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Oklahoma City.

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Fieure 2. Rectal-temperature recordings obtained in Oklahoma City and overseas from two subjects who participated
in the East-West and West-East flights,



2. Palmar Evaporative Water Loss. Plotted
with the rectal-temperature curves in Figure 1 are
mean values for resting palmar evaporative water
loss. As is revealed by the preflight plottings,
this function also appears to manifest circadian
periodicity with a phase closely associated with
that of rectal temperature. This association, how-
ever, is markedly affected by the time displacement
incurred in that no consistent form of periodicity
is manifested by palmar evaporative water loss
during any of the days in Rome.

Since assessments were made only during the
1500- and 1900-hour periods on Day +1 for the
East-West flight, a similar schedule was required
for the flight being reported.

3. Blood Pressure. During preflight, systolic
pressures evidence a circadian periodicity refer-
enced to local time, whereas diastolic pressures do
not. Yet, beginning with Day +6, periodicity
is consistently demonstrated by the diastolic-pres-
sure curves. In contrast, the subsequent curves
of systolic pressure do not show clearly a return
to the periodicity noted during preflight.

4. Heart Rate. Circadian periodicity is also
revealed by the preflight values plotted for heart
rate, and its phase also is seen to be closely asso-
ciated with that of internal temperature. Its
time lag, however, may be somewhat longer since
a complete shift of phase does not appear to occur
until Day +8.

5. Respiratory Rate. In contrast to heart
rate, respiratory rate does not demonstrate a well-
defined or consistent periodicity except for the
last 8 days in Rome.

6. Numerical Ability. Despite a considerable
amount of practice given prior to the preflight pe-
riod of assessment, the effect of practice is clearly
eivdent up to the last day in Rome (Day +12).
Against this trend of gradual improvement, it is
difficult to detect deficit except for Day +2, which
does show clearly a decrement.

7. Reaction Time. Reaction-time values
shown in Figure 1 represent the average speed of
appropriate manual response to a variety of stim-
uli and stimulus conditions throughout each day
of assessment. Using preflight values for com-
parison, reaction time is seen to increase substan-
tially (i.e, become slower) during Day +1 and
also Day +2. On Day +3, reaction time de-
creases (improves in speed) to slightly below
preflight levels. Analyses of the variance attrib-
utable to replicated days of assessment reveal that

the increment of reaction time on Day +1 and
Day +2 is not statistically significant.

8. Decision Time. The values plotted for
decision time in Figure 1 represent the daily mean
speed of decision as defined. As for reaction time,
decision time increases (becomes slower) on Day
+1, returns toward the preflight level on Day
+2, and, except for Day +12, remains about this
level for the remaining days of assessment in
Rome. In using the above-mentioned model for
analysis of variance, the increase in decision time
noted for Day +1 was not statistically significant.

9. Subjective Fatigue. The index of subjec-
tive fatigue was scaled from “extremely fatigued”
to “extremely alert”; the higher the daily mean
values plotted in Figure 1, the more fatigued the
subjects felt themselves tobe. The level of fatigue
reported by the subjects is seen to be high on Day
+1, lower on Day +2, and, on Day +4, equal to
the level reported during preflight. This demon-
strated increment in fatigue was found to be
highly significant (P=0.001).

10. East-West and West-East Comparison.
In Figure 2 are plotted hourly rectal-temperature
recordings obtained from two subjects (CC and
TB) who participated in both flights (Manila and
Rome). Missing data for TB are attributable to
the interference of the technical duties that this
particular subject had to perform. Inspection of
TB’s rectal-temperature curve for the first and
seconds days in Rome reveals the opposable lags
demonstrated by Figure 1. Completion of the
phase shift is shown on Day +6. In Manila, the
curves of this subject are characterized by the ex-
pected lag to the left’on Days +1 and +2. Com-
pletion of the phase shift, however, is difficult to
determine because of the marked increase in am-
plitude seen to occur in Day +6. Nevertheless,
the probable time for the phase shift is not appre-
ciably different from that of the flight to Rome.
Essentially the same form of curves was obtained
from subject CC; shift of phase appears to have
been completed on Day +6 in Rome and, perhaps,
on Day +4 in Manila.

