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Figure 1, A representative diurnal cycle for body temperature, heart rate or performance. Below are time scales

corresponding to time zones 7 hours east and west of the home zone. Departure and arrival times are given
for non-stop jet flights across seven time zones in both eastward and westward directions.

3





wan greater the strain of flying.TM
i

frequency. The effects of shift rotation upon
~mental capability and manual dexterity have
been observed in industry.

Travel Implications

In 1952, Strughold described a resynohroni
zation of diurnal rhythms relative to air travel
through many time zones.* Twenty-one years
earlier, Wiley Post reported his anticipation of
time zone physiological problems due to long-
distance flights.%/ This is the first recorded in-
stance of time zone effects relative to air travel.
Mr. Post’s successful record-breaking, globe-
girdling flights appear to have been successful,
in part, due to his recognition of the adverse
effects of diurnal rhythm disruption on flight
performance. He spent months learning how
to eat and sleep at varying times in order to
break his regular habits. In 1933 Mr. Post set
a new around-the-world record flying alone in
his single engine Lockheed Vega, the Winnie
Mae. He had readjusted his “biologic clock”
so his body was out of phase when he left New
York but in phase when he completed one half
of his journey over Russia. Because of this, he
claims he was able to stay alert without stimu-
lants.

Since the disruption of circadian rhythms
may adversely affect human performance, a
number of studies have .been conducted in an
attempt to determine the point at which airline

ilots become impaired to an unsafe degree.

(German scientists have determined, from psycho-

physiologic studies of transatlantic airline pilots,

that the greater the interval between the flight

departure time and the pilots’ “activity peak”,
They also
nfer from their data that performance failures
and accidents are more likely to occur during
the “hour of lowest resistance”. As a result of
his study, we understand that crews were re-
scheduled with consideration given to night
departure times and multiple landings with
intercontinental flights.

French aeromedical physicians have reviewed
responses of airline pilots undertaking flights
through six time zones (Paris to New York)
and found that (1) younger pilots suffered less
than older pilots, and (2) that the hours of
flight from east to west or vice versa should be
weighted with an incremental coefficient that

would give pilots more credit than for hours
flown in a north-south direction,”

British aeromedical scientists have accom-
plished biomedical studies on transoceanic pilots
prior to, during, and after their flights.2° The
investigators found that heart rates varied di-
rectly with (1) work load during flight, (2) the
specific airplane (peak landing heart rates for
the Boeing 707 averaged 128 per minute; for
the VC-10, 100), (3) the nature of the approach
aids and airfields (higher with limited aids, or
more marginal airfields), and (4) the weather.
These data, when coupled with circadian rhythm
disruption, have obvious implications governing
scheduling in relation to departure times and
recovery periods after flight across several time
zones,

To assess biologic changes in occupants not

concerned with aircrew duties, Flink and Doe
measured 17-hydroxycorticosteroid, sodium, and
potassium levels in 3-hour urine aliquots in a
subject: who was flown from Minneapolis to
Korea (9 hour time zone difference).* The in-
vestigators found that the diurnal biochemical
excretion patterns synchronized gradually with
Korean time, reaching a time displacement of
9 hours from Minneapolis time by the 11th day,
a rate of adjustment of approximately 1 hour
per day.
Atudies conducted by the FAA have indicated
that several days are required for complete re-
synchronization of the biological rhythms after
flights through several time zones; disruption
did not occur on a north-south flight. Subjec-
tive fatigue was reported initially after all
flights.Impaired psychological performance was
demonstrated only after the long east-west flight.
Re-adaptation to the “hoyhe” time zone was more
rapid in most. cases. @ FAA has been con-
ducting fatigue studies relative to pilots since
1935, but only since the jet age of the past
decade have time zone effects become of major
importance. With the SST, it should be pos-
sible to schedule crews for round trips the same
day and keep them adapted for one time zone.
Except for possible longer trips with less lay-
overs, the effects of supersonic travel on pas-
sengers should not be significantly more (or
less) disrupting than present jet travel.

Figure 1 shows a representative (body tem-
perature, heart rate or performance) diurnal


curve. A time scale for a time zone to which
an individual is adapted is shown above the
curve. Time scales for zones 7 hours east and
west are shown below the curve.

If a traveler leaves on a non-stop flight from
New York to Rome (a 7-hour flight, crossing
seven time zones) at 1830 hours, he will arrive
at 0830 local time, but 0130 home time. He is
thus biologically ready to sleep and not hungry.
However, with sufficient conscious effort, he can
immediately engage in business meetings, tours,
meals and social functions, but probably at less
than peak performance for the first 24 hours.

The return flight, after full adaptation to the
local zone, leaves at 1100 hours and arrives at
1415 after a 10-hour flight. Sleep, which is
“due” in 2 or 3 hours, may be delayed for a
while but the “biologic clock” starts its awaken-
ing process by late evening and sound sleep, once
attained, is hard to maintain. Sleep cannot be
achieved by the conscious effort which permitted
acceptable performance after arrival in Rome.
In addition, the stomach is very time conscious
and hunger for breakfast, which is “due” at
0100, may add further to the discomfort. Adap-
tation on westward flights can thus be expected
to take longer than on eastward flights of the
same length.

