Reprint & Copyright 9 by 

Aerospace Medical Association, Washington, DC 

Sleep, Sleepiness, and Circadian Rhythmicity 

in Aircrews Operating on 

Transatlantic Routes 

HANS M. WEGMANN, ALEXANDER GUNDEL, MARTIN 

NAUMANN, ALEXANDER SAMEL, EDWIN SCHWARTZ, and 

MARTIN VEJVODA 

D.F.V.L.R. Institute of Aviation Medicine, Cologne; and 

Deutsche Lufthansa AG, Frankfurt, West Germany 

WEGMANN HM, GUNDEL A, NAUMANN M, SAMEL A, 

SCHWARTZ E, VEJVODA M. Sleep, sleepiness, and circadian 

rhythmicity in aircrews operating on transatlantic routes. Aviat. Space 

Environ. Med. 1986; 57(12, Suppl.):B53-64. 

This study was performed on B-747 aircrews operating on 

regular passenger flights between Frankfurt and the U.S. west 

coast (9 h time difference). In an initial phase, sleep behavior 

was surveyed by daily logs in 38 crewmembers. The results 

for the layover period indicate congruent sleep patterns with 

shifts in sleep onset distinctly less than 9 h. In comparison with 

preflight control data, sleep duration was significantly prolonged 

and, on average, no sleep deficits were experienced before 

commencing the return flight. The main part of the study consisted 

of polygraphic sleep recordings and multiple sleep latency tests 

(MSLT) applied to four complete cockpit crews (12 members 

total) in a baseline period, during layover, and after return 

to homebase. In addition, body temperature and ECG were 

continuously recorded. During layover, mean bed times were 

shifted by 4.5 h at maximum. Sleep was disturbed by early 

and prolonged awakenings which led to a reduction of sleep 

efficiency. In contrast, no sleep deficits nor increases in daytime 

sleepiness occurred. Night duty associated with the return flight 

caused sleep deprivation which conversely resulted in good sleep 

during the first night back in Germany. However, during the 

second night after return, impaired sleep was observed, at least 

in part caused by the rhythm disturbances. As predicted by our 

resynchronization model, ECG and rectal temperature recordings 

gave evidence for a desynchronization of the circadian system 

and an internal dissociation of different body functions. 

I N PRINCIPLE, our investigations were performed in 

two major phases. In a first step (Phase I) sleeplog surveys were obtained from crews operating on the 

FRA-SFO and FRA-LAX routes. The latter route was 

included since the flight schedules of both routes are 

Address reprint requests to: Dr. Hans M. Wegmann, DFVLR 

Institut fur Flugmedizin, Postfach 90 60 58, D-5000 K61n 90, West 

Germany. 

almost identical. The primary purpose of this phase was 

to obtain a better understanding of individual daily habits 

and strategies. As it subsequently turned out, these sleep 

surveys also provided valuable information about the 

quantity of sleep and its deviation from "normal." 

The second phase (Phase II) served as the main part 

of our investigation and consisted of a battery of tests 

and measurements applied to a group of 12 volunteers 

operating as B-747 crews on scheduled passenger flights 

between FRA and SFO. Like the other participating 

research groups, our central purpose was to study sleep 

in aircrews exposed to a time zone considerably different 

from their home base. However, since multiple time 

zone transitions are known to affect sleep by circadian 

rhythm disturbances, additional efforts were aimed at 

defining changes in the 24-h fluctuations of selected 

variables. Therefore, besides studying sleep-EEG and 

daytime sleep latency (MSLT) in the laboratory, we 

continuously recorded body temperature and ECG 

and collected continuous urine samples. The additional 

measurements were conducted not only during preduty and layover (L/O) periods, but also during flight. 

Furthermore, we attempted to learn more about flight 

crew readjustment to home time by continuing all 

measurements in the laboratory for approximately 2 

more days after return to FRA. 

Fig. 1 illustrates time lines and the general experimental design. At the present time, the results are limited 

to sleep-EEG, MSLTs, body temperature and ECG 

records. The chemical analysis of urinary hormones and 

electrolytes is still in process. 

MATERIALS AND METHODS 

During Phase I, 26 sleep logs were completed on 

the FRA-LAX route and 12 on the FRA-SFO route. 

Aviation, Space, and Environmental Medicine 9 December, 1986 B53 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

GMT 

I 

FLIGHT 

SLEEP-LOG ~JJJJ/JJJJJJ/~J/2 

SLEEP-EEG I~ ~[ 

I MSLT I ~ I 

ECG I.............J 

TEMPERATURE 

UR I N E v////////////~ 

FATIGUE 

J BASELINE J 

I J COLOGNE I 

! 

TH FR SA WE TH 

20 8 20 8 8 20 8 20 

I ' ' // ( i ' ' 

FR 

8 20 

I 

I 

I 

SA SU 

8 20 8 20 

I ! I 

8 

I 

I 

"////~//X//~ zC,///y//////~////////////////////~/////~////////////////////,~ 

I IF/~ FT/~l I B ~ p2-AI 

I B ~ BIi I I I 10[~ ~ I 

I----.~.-.............~//~-------------~ I 

I 

I 

I,,-~1 LAYOVER I-.(.., I POST RETURN J 

IFRA-I IS=0-I I 

ISFO I I FRAI COLOGNE I 

Fig. 1. Overview of time lines for the data collection of the flight schedule Frankfurt-San Francisco. 

The two groups were labeled "LAX" and "SFI," 

respectively. In Phase II, 12 additional logs were 

obtained from the experimental group, "SF2." 

The Phase I sleep surveys extended from 2 days 

before flight duty until 2 days after return to home 

base, whereas Phase II logs extended up to 6 days 

before duty commenced. To obtain better comparability 

between Phases, the additional 4 days were omitted 

from the analysis. Another difference was that Phase I 

crewmembers stayed in a hotel during their L/O and at 

home after the return flight. The experimental, Phase 

II group spent both periods in sleep laboratories. 

Phase II subjects were four complete cockpit crews (1 

Capt, 1 F/O, 1 F/E) for a total of 12 subjects who were 

assembled from a group of volunteer crewmembers. 