B. Back Shift. Time of departure for the re-
turn flight to Oklahoma City was 1300 hours
(Rome time), total time in transit was 18-14
hours, and arrival time was 0030 hours (CST).
The first day of postflight assessment followed the
day of arrival in Oklahoma. This difference must
be taken into account when comparing the primary
and back shifts.


Figure 8 presents data for determining the ef-
fects of time displacement occasioned by the flight
back to Oklahoma City.

1. Physiological Functions. Circadian peri-
odicity appears to be sustained for only two of the
functions assessed, rectal temperature and heart
rate. For both, a complete phase shift back to the
Jocal time of Oklahoma is not shown by any of the
postflight days of assessment.

2. Psychological Functions. A pronounced
increase in reaction time is shown by Day +1, and
this increment persists during the remaining days
of assessment; however, this increment is not sta-
tistically significant. Increase in fatigue is re-
ported on Day +1 (P=0.001) but on Day +5,
fatigue has returned to the level reported during
preflight. In contrast, decision time decreases
slightly but not statistically significantly during
Days +1 and +2.

3. Comparison of East-West and West-Hast
Back Shifts. Rectal temperatures obtained from
subjects CC and TB following return to Oklahoma
City are presented by Figure 4. For TB, the
phase lag is seen to persist through Day +5 fol-
lowing return from Rome; following return from
Manila, the phase lag is equally persistent. In-
terpretation is difficult owing to the substantial
difference in the time of day that temperature
peaks during the two preflight assessments (Rome
and Manila). Phase lag is also revealed by the
curve of CC following his return from Rome, and
this persists through Day +5. In contrast, a com-
plete shift of phase would appear to have occurred
following his return from Manila.

IV. Discussion.

Interpretation of the bidirectional effects of
time displacement reported here and earlier * must
take into consideration the influence of individual
differences and of voluntary activity associated
with the attempt to retain normal living habits
throughout the course of biomedical assessment.
As has been revealed, mean values of rectal tem-
perature obtained in Rome indicate that phase
shift did not appear complete until Day +6. In
comparison, it was found that the shift of phase
was completed on Day +4 in Manila. Within
the limits of the two factors mentioned above,
phase shifts for East-West and West-East dis-
placements may be the same.

The differential time lag of the primary phase
shifts manifested by the periodicity of heart rate

during the two flights may also be attributable to
the same factors; however, the lag difference is
more extreme. In Rome, phase shift was not com-
plete until Day +8, whereas, in Manila, shift of
phase was completed on Day +4. In Rome, heart
rate and rectal temperature were dissociated with
respect to phase, whereas, in Manila, the phases of
heart rate and rectal temperature were not dissoci-
ated during the period of transition. If this is a
real bidirectional difference, an explanation is not
available.

A more notable difference between the Hast-
‘West and West-Bast flights is that revealed by
psychological deficit and its duration. The curves
of reaction time, decision time, and subjective
fatigue obtained in Rome show a high degree of
agreement with those of the Manila flight; that is,
increase in each of these three functions occurs
on Day +1, but this increase or deficit is of very
short duration in comparison with the time lags
seen for the physiological functions. For the
Rome flight, however, tests of statistical signif-
icance indicate that only the increment in fatigue
can be accepted as a real or experimentally induced
difference, suggesting that, despite increased sub-
jective fatigue, psychological performance was
unaffected by the joint effects of time displacement
and prolonged flight. Why psychological deficit
occurred in Manila but not in Rome may be an-
swered by the flight yet to be reported, which was
designed to appraise the effects of prolonged
flight alone.

The most apparent notable difference, perhaps,
is revealed by the back shift. Here, following re-
turn from Rome, a complete shift of phase was
not revealed by any of the physiological func-
tions during any of the days of postflight assess-
ment. Following return from Manila, a complete
shift of the phase of rectal temperature was seen
on Day +1. Since such a bidirectional difference
is difficult to reconcile with the probability that
little or no bidirectional difference may exist be-
tween the primary phase shifts of rectal tempera-
ture, the temperature recordings of each subject
were individually inspected. It was found that
a complete back shift of phase did occur in the
case of two subjects but not for the other two.
This does not resolve the question of bidirectional
difference. It does indicate, however, that even
for those functions manifesting periodicity of
assumed stability, larger samples of subjects are
required.



