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: greg.roach@unisa.edu.au

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

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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

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Slee

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ficie

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(%)

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

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(re

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)

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

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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

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