The age for captains and flight engineers ranged from 

44-53 years and for flight officers from 32-40 years. 

As Fig. 1 shows, measurements were conducted over a 

baseline period of 36 h in our Cologne sleep laboratory, 

in most cases during the week before the flight. All 

measurements were carried out in September 1984, 

with each crew leaving for SFO on Wednesday and 

returning to FRA on Saturday. Scheduled flight times 

were (in GMT) FRA:0810-SFO:1935 for the outgoing 

and SFO:2145-FRA:0830 for the home-going flight. 

After arriving at SFO the crews stayed together in 

separate rooms at the Stanford sleep laboratory for the 

48-h L/O period. After returning to FRA they were 

transported by helicopter to the Cologne laboratory, 

where they remained for an additional 44 h (post-return). 

Table I summarizes all variables and methods included 

in our investigation. Sleep EEG recordings were performed as described in detail in the introductory paper 

(Graeber et al.). Contrary to the other research groups, 

respiration and leg movements were not recorded in this 

study, and the pretrip measurements were conducted in 

the sequence: adaptation night, MSLTs, baseline night, 

i.e., the MSLTs did not follow the baseline sleep period. 

Seven baseline MSLTs were administered instead of six. 

ECG and rectal temperature were continuously recorded 

by means of Oxford Medilog tape recorders. Frequency 

analysis for the first harmonic was carried out on the 

B54 

TABLE I. OVERVIEW OF VARIABLES AND MEASURES. 

Mood Sleepiness Sleep Rhythmicity (24h) Workload 

Pre-Sleep MSLT (EEG, EOG) EEG Temperature ECG 

Scales 

SSS EOG ECG Catecholamines 

Fatigue Card EMG Urine Constituents 17-OHCS 

10-cm Scale Sleep Log 

Self-Ratings 

SSS=Stanford Sleepiness Scale 

Aviation, Space, and Environmental Medicine 9 December, 1986 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

heart rate and temperature data, according to Bliss (1), 

by shifting a 24-h window by 1-h intervals over the 

entire experiment. The results from this analysis were 

compared with values predicted by a model for the 

estimation of resynchronization after time-zone flights 

(13). Urine samples were collected in approximately 

2-h intervals and frozen for later chemical analysis. 

Subjective fatigue ratings (10) were obtained from the 

subjects at regular intervals during the awake periods. 

RESULTS 

Sleep log surveys: Figs. 2 to 5 present those results 

from the sleep log surveys which relate to the selfratings of time and duration of sleep. Quality of sleep 

was also assessed by five different rating categories. 

These data will be published elsewhere. 

The means of sleep-onset and -end shown in Fig. 2 

demonstrate that sleep timing under control conditions 

(days 1 and 2) can be considered quite normal. Thus, 

it can be concluded that these aircrews, when at home, 

go to bed at about 2200 GMT and get up at about 

0600 GMT. This is true for all three groups with only 

minor differences in the mean values. The sleep-end 

preceding flight duty on day 3 is earlier by 1-2 h, 

again in all three groups. As shown more clearly in 

the next figure, this results in a reduction of sleep 

duration, since sleep-onset on the prior evening is not 

adjusted correspondingly. During L/O, sleep timing is 

considerably shifted towards later hours, as would be 

expected by the time difference of 9 h between FRA and 

SFO/LAX. However, crewmembers do not shift their 

sleep periods completely, i.e., on the average groups 

LAX and SF1 delayed their sleep by not more than 

7-7.5 h (onset and end of sleep, respectively). Shifts 

of the experimental group are distinctly less (p<0.01), 

averaging a 5-h delay at the most. Thus, the experimental 

crews went to bed, fell asleep, and got up earlier than 

the crews staying at the hotel. After the return flight, 

sleep timing was immediately shifted back towards the 

habitual hours of sleep at home base. The experimental 

group (SF2) again differs from the others in that its 

mean times exhibit a slower readjustment, especially 

sleep onset (p<0.001). 

In summary, Fig. 2 demonstrates similar sleep behavior patterns of the three groups before, during and 

after the duty period. During L/O, shifts in sleep times 

on average were distinctly less than the difference in 

local time between FRA and SFO/LAX. 

Fig. 3 presents the results from the self-reports of sleep 

duration for the different groups. The similarity of the 

patterns is evident. Compared with the sleep period on 

day 1 (control night), there is consistently a significant 

reduction in sleep duration during the night immediately 

preceding flight duty. As demonstrated previously, these 

shorter sleep periods resulted primarily from the earlier 

wakeup times in preparation for the relatively early 

commencement of duty. Sleep duration is significantly 

extended in all groups during the first L/O, but only for 

the experimental group during the second night. After 

the return-flight, significant changes appear only twice: 

longer sleep on the first night for the LAX group and 

shorter sleep on the second night for the SF2 group. 

The pronounced reduction in the latter was, at least 

in part, caused by earlier arising at the end of the 

experiment due to an early pick-up time. As in the 

LAX group, a longer sleep duration occurred on the 

first post-return night for the SF1 group; however, this 

duration is not significantly different from control levels 

due to increased variance, probably caused by some 

substantially delayed return flights in this group. To 

summarize the findings of Fig. 3, it can be concluded 

that aircrews on the average slept less than "normal" 

on the night before commencing duty, but considerably 

more during the L/O period. 

Fig. 4 illustrates what we call "sleep balance," i.e., 

the sum of the deviations in sleep duration from 

control nights. Thus, the curves reflect sleep deficit 

or surplus accumulated each consecutive day over the 

entire experimental period. Again, the three groups 

exhibit almost identical patterns with a moderate sleep 

deficit on day 3, substantial surpluses during the L/O 

period, and dramatic deficits after the return flight. 

Obviously, these deficits result from the preceding night 

duty when normal sleep was not possible; however, if 

we take into account the afternoon sleep after arrival in 

DAYS 

1- 

2- 

3- 

1.. 

5- 

6- 

7- 

8- 

1- 

2- 

3 

4. 

5. 

6- 

7- 

8 

1- 

2- 

3. 

4. 

5. 

6. 

7. 

