bright light affects human circadian rhythms. Pflügers Archiv, 396(1), 85-87.
Winget, C. M., Bond, G. H., Rosenblatt, L. S., Hetherington, N. W., Higgins, E. A., & DeRoshia, C. (1975). Quantitation of desynchronosis. Chronobiologia, 2(3), 197-204.
Winget, C. M., DeRoshia, C. W., Markley, C. L., & Holley, D. C. (1984). A review of human physiological and performance changes associated with desynchronosis of biological rhythms. Aviation, Space, and Environmental Medicine, 55(12), 1085-1096.
Wright, J. E., Vogel, J. A., Sampson, J. B., Knapik, J. J., Patton, J. F., & Daniels, W. L. (1983). Effects of travel across time zones (jet-lag) on exercise capacity and performance. Aviation, Space, and Environmental Medicine, 54(2), 132-137.
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