AM 65-29

PHASE SHIFTS OF THE HUMAN CIRCADIAN SYSTEM
AND PERFORMANCE DEFICIT DURING THE
PERIODS OF TRANSITION:

II. West-East Flight

G. T. Hauty, Ph. D.

T. Adams, Ph. D.
Approved by Released by
J. Rosurt Diz, M.D. P. V. Simcnt, M.D.
Curr, Crvit ABROMEDICAL Feperat Arr SuRGEON
INSTITUTE
December 1965

FEDERAL AVIATION AGENCY
Office of Aviation Medicine





V. Summary and Conclusions.

At periodic intervals throughout the biological
day, biomedical assessments were made for a week
prior to jet flight to Rome, for 12 days at Rome,
and for a week following return to Oklahoma City.
The following conclusions were derived :

(1) Rapid translocation through the seven time
zones effected a primary shift of phase of the
circadian periodicity manifested by physiological
functions. For rectal temperature and heart rate,
the time required for completion of phase shift
was from 4 to 6 days and 6 to 8 days, respectively.

(2) Return back to the environment of origin
also effected a shift of phase manifested by internal
temperature that, for two subjects, was completed
in less than 5 days and, for the two remaining
subjects, was not completed in 5 days.

(8) Increase in fatgue occurred during the pri-
mary period of transition and following return
to the environment of origin, but psychological
performance was not impaired during either
period.

(4) Duration of the fatigue was shorter than
the time lag of the physiological phase shifts.

REFERENCES

. Aas, T. FunKHovsER, G. E., and Kennan, W. W.:
Measuremeans of Evaporative Water Loss by a Thermal
Conductivity Cell. J. Appl. Physiol. 18: 1291, 1963.

2. Apams, T., FunkHouser, G. E., and Kenpati, W. W.:
A Method for the Measurement of Physiological Evapo-
rative Water Loss. ©.A.R.I. Report No. 63-25, Federal
Aviation Agency, 1963.

8, Haury, G, T., and Apams, T.: Phase Shifting of the
Human Circadian System. In Circadian Clocks,
Aschoff, J., ed., North-Holland Publishing Co., Amster-
dam, 1965.

4, Haury, G. T., and Apams, T.: Phase Shifting of the
Human Circadian System and Performance Deficit
During the Periods of Transition: I. Hast West Flight.
Office of Aviation Medicine Report No. AM 65-28, Fed-
eral Aviation Agency, December 1965.

5. Pearson, R. G., and Byars, G. E.; The Development

and Validation of a Checklist for Measuring Subjective

Fatigue. School of Aviation Medicine, USAF, Report

No. 66-115, 1956.

e

U.S. GOVERNMENT PRINTING OFFICE: 1966 O—211-396



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Ficure 3. Mean plottings of data obtained in Rome (preflight) and in Oklahoma City (return flight).


changes in chest circumference. The chest strap
was fitted to the subject at the beginning of each
assessment period and removed at the end of the
period. Heart rates were recorded from a stand-
ard indicating cardiotachometer (Phipps-Bird,
Model 70-781) at 30-second intervals. Respira-
tory movements were recorded through an appro-
priate matching bridge (Model 270 Plethysmo-
graph, Parks Elect. Lab.) on a millivolt strip-
chart recorder.

4, Blood Pressure. Blood pressure was meas-
ured periodically throughout each assessment
period by standard auscultatory techniques, using
an inflatable arm cuff and indicating sphygmo-
manometer; both systolic and diatolic pressures
were recorded.

5. Reaction Time. The speed of manual re-
sponse to a variety of stimuli and stimulus con-
ditions was measured by means of a Lafayette
Multi-Choice Reaction Timer modified to pre-
clude secondary cues. Responses were elicited in
order by three successive presentations of a single
auditory stimulus, three successive presentations
of a single visual stimulus, six successive and ran-
domly determined presentations of one of three
possible visual stimuli, and finally by one presen-
tation of the single auditory stimulus. Intervals
of presentation were irregular.

6. Decision Time. This was obtained for
each assessment period by subtracting the mean
time of responding to the three presentations of
the single visual stimulus from the mean time of
responding with the correct response to the six
presentations of one of the three different visual
stimuli. This value is taken to represent the aver-
age time required to “decide” which of the three
possible responses was the correct response to be
made.