8- 

SLEEP 

o o BEGIN 

-= END 

GNT 

2b ' 2'4 ' Z ~ i ' 17 ' 1; 2b 

J - -- + I 

'~ "~ SFI 

n= 12 

GNT 

I - ~ + I 

/ / 

4, `r / 

~/ n= 12 

GMT 

;z i ' 6 1'2 ' 1; ~0 

Fig. 2. Subiective ratings of beginning and end of sleep 

during control, layover, and post-return nights. Presented are 

means (• S.D.) of the three different groups. (Numbers of days 

at the vertical axis refer to days beginning at 2400 GMT). 

Aviation, Space, and Environmental Medicine 9 December, 1986 B55 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

[hl 

11 

10 

9 

8 

7 

6 

LAX 

I 

1 

n= 26 

IIPIIE 

i 

I I 

345678 

4',+ 

SF1 n- 2 

1 23/.5678 

4-+ 

SF2 ** n=12 

! 

1 2 

I 

3/.5678 

Fig. 3. Subjective ratings of sleep duration during control, layover, and post-return nights (means • S.E.). *p <=0.05; **p<=O.01 

for differences from sleep period of day 1. 

[+h} 3 

CGN, the sleep balance approaches zero. Although the 2 

practical implication of computing sleep balance curves 1. 

may be debatable, they nevertheless demonstrate that 0 

aircrews usually attempt to get enough sleep and that ~ 

2" 

they succeed. 3. 

Finally, Fig. 5 combines the three groups' sleep ~. 

duration during the three major stages of the sleep log s. 

survey. From the distribution of sleep durations it can be I-h] 6 

concluded that under control conditions about 90% of 

sleep episodes were between 6 and 10 h. Sleep duration t.hl 3- 

was 5 h or less in only 5 out of 98 cases, indicating that 2 

1 severe sleep deficits do occur, although very rarely. This 0 

number of extremely short sleep periods remains the 1 

same throughout duty and post-duty days. In addition, 2 

for the 2 L/O nights the histogram clearly shows a shift a 

to longer sleep durations with maxima of 13 and 14 

s h in four cases. During the 2 post-return days, sleep t-h] 6 

periods show a tendency to normal length. The higher 

incidence in the 6-h class mainly reflects the enforced 

early termination of sleep during group SF2's last test 

night in Cologne. 

Sleep recording and MSLTs: In preparing to compare 

sleep parameters with baseline (B2) values, we first had 

to check the latter for outliers. Any value deviating 

by more than 2 S.D. (2-sigma-limit) from the group 

mean was defined as an outlier. Indeed, one subject 

exhibited REM sleep lower than this limit and wake 

time and time in bed (TIB) longer than this limit. In 

addition, his subjective sleep quality rating was below the 

2-sigma-limit. He complained about a headache during 

the baseline night and took two aspirin. As an apparent 

outlier, this subject was excluded when comparisons 

with baseline data were made. 

B56 Aviation, Space, and Environmental Medicine 9 December, 1986 

[+hl 3 

2 

1 

0 

I 

//~-~\ LAX n=2e 

2 3 ~ 5 6 "I 8 DAYS 

r 

/~..~\ SF1 n: 12 

~; i ~. ~ ~ # ~ DAYS 

SF2 n=12 

2 = ...... ...... 

S 

I-hi 6 

2 3 ~ 5 6 "] 8 DAYS 

Fig. 4. Sleep balance: accumulated deviations of subiectively 

rated sleep duration from control nights (day 1 and day 2). 

Values do not include short extra sleep periods (naps). Open 

circles and dashed lines represent sleep balance including sleep 

in the afternoon following return flight. 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

Inl 20 

L--__ 3O 

20 

10 

0 

In] 

30 

20 

10 

0 

nl 

3O 

20 

10 

2 CONTROL NIGHTS Zn= g8 

, i , , I , , i i , , 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 [h] 

2 LAYOVER NIGHTS Z n= 100 

12 

,] .... 212, J 

3 4 5 6 7 8 9 10 11 12 13 14 [h] 

i POSTRETUR Z n= 98 

,ll~l I I I i i'~iW]-~. 

2 3 ~ 5 6 7 8 9 10 ' ' ' ' ' ' ' 3 11 12 14 [h] 

Fig. 5. Histogram of subjectively rated sleep duration of all 

three groups together. Combined are two nights each from the 

control, layover, and post-return period. (Note: sleep period 

immediately preceding flight schedule not included). 

0 4 8 12 16 20 GMT 

BASELINE 

We 

w. 

Th SF02 :NAP i :N=g i Fr 

So ~ CGN 2 ~ 5u 

Su + CGN3 ~-~ Mo 

Fig. 6. Time schedule of sleep periods and flights. Time axis 

is chosen from 2000 to 2000 GMT. Bars for sleep periods show 

standard deviation for light off and on. Baseline recordings 

were taken several days before flight to SFO. 

The beginning and end of sleep periods were calculated as mean times (n--12) of lights-off and lightson and summarized in Fig. 6. Compared with baselines 

B1 and B2 when crewmembers went to bed at about 

2200 GMT, their mean bed times shifted by 3.2 h 

on the first L/O night (SFO1) and by 4.5 h on the 

second (SFO2). These values generally agree with those 

obtained from the sleep logs for the same period. For 

both sleep periods the average TIB was longer than 

during baseline or post-return. Get-up times showed 

considerable interindividual variability, with a standard 

deviation about twice that for baseline and post-return 

sleep. Before leaving Stanford for the return flight, nine 

subjects tried to nap, seven of them fell asleep. After 

the return flight, which was a complete night flight 

according to FRA time, all crewmembers went to bed 

in the afternoon (CGN1). On the following 2 nights, 

sleep was delayed by 1.9 h (CGN2) and 1.0 h (CGN3), 

compared to baseline. 

Fig. 7 shows the total sleep time (TST) as well as the 

percentages for different sleep stages. While TST was 

about 7.0 h for all night-sleep periods in Cologne (except 

for CGN3, as explained above), it increased to almost 

8.0 h during L/O. The afternoon sleep following the 

return flight (CGN1) had a mean TST of 3.5 h. REM 

sleep (%) was nearly constant for all sleep periods, 

Fig. 7. Mean percentage of total sleep time (TST) for sleep 

stages. Means (n= 12) are shown for seven sleep periods. Absolute 

TST value (rain) are given on top of the bars. 