These are but two examples given in general
terms. There are obviously many variables
which affect any individual’s experienced symp-
toms. These include times of departure and ar-
rival, length of flight, direction of flight, layovers,
travel experience, stress, age, physical condition,
food and liquor consumed inflight, sleep inflight,
climate changes, and the new social environment.
The normal temperature and heart rate diurnal
curves can be affected by the social environment.

A recent paper by Hartman and Cantrell
recommends appropriate laboratory experiments
and field studies to determine more adequately
the loss in piloting skill as a result of alterations
in cyclical physiological functions.’ To this end,

the Civil Aeromedical Institute is now planning
the conduct, and/or support, of such studies.

Ameliorating Time-Zone Effects: Conclusions

Ordinarily the long-distance east-west or west-
east air traveler cannot prevent entirely the
effects of “time-zone fatigue”. The methods of
ameliorating such effects are similar for members
of aircrews or passengers.

1. If the life habits, environmental factors and
“clock” time at the destination are kept similar
(by simulation) to those of the origin, the bio-
logic rhythms will not be disrupted greatly.
This approach is not practical in most cases.

2. With the advance knowledge that time-zone

rephasing of biologic rhythms will begin at the
destination and may require several days for
most of the affected cycles to rephase, the trav-
eler should plan to depart on a long east-west
or west-east trip in as rested a physical state as
possible, Businessmen and tourists should allow
a day at the destination for accomplishing the
initial rephasing of cycles prior to engaging
fully in the demanding (and often excessively
fatiguing) activities associated with international
travel. If this is not possible, flights should be
scheduled which arrive before nightfall in order
to get a good night’s sleep.
VA 8. A long-distance traveler should definitely
pace himself during the asynchronous period if
he wishes to receive the least biological and
mental strain.

4, Heavy increases in consumption of rich and
“inaccustomed foods and alcohol are often con-
comitants of foreign travel. Since such con-
sumptions are stresses in themselves, combining
these with biological asynchrony is doubly
fatiguing.

5. Physical fatigue is one of the best means
of inducing sleep. Exercise is particularly bene-
ficial to permit sleep at local times before
“normal” bedtimes,


AM 68-8

CIRCADIAN RHYTHMS AND THE EFFECTS
OF LONG-DISTANCE FLIGHTS

Stanley R. Mohler, M.D. ~
J. Robert Dille, M.D. ~
Harry L. Gibbons, M.D.

Approved by Released by
Stentey A MeN o-hlew 2 wo
Srantey R. Mouter, M.D. P. V. Smmcex, M.D.

Cmer, ArROMEDICAL Feperat Arr Surceon

Avpuications Division

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
_ Office of Aviation Medicine



6.

~

. Cuites, W. D.:

. Funk, E. B., and Doz, R. P.:

. ELALBERG, F,:

REFERENCES

Board of Trade, Great Britain: Prevention of
Excessive Fatigue in Aircrews. Appendix to C. A.
Form 1238. August 8, 1967.

A Note on Diurnal Cycles, Work
Schedules and Time Zones, (In preparation.)
Cortiss, C. J.: The Day of the Two Noons. Wash-
ington: Association of American Railroads, 1949.
Effect of Sudden
Time Displacement by Air Travel on Synchronization
of Adrenal Function. Proc. Soc. Baptl. Biol. Med.
100: 498-501, 1959.

Temporal Coordination of Physio-
logic Function. Cold Spring Harbor Symp. Quant.
Biol. 25: 289-310, 1960.

Hatsere, F.: Physiological Rhythms. In: Physio-
logical Problems in Space Exploration. Edited by

J. D. Hardy. Springfield, Illinois: Charles C.
‘Thomas, 1964,
Harrman, B. O., and Canrrett, G. K.: Sustained

Pilot Performance Requires More Than Skill. Aero-
space Med. 88: 801-803, 1967.

Havry, G. T., and Apams, T.: Phase Shifts of the
Human Circadian System and Performance Deficit
During Periods of Transition. Office of Aviation
Medicine, Federal Aviation Agency. Reports AM
65-28 (East-West), AM 65-29 (West-East), and
AM 65-30 (North-South), 1965.

. Howirr, J. S. et al: Flight Deck Work Loads in

Civil Air Transport Aircraft. Ministry of Defence,
Great Britain. FPRC Report 1240, August 1965.

10. Howrrr, J. S., et al; Second Report on Flight Deck
Work Loads in Civil Air Transport Aircraft. Min-
istry of Defence, Great Britain, FPRC Report 1264,
December 1966.

11. Kuen, K. E., Bruner, H., and Rurr, S.:  Investi-
gation Regarding Stress on Flying Personnel in
Long-Distance Jet Flights. Zeitschrift fur Flugwis-
senschaften 14: 109-121, 1966.