1. Critical Flicker-Fusion. Three ascending
and three alternating descending thresholds were
determined by an International Applied Science
Laboratory apparatus (FP104 frequency and pro-
gram module and OFC-8 optical unit). In in-
dicating the highest rate at which this type of in-
put can be adequately processed, these thresholds
are generally considered representative of the
state of efficiency of cerebral function.

8. Numerical Ability. This was measured by
a 90-item, 3-minute test requiring the addition of
one- and two-digit numbers in sets of three (RPM
Number Facility—NF—Alternate Forms—1959
edition published by the Hogg Foundation, Uni-

versity of Texas). The score represents a rela-
tively factor-pure measure in speed and accuracy
of simple addition.

9. Subjective Fatigue. The level of subjec-
tive fatigue was measured by means of checklists,
developed by the scale-discrimination method,
which were shown to reflect significantly the effects
of perceptual-motor work and pharmacological
treatment.*

D. Subjects. Four healthy, adult, male volun-
teers were drawn from the professional and tech-
nical staffs of the Civil Aeromedical Research
Institute. During all periods of assessment, pre-
flight, overseas, and postreturn flight, the subjects
were quartered in wards permitting supervision
of activity. Finally, the subjects were instructed
to maintain their daily living habits in accordance
with the local time of the overseas destination
immediately following arrival.

II. Results.

A. Primary Shift. Data obtained during pre-
flight (Oklahoma City) and postflight (Rome)
days of assessment are given in Figure 1. For
each function, plotted values are the means of the
four subjects for each hour for rectal temperature,
for each assessment period for palmar evaporative
water loss, blood pressure, heart rate, and respira-
tory rate, and for each day of assessment for the
psychological functions. Preflight values repre-
sent the pooled means of the four subjects
for the last 2 days of preflight assessment
observed as being least contaminated by novelty or
unfamiliarity.

1. Rectal Temperature. Examination of the
preflight curve of rectal temperature reveals the
periodicity and amplitude of stored heat typically
obtained under normal circumstances. During
the first day in Rome (Day +1), essentially the
same form of curve is seen, suggesting that a com-
plete shift in phase was achieved. It should be
remembered, however, that time of arrival in
Rome was 1280 hours (Rome time), and so it is
most probable that the phase of the period was
still set to Oklahoma City time. On Day +2,
the predicted phase lag is demonstrated. A pre-
cise determination of the number of days required
for the completion of the shift of phase to the
local time of Rome cannot be made owing to the
variability of the subsequent rectal-temperature
curves, which, for Day +8, is most marked. It
does appear though that shift of phase was not
completed prior to Day +6.


PHASE SHIFTS OF THE HUMAN CIRCADIAN SYSTEM
AND PERFORMANCE DEFICIT DURING THE PERIODS OF TRANSITION:

II. West-East Flight

I. Introduction.

As reported,‘ biomedical assessments were made
on human subjects throughout a week prior to jet
flight to Manila, during 8 days of layover in
Manila, and for a week following return to Okla-
homa City. It was found that the lag time of the
circadian phase shift manifested by rectal tem-
perature and heart rate was approximately 4 days
and, by palmar evaporative water loss, approxi-
mately 8 days. In contrast, shift in phase effected
by return to Oklahoma City required only 1 day.
Behavioral integrity was degraded during the pri-
mary period of transition and, to a lesser extent,
during the period of transition occasioned by re-
turn to the environment of origin, but duration
of behavioral impairment was much shorter than
the lag time of physiological phase shifts.

Data to be reported here were obtained from a
subsequent jet flight to Rome, Italy, designed to
reveal differential effects of East-West and West-
East time displacement.

II. Method.

A. Flight. Time of departure (Oklahoma
City) was 1400 hours (CST), total time in transit
15-¥% hours, arrival time (Rome) was 1230 hours
local time, and time displacement was 7 hours.

B. Schedule of Assessment. As in previous
testing, periodic biomedical assessments were
made on alternate days during the week imme-
diately prior to flight, during a 12-day period in
Rome, and during the week following return to
Oklahoma City. Throughout each test day, as-
sessments were repeated at 0700, 1100, 1500, 1900,
and 2300 hours (local time). During each of
these five periods of assessment, several different
psychological functions were sequentially assessed
by standardized procedures. Simultaneously,
measurements were also made of physiological
functions. The time required