Aviation, Space, and Environmental Medicine 9 December, 1986 B57 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

TABLE II. COMPARISON OF BASELINE (B2) SLEEP PARAMETERS (n= 11) WITH THOSE FROM 40-49-YEAR-OLD MALES 

(Williams) AND FROM ADAPTATION (B1), LAYOVER, AND POST-TRIP RECORDINGS. 

Source Minutes Percentage 

TIB TST S 1 $2 $3 + $4 REM 

B2 460.20 414.60 9.24 57.98 10.48 22.30 

Williams 429.10 389.10 8.07 a 58.41 a 9.13 a 24.39 a 

B1 494.50* 420.40 12.38" 57.86 6.90 22.85 

SFO1 572.30* * 477.50* * 11.93* 55.59 10.13 22.35 

SFO2 529.80** 461.90"* 10.19 57.48 9.38 22.96 

CGN1 219.10"* 208.70** 6.67 56.23 23.47** 13.63"* 

CGN2 469.80 429.90 7.22 56.84 8.32 27.61 * * 

CGN3 409.40 342.90 9.86 55.75 13.12 21.27 

*p<0.05; **p<0.01 

ao~ SPT values given by Williams were transformed to % TST 

except for a decrease during CGN1 and an increase in 

CGN2. While stage 2 sleep (%) was also fairly constant, 

slow wave sleep (stages 3 + 4, SWS) displayed a greater 

variability between sleep periods and a strikingly higher 

portion in CGN1. Large differences were also observed 

for stage 1. 

Table II compares the baseline (B2) sleep parameters 

of our group with data reported by Williams et al. (14) 

for a group of males (n = 10) ranging in age from 40-49 

years. TIB, TST, as well as sleep stage percentages do 

not differ significantly. In addition, this table compares 

all sleep periods with baseline sleep B2. As might be 

expected, the adaptation night (B1) produced a longer 

mean TIB (p<0.05) and more stage 1 sleep. During L/O 

nights, TIB and TST were significantly longer with more 

stage 1 sleep (%) in SFO1. The afternoon sleep CGN1 

had more SWS(%) and less REM sleep (%), while the 

following night (CGN2) showed enhanced REM sleep. 

,4 ~,\\\R 

k\\\\~ 7 4 ~\\\\~ 

k\\\\\ 5 t k\\\\\ 

k\\\\~ 4 4 k\\\\~ k\\\\~ 

kX~ 

o ' ~\~ B1 

MEDIAN NUMBER OF AWAKENINGS 

~XXXXXR ........ 

X\\\\\\ ,~.",",~,XX\. ~ 

B2 SF'O1 

\\\\\\\\ 

SF02 CGN1 CGN2 CGN3 

I00~ 

:I'" 

6O -[ I\\\\\\\ 

IX\X\\\\ 

,o ~ ~,\\\\\N 

k\\\\\\~ 

10 

0 , 

MEDIAN 

~,\\\\\\\ 

\\\\\\\\ 

....... ~X\\\\\) 

....... (((((((( 

\\\\\\\\ 

....... kXXXXXX\ 

B2 SFO I 

SLEEP EFFICIENCY (%) 

# 

\\\\\\\\ 

\\\\\\\\ 

))))?)) 

~XXX\\\) ....... 

SF02 CGN1 CGN2 

\\\\\ 

\\\\\ 

\\\\~ 

\\\\\ 

~X\\R 

~\\\\ 

~\\\\ 

\\\\\ 

\\\k~ \\\\\ 

\\\\~ 

CGN3 

Fig. 8. Median (n =12) latencies to the first 10 minutes of 

persistent sleep, to slow-wave sleep ($3), and to REM sleep. 

Significant differences from baseline values (B2) are indicated 

(*p<O.OS, **p<O.01. Wilcoxon-matched-pairs-signed-rank test). 

B58 Aviation, Space, and Environmental Medicine 9 December, 1986 

MEDIAN SUBJECTIVE SLEEP QUALITY 

20 

10 

0 . BI B2 

::::::: 

t,~\~\\ \\\\\\\\ 

SF01 SF02 

!!!!!! 

!!!!!! 

\\\\\~ 

CGN1 CGN2 CGN3 

Fig. 9. Sleep efficiency, number of awakenings, and subjective 

ratings of sleep quality for seven sleep periods. Significant differences from baseline (B2) are indicated (*p<O.OS, **p<O.01). 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

Median latencies to sleep onset, slow-wave sleep 

($3), and REM sleep are shown in Fig. 8. Though 

the interindividual variability was rather high, the 

following comparisons to baseline were statistically 

significant: longer latencies to sleep onset and REM 

during adaptation, reduced latency to $3 for the CGN1 

day sleep, and delayed sleep onset on the second postreturn night (CGN3). 

Fig. 9 presents median values of several sleep quality 

parameters. The number of awakenings varied between 

5 (CGN1) and 11.5 (B1). In comparison with B2, sleep 

was less efficient during B1, SFO1, and CGN3, but 

more efficient during CGN1. Subjective sleep quality 

ratings also suggest poorer sleep during B1, SFO1, 

and CGN3. Computations of correlations between sleep 

quality parameters and age revealed significant negative 

coefficients (r---0.63, p<0.05) for sleep efficiency 

during each L/O night, but not for total sleep time. 

Individual sleep patterns and MSLT results for 

baseline, L/O, and post-return are presented in Fig. 10. 

Most of the crewmembers underwent one SLT after 

arrival at Stanford and 5-9 MSLTs between the major 

sleep periods. For sleep SFO1, subjects went to bed at 

very different times, and this rank order remained almost 

the same for SFO2. One subject (row 6) had relatively 

long naps in addition to his short sleep periods and 

Fig. 10. Sleep pattern and multiple sleep latency test (MSLT). Sleep periods in black, wake times in white. Vertical lines between 

sleep periods represent MSLT; their height is sleep latency in 

minutes. (Top left=Baseline; top right--L/O; lower left--Postreturn). 

Aviation, Space, and Environmental Medicine 9 December, 1986 B59 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

Fig. 11. Mean MSLT after sleep 

periods B1, SFO1, SFO2, CGN2. 

20- 

rain 

0 

c 15- 

"6 

.._1 

C 

a 10- 

5- 

~ \. 

b \X 

V" . / ' 

o./ ol 

"o s 

I I I I I I I I | 

8 10 12 14 16 18 20 22 0 GNT 

after sleep period: 

[~1 O .... O 

SF0t = = 

SF02 o 

CGN2 ....... 

seemed to stay on home-base time. Shifts of sleep periods 

were more obvious for other subjects who exhibited 

longer TIB. As this figure clearly indicates, reduced 

sleep efficiency resulted from long waking times a) in 

the second half of SFO1 sleep and b) in the beginning 

of CGN3 sleep. 

Mean SLT values were calculated only if at least seven 

subjects performed the SLT at the corresponding time. 

In the home time zone, these mean values revealed 381 

a general pattern of long latencies immediately after J sleep, short latencies in the afternoon, and longer 36 

again in the early evening (Fig. 11). During L/O, 38] 

when measurements were extended until late evening, J the MSLT showed the typical biphasic contour. The 36 

longest onset latencies were always found after the main 

sleep periods (B1, SFO1, SFO2, CGN2), regardless 381 

of how far they were shifted. Comparison of MSLT 

latencies revealed the following significant differences 36 J 

(Wilcoxon test): a) increase between 1600 and 1800 381 

GMT for baseline (p<0.05) and L/O (p<0.10); b) 

increase between 1600 and 2000 GMT for baseline 36 1 

(p<0.05), L/O (p<0.01), and post-return (p<0.05); c) 38] 

and a decrease between 2000 and 2400 GMT for L/O 

(p<0.05). In addition, latencies of the MSLTs at 1800 36 

GMT were significantly different (p<0.05) between L/O 381 

and post-return. 36 ] 

Temperature and ECG: As compared with baseline 

data, temperature and heart rate curves revealed distinct 381 

phase shifts during L/O and after return to FRA. 36 ] 

The curves in Fig. 12 represent mean values from all 

experimental subjects. Computed minima (1), as well 38] 

as minima predicted by our model (13), are marked 36 J 

differently in the figure. Vertical lines illustrate where 

the minima would be expected if subjects had completely 

adapted to SFO time. 

The temperature rhythm was shifted by 3.75 h on 

the first and by 5 h on the second day of the L/O 

period (both relative to baseline), while after return to 

home base the shift was 3.25 h relative to the last day 

in SFO (or 2.75 h relative to baseline). The rhythm of 

heart rate was shifted even more: 6.25 h on the first 

day in SFO and 7.0 h on the second; after return to 

FRA a shift of 6.0 h relative to SFO2 occurred, which 

corresponds to a time difference of 1 h relative to the 

baseline rhythm. 

TEMPERATURE [~ 

HEART FREQUENCY [1/MIN] 

120] J,1 i 

I I 

. ~ 

12~ zEzg- WE 

60~ TH 

12 ~ ~-.,,_.z.,~U~ a ~,,, v i~~~ ~ FR 

60 J -"~- 

120] I I 

' #9 SU 

12011 / I 

60 I ~' ~ MO 

~. GMT 

20 22 24 02 04 06 08 10 12 14 16 18 20 

9 actual and 9 predicted minima of temperature 

v actuol and a predicted minima of heart frequency 

Fig. 12. Means for temperature (upper curves) and heart rate 

(lower curves) before, during and after flights. Vertical lines 

indicate position of minima during baseline and after complete 

shift by 9 h (solid lines: temperature; dashed lines: heart rate). 

B60 Aviation, Space, and Environmental Medicine 9 December, 1986 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

TABLE III. ESTIMATED 24 h MEANS AND AMPLITUDES OF HEART RATE 

AND TEMPERATURE COMPUTED FROM AVERAGE CURVES [After Bliss (1)]. 

SOURCE HEART RATE TEMPERATURE 

(L-min-I) (~ 

Mean Amplitude Mean Amplitude 

B1/B2 68.5 13.0 36.8 0.55 

SFO1 71.5 19.5 36.75 1.00 

SFO2 72.5 17.5 36.8 0.60 

As a consequence of the different adjustment speeds, 

internal dissociation can be observed. The phase difference between heart rate and temperature rhythms 

was -1 h during baseline periods and changed to + 1.5 

h during the first and + 1.0 h during the second day in 

SFO. Due to the faster readaptation of the heart rate, the 

phase difference became -2.75 h after return to home 

base. No actual minima from harmonic analysis are given 

for the return-flight day, because of the irregularities 

in the sleep-wake cycle. According to FRA time this 

flight was a total night flight. Even if related to the 

shifted circadian rhythm (delay by 5 h), it must still be 

considered as night duty, at least in part. Inspection of 

the curves demonstrates that, though the first circadian 

trough occurred in the second part of the duty period, 

heart rate and temperature already increased again about 

2 h before landing. 

The periodical decrease of heart rate and temperature 

every 2 h during awake time in Fig. 12 was most 

likely caused by the reduction of activity during 

MSLTs. Compared with the heart rate oscillations, the 

temperature fluctuations were delayed by 20-30 min. 

While the 24-h means of the circadian rhythms show 

only minor variation, the amplitudes are considerably 

higher during L/O as compared with baseline and postreturn periods (Table III). In our view, this is mainly 

caused by a masking effect. From the longer sleep 

durations one could expect an increase in amplitude since 

longer periods of inactivity result in longer sections of 

lower values in heart rate and temperature rhythms. At 

the same time, this would also lead to a decrease in the 

24-h mean, but in our case such an effect is compensated 

by the higher physical activity of most subjects during 

the day at Stanford (e.g., bicycling and jogging). Of 

course, these activities enhance the rhythm amplitudes 

even more by adding sections of values higher than 

normal to the rhythm curves. 