12, Lavernue, J., Laronratne, E., and Lapnang, R.:
Subjective Effects of Time Shifts (An Inquiry Among
Flight Personnel of Air France), Revue de Medi-
cine Aeronautique 4: 30-36. 1965.

18, Mitts, J. N.: Human Circadian Rhythms. Physiol.
Reviews 46: 128-171, 1966.

14, Pincus, G.: A Diurnal Rhythm in the Excretion
of Urinary Ketosteroids by Young Men. J. Clin.
Endocrinol. Metab. 3: 195-199, 1943.

15. Post, W., and Garry, H.: Around the World in
__Eight Days. London: John Hamilton, Ltd., 1981.

16. ;uGHoLD, H.: Physiological Day-Night Cycle
‘After Global Flight. J. Aviation Med. 23: 464-478,
1952.

17. Warsx, J. F., and Mistax, H.: Diurnal Variation
of Critical Flicker Frequency. J. General Psych.
75: 167-175, 1966.

18. Wurrencap, R. E.: Memorandum for Annual Re-
port. Medical Section, Civil Aeronautics Adminis-
tration, July 19, 1985.



ACKNOWLEDGMENT

Dr. Mohler is Chief, Aeromedical Applications Division, Office of Avia-
tion Medicine, Federal Aviation Administration, Washington, D.C. Dr. Dille
is Chief, Civil Aeromedical Institute, and Dr. Gibbons is Chief, Aeromedical
Research Branch, Civil Aeromedical Institute, FAA, Oklahoma City, Okla-
homa. Prepared for the October 23-27, 1967, meeting of the American Public
Health Association, Miami Beach, Florida.

Qualified requesters may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific and
Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151


CIRCADIAN RHYTHMS AND THE EFFECTS
OF LONG-DISTANCE FLIGHTS

The term “circadian” (derived from the Latin
circa dies, about a day) was introduced by Hal-
berg in 1959. It refers to a time period which
imprecisely approximates 24 hours in duration,
ranging from 20 to 28 hours.’ It is commonly
applied to rhythmic biologic functions which
are geared to (1) an internal “biologic clock”
(endogenous rhythm), (2) the intrinsic sleep-
wake cycle, and/or, (3) exogenous influences
(the solar day-night cycle, temperature, social
environment, etc.). Examples of circadian
rhythms are diurnal variations in body tempera-
ture, heart rate, performance, ‘adrenocortical
secretions, eosinophils,® and evaporative water
loss.®

Tone of the grievances against the King con-
tained in the Declaration of Independence, July
4, 1776, reads: “He has called together legisla-
tive bodies at places unusual, uncomfortable, and
distant .... for the sole purpose of fatiguing
them... .”. Thus, the adverse effects of time
and odd hour schedules on the subjective and
physical state of individuals helped bring about
the Revolution.

Air transportation has highlighted the rela-
tionship of circadian rhythms to the subjective
and physical well-being of travelers, especially
when they rapidly traverse more than four time
zones. One country is currently proposing to
amend its air crew flight time limitations as
follows: “In the event of there being a time
zone change of four or more hours between the
place of departure and the place where duty
ends, the subsequent rest period should be not
less than twelve hours” This paper will de-
scribe some of the implications of such flights
for the air traveler.

Prior to November 18, 1883, there were no
standard time zones® More than one hundred
different time zones existed in-the U.S., based on
sun” time in individual towns as determined by

the best local estimate of “noon”. Michigan had
as many as 27 local times. Scheduling coordina-
tion problems led the U.S. railroads to spearhead
the adoption of standard time zones jn 1883. The
United States Government gave a legal sanction
to the time zone principle by passing the Stand-
ard Time Act on March 19, 1918, adopting the
“four-zone” system of the railroads.

Biological Aspects

Pincus first described a diurnal periodicity
for the excretion of urinary 17-ketosteroids.*
‘Adrenocortical secretions begin to enter the blood
stream just prior to waking and serve to arouse
the sleeper. The plasma cortisol level begins to
rise about 0400, reaches a peak at about 0800,
and declines to about one-half this level by late
evening. These plasma cortisol levels are re-
flected in increased urinary 17-hydroxycorti-
costeroid, 17-ketosteroids, aldosterone, potassium,
and water excretion 2 to 4 hours later.

here are diurnal variations in body tempera-
ure. The lowest values occur about 4 hours
after midnight during sleep and are thought to
result from variations in cutaneous blood flow
(as a heat loss mechanism) and body metabolism
(which decreases with sleep). The highest
values occur between 1500 and 1700.

Breathing rates change on a circadian basis
(diminishing in amplitude and rate during
sleep) ; the vital capacity diminishes after mid-
night (possibly due to an increased blood volume
in the pulmonary vessels). Zhe heart rate gen-
erally reaches a daily peak during the 1500-1800
period.*

Diurnal changes in human performance have
also been noted. Halberg has reported a 70%
increase in errors in reading gas meters after
midnight.* Chiles has found cycling in perform-
ance in several studies? Walsh and Misiak”
have reported diurnal variation of critical flicker