In order to interpret the circadian results in more 

detail, shifts in acrophases of temperature and heart 

rate as well: as those predicted by our model are 

presented in Fig. 13, along with the subjects' mean 

daily bedtimes. All parameters indicate a clear shift 

towards the corresponding hours of the new time-zone 

(by a delay during L/O and by an advance after return 

to CGN). However, heart rate adapts faster, mainly 

due to the simultaneous shift of the rest-activity cycle. 

Temperature acrophases shift more slowly, and their 

adjustment pattern corresponds well with the bedtimes, 

except for day CGN3. Fig. 13 also demonstrates that 

changes in temperature rhythm acrophase, after either 

westward or eastward flight, can be correctly predicted 

by our model of resynchronization. 

DISCUSSION 

Our experimental design was based initially on the 

following hypothesis: Due to the considerable time 

difference between FRA and SFO, aircrews performing 

duty on this route would suffer from rhythm disturbance 

of their circadian system. As a direct consequence, they 

would also experience sleep difficulties, a problem which 

has repeatedly been a matter of serious concern among 

aircrews and safety researchers (5,7,8). Furthermore, 

sleep difficulties would be manifested by sleep loss and 

reduced sleep quality, both in terms of subjective ratings 

and objective EEG recordings. 

0 5 10 15 &T [H] 

I I I I l i l i i I I i I I 

0 

V 

.i. 

'.!.,', \ 

,iy . 

,,,y\ 

../ 

/ / / _-- 

/ / .~.---- 

I/ il 

li ii 

t 4 

I I I I I I I I I 

5 10 

MODEL 

ONSETOF TIMEINBED 

TEMPERATURE 

HEART FREQUENCY 

BIlB2 

SFO1 

SFO2 

CGN2 

CGN 3 

I I I I I 

15 ~T [HI 

Fig. 13. Shifts in acrophases relative to baseline position. 

Aviation, Space, and Environmental Medicine 9 December, 1986 B61 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

Sleep log analysis: Clearly, the results from our sleeplog surveys do not support the above hypothesis. In 

contrast, there is convincing evidence that our pilots 

slept significantly more during the L/O period and 

did not suffer at all from sleep loss, as compared 

with their normal sleep habits at home base. It is 

not possible to determine whether this was achieved 

by conscious attempts or by efforts and conditions 

beyond the subjects' direct control. From personal 

communications, however, we are inclined to conclude 

that the majority of the pilot population is well aware of 

this problem and takes serious measures to get enough 

sleep. No doubt, the results from the sleep-log surveys 

demonstrate that they succeed; however, the findings 

presented in this paper do not rule out the possibility 

that sleep deficits may occur in individual cases. The 

presented results deal only with computed means and, 

thus, merely reflect average behavior. There are already 

indications that severe sleep deficits may be experienced 

by some crewmembers. In at least five cases, sleep was 

5 h or less during L/O as well as during control and postreturn periods (with a 3-h minimum in one case). A 

more detailed analysis is planned to settle this question 

of individual problems. 

There is another, more general, but also quite 

unexpected result that the sleep-log surveys are disclosing. Initially, all participating research groups were 

concerned about whether the sleep laboratory would 

be an adequate setting to obtain realistic information 

about "true" L/O behavior in the hotel environment. 

Comparison of the three sleep-log groups reveals strong 

evidence that we were well "on the safe side," in 

essence for two reasons: a) the patterns of sleep timing 

and duration were almost identical; in fact, statistical 

analysis (Kruksal-Wallis test) did not detect any general 

difference when the data sets (entities of 8 days) as 

a whole were compared, and b) during the first L/O, 

night sleep duration in the laboratory was significantly 

shorter than in the hotel environment (U-test); again, 

this was in contrast to what had been expected. Despite 

the quiet, isolated surroundings of the sleep facility, our 

subject group did not sleep longer than aircrew staying in 

the commercial atmosphere of the city hotel. In addition, 

during both post-return nights, the laboratory group 

reported distinctly shorter sleep durations than the other 

groups sleeping at home. Thus, the data clearly refute 

the argument that sleep deficits could be anticipated 

in the realistic world even though they had not been 

observed in the laboratory. 

Of course, conclusions drawn from subjective ratings 

may give cause for criticism. However, subjective 

estimates of sleep duration, i.e., time between onset 

and end, correlate well with objective measurements. 

This is not necessarily true for the amount of sleep, 

since number and time of awakenings are frequently 

misjudged, thus leading to major discrepancies between 

subjective and objective assessments of total sleep time. 

Theoretically, our sleep-log data could have indicated 

longer sleep periods despite a decrease in the amount 

of sleep, if our subjects had suffered from longer 

awakenings than accounted for by the surplus in sleep 

duration. In fact, the sleep-EEG recordings in our 

experimental group disclosed considerably prolonged 

awake periods during L/O sleep. Nevertheless, total 

sleep time was distinctly longer than under baseline 

conditions. To us, there appears to be little evidence 

that this should be different in the two other groups. 

In particular, the impressive and consistent similarities 

between the three groups in almost all sleep-log results 

support this view. 

Sleep recording and MSLT analysis: As a prerequisite 

for discussing details of the sleep-EEG and MSLT 

results it is important to know whether there are 

any differences between crewmembers' usual habits 

and their behavior in the laboratory, and how such 

differences may influence final conclusions about the 

study. 

Each time subjects left the sleep laboratories, questionnaires were administered asking for general sleep 

quality and a comparison between their usual sleeping 

conditions and those of the laboratory. In general, 

the answers to each question were equivalent after 

the baseline, L/O, and post-return periods. On a 5- 

point scale from "very poor" to "very good," the 

subjects consistently rated their sleep quality as being 

good. Quantity of sleep, daytime drowsiness, and 

quantity of meals were judged as comparable with the 

usual conditions. Upon leaving the Cologne laboratory 

after the post-return phase, all crewmembers were 

interviewed. Six claimed that their sleep was better than 

at home, and six reported no difference. The improved 

sleep was attributed to the darkness and silence of the 

laboratory and to the absence of family disturbances. In 

contrast to what we inferred from the sleep-log surveys, 

these findings could mean that conclusions regarding 

sleep quality drawn from the experimental results should 

be rather conservative with regard to sleep in the usual 

world, where flight crews are sometimes faced with a 

more disturbing environment. 

The experimental part of the sleep investigations 

revealed a clear pattern of sleep periods with only minor 

individual differences. During L/O, the onset of the 

two main sleep periods was shifted ahead by 3.2 and 

4.5 h, respectively, as compared with baseline data. 

Our results cannot distinguish whether these shifts were 

due to a phase shift of an autonomous circadian sleep 

rhythm, or whether they reflect a conscious compromise 

between increased fatigue and an adjustment to the 

social environment of the new time zone. If the crewmembers delayed sleep completely by 9 h, they would 

be much more tired during the presleep hours. Even 

with only a partial sleep delay, Stanford Sleepiness Scale 

(SSS) ratings and MSLT results indicate that the subjects 

were more tired before L/O sleep than before baseline 

or post-return sleep. 

After the return flight, which according to FRA local 

time was a complete night flight, crewmembers retired 

in the afternoon for a recovery sleep of several hours. 

For the night-sleep periods, they went to bed more than 

1 h later than during baseline. As there was no social 

need, this behavior may be explained by a circadian 

phase delay resulting from the preceding adjustment to 

the SFO time zone. However, another reason is also 

conceivable: it might be assumed that recovery sleep in 

B62 Aviation, Space, and Environmental Medicine 9 December, 1986 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

the afternoon leads to delayed tiredness in the evening 

and consequently to a later sleep time. 

Objective sleep quality may be conceived as a matter 

of the amount and continuity of sleep. Accordingly, the 

typical disturbance of sleep during the adaptation night 

was manifested by decreased sleep efficiency, a higher 

number of awakenings, a longer sleep-onset latency, and 

a longer latency to REM sleep. Despite this impaired 

sleep quality, there was no increase of overall sleepiness 

during the day. In fact, the MSLT results provided no 

indication of an abnormal increase in sleep tendency 

during any phase of the study. 

On the first L/O night subjects slept less efficiently 

and rated their sleep subjectively worse. The efficiency 

was reduced by relatively long awakenings during the 

second half of the night. Probably, the circadian system 

forced them to awake too early, e.g., because they felt 

hungry or had to use the bathroom. Possibly due to 

training or experience, they were able to fall asleep 

again and to compensate somewhat for the effects of 

shifted sleep by staying in bed longer. Thus, at the end 

they got even more total sleep than during the baseline 

night. The sleep disturbances seen during SFO1 were 

not as pronounced for SFO2. 

However, from correlational analysis, we found that 

difficulties in sleep continuity during L/O increased with 

age, so that older crewmembers had to stay in bed longer 

than younger ones in order to get enough sleep. 

The majority of the crewmembers took a nap before 

the return flight home. This short extra sleep most likely 

improved alertness for the following night shift (6,9). 

During the return flight the subjects incurred a sleep loss 

which may account for the good sleep experienced during 

the afternoon and first night after arrival in Germany. 

The afternoon sleep was characterized by a rebound 

of SWS, i.e., a short latency to stage 3 sleep and more 

SWS(%) than observed during baseline. During the 

following night a rebound of REM sleep was observed. 

These effects are well known as consequences of sleep 

deprivation. During the second night, objective as well 

as subjective sleep quality was reduced, very likely due 

to rhythm disturbances, some of which were detected 

in MSLT and body temperature. 

The MSLT results closely reflect the 24-h profiles 

reported by Richardson et al. (11). Nevertheless, the 

interpretation of MSLT results turned out to be more 

complicated. At least two factors seem to influence 

daytime sleepiness. The first is related to the time since 

the preceding sleep. Thus, long sleep latencies were 

observed whenever subjects had recently awakened from 

a major sleep regardless of time of day. After pilots 

awoke, they were unlikely to fall asleep during the 

following SLT. A second factor reflects a circadian 

influence on sleep tendency. It is characterized by 

relatively high sleepiness around midday and an increase 

in sleep latency in the late afternoon. The increase 

occurred at the same time (GMT) during the baseline 

and L/O periods. Consequently, we conclude that the 

underlying sleepiness rhythm might have shifted too 

slowly to be disclosed after the westbound flight. The 

observation of an SLT-rhythm delay after the return 

flight supports the view that the delayed nocturnal sleep 

in Cologne is related to the observed delay in the 

circadian rhythmicity of other physiological functions. 

Rhythm disturbances: As expected, our results 

provided evidence that the time-zone transition associated with flight duty on the FRA-SFO route 

leads to a) desynchronization of internal body time 

from the external timing system, and b) an internal 

dissociation between the circadian rhythms of different 

body functions. Both effects influence sleep behavior. 

This was most clearly shown by the early and prolonged 

awakenings of the first L/O sleep period. Most likely 

these awakenings were triggered by the circadian system, 

which was out of phase with the new local time 

by an advance of more than 5 h (according to the 

acrophase of the temperature rhythm). Due to progressive synchronization, awakenings occurred at later hours 

and became shorter or disappeared during the second 

nocturnal sleep period. In contrast to awakenings, sleeponset time is influenced by other factors in addition to 

circadian rhythmicity, e.g., activation, conscious efforts, 

and in particular the duration of the preceding awake 

period. Therefore, the advance of sleep-onset during 

L/O may not reflect the "true" shift of the underlying 

rhythm, but more probably is the result of several 

influences. This could also explain our findings from 

the sleep surveys that sleep-onset time in the laboratory 

was earlier than in the hotel. 

For the post-return period we were also able to 

demonstrate a desynchronization of circadian rhythms 

from local time. In contrast to the SFO L/O, however, it 

was a delay and the extent was less pronounced (ca. 2 

h). Theoretically, this again should affect sleep; but 

awakenings would be expected at the beginning of the 

sleep period, or a delayed onset of sleep should occur. 

As already mentioned, our EEG data confirmed this 

assumption for the second night, whereas the findings 

for the first nocturnal sleep were confounded by the 

effects of sleep deprivation and the preceding afternoon 

sleep. 

Our rhythm results reveal one other important 

operationally relevant fact. Due to the relatively short 

L/O period, synchronization with SFO time was not 

completed. In fact, the circadian system had only shifted 

by about 5 h before the return flight commenced. Thus, 

readaptation to home-base time would be comparable 

to conditions after the transition of five time zones. 

As a result, desynchronization on the second post-return 

day was not more than about 2.5 h, which is below 

the limit (3 h) that is accepted as critical in terms of 

operational significance (13,15). 

CONCLUSIONS 

We were able to show that the time zone transition 

associated with FRA-SFO flight duty leads to a 

desynchronization of the circadian system. According to 

our hypothesis, rhythm disturbances would cause major 

difficulties for sleep quality and quantity. However, 

from our subjective and objective sleep data we must 

conclude that the observed desynchronization produced 

only moderate effects upon sleep. During L/O, early 

and extended awakenings led to a reduction of sleep 

Aviation, Space, and Environmental Medicine 9 December, 1986 B63 
SLEEP, SLEEPINESS, & RHYTHMICITY--WEGMANN ET AL. 

efficiency, but did not cause sleep deficits. Sleepiness 

during the diurnal phase was not elevated, but quite 

normal. Night duty during the return flight caused sleep 

deprivation which in turn resulted in good sleep during 

the first night at homebase; however, impaired sleep 

occurred on the second night, at least in part caused 

by desynchronization. Nevertheless, resynchronization 

to homebase time appears fast enough that pilots can 

achieve a reasonable readjustment before commencing 

flight duty again. 

Obviously, these conclusions cannot be generalized. 

In the present form, our results consider only mean 

values and do not address individual cases where the 

situation may be far less favorable than on the average, 

Finally, our conclusions apply only to a duty schedule 

that is relatively short and not especially complex. There 

are other duty patterns that require operations with 

much more complex schedules involving many more 

days away from home base and more transit stops in 

different time zones. From these we may anticipate a 

quite different picture as to sleep problems and rhythm 

disturbances. Finally, it should be mentioned that the 

present results fit well into the line of our previous 

studies in aircrews and complement the results that have 

been obtained from short-haul (4) as well as from longhaul flight schedules (2,3,12). 

ACKNOWLEDGMENTS 

The authors are very much obliged to the staff of the Stanford 

University Sleep Research Center who carried out the sleep and 

MSLT recordings during the L/O period in the U.S. We wish to 

express our sincere gratitude to the participating crewmembers for 

their exceptional motivation and outstanding cooperation. Special 

thanks go to Ute Brandl, Gabriele Kraus, and Paul Esser 

for their valuable assistance. This research was supported by 

the U.S. National Aeronautics and Space Administration (NASA 

Cooperative Agreement NCC2-302 with Stanford University School 

of Medicine) and the German Ministry of Transport. 

REFERENCES 

1. Bliss CL. Statistics in biology. New York: McGraw Hill, 1970. 

2. Klein KE, Bruner H, Ruff S. Untersuchungen zur Belastung 

des Bordpersonals auf Fernflugen mit Dusenmaschinen. 

Bericht uber die Ergebnisse auf der Nordatlantikroute. DLRForschungs-bericht 1965; 65-44:1-68. 

3. Klein KE, Bruner H, Holtmann H, Rehme H, Stolze T, Steinhoff 

WD, Wegmann HM. Circadian rhythm of pilot's efficiency 

and effects of multiple time zone travel. Aerospace Med. 

1970; 41:125-32. 

4. Klein KE, Bruner H, Kuklinski K, Ruff S, Wegmann HM. 

Bericht uber die Auswertung von Untersuchungen am 

fliegenden Personal der DLH zur Frage der beruflichen 

Beanspruchung auf der europaischen Kurzstrecke. Koln-Porz: 

DFVLR-Institut fur Flugmedizin. Interner Bericht 1974; 335 

-74/2:1-42. 

5. Klein KE, Wegmann HM~ Significance of circadian rhythms 

in aerospace operations, AGARDograph No. 247. NeuillySur-Seine: NATO-AGARD, 1980. 

6. Mullaney DJ, Kripke DF, Fleck PA, Johnson LC. Sleep 

loss and nap effects on sustained continuous performance. 

Psychophysiology 1983; 20:643-51. 

7. Nicholson AN. Duty hours and sleep patterns in aircrew 

operating world-wide routes. Aerospace Med. 1972; 43:138 

-41. 

8. Nieholson AN, Stone BM, Borland RG, Spencer MB. 

Adaptation to irregularity of rest and activity. Aviat. Space 

Environ. Med. 1984; 55:102-12. 

9. Nicholson AN, Pascoe PA, Roehrs T, Roth T, Spencer MB, 

Stone BM, Zorick F. Sustained performance with short evening 

and morning sleeps. Aviat. Space Environ. Med. 1985; 56:105 

-14. 

10. Pearson RG, Byars GE. The development and validation 

of a checklist for measuring subjective fatigue. USAF 

School Aerospace Med. Tech. Rept. 1956; SAM-TR-56-115. 

Randolph AFB, TX. 

11. Richardson GS, Carskadon MA, Orav EJ, Dement WC. 

Circadian variation in sleep tendency in elderly and young 

adult subjects. Sleep 1982; 5(Suppl. 2):82-94. 

12. Wegmann HM, Klein KE, Goeters KM, Samel A. 

Flugmedizinische Untersuchungen zur DLH Non-Stop-Route 

Frankfurt-Rio de Janeiro. Koln-Porz: DFVLR-Institut fur 

Flugmedizin. Interner Bericht 1981; 316-81-01:1-29. 

13. Wegmann HM, Klein KE, Conrad B, Esser P. A model 

for prediction of resynchronization after time-zone flights. 

Aviat. Space Environ. Med. 1983; 54:524-7. 

14. Williams RL, Karacan I, Hursch CJ. EEG of human sleep. 

New York: John Wiley and Sons, 1974. 

15. Zweite Durchfuhrungsverordnung zur Betriebsordnung fur 

Luftfahrtgerat (2.DVOLuftBo). Frankfurt (Main): Bundesanstalt fur Flugsicherung, 1981. 

B64 Aviation, Space, and Environmental Medicine 9 December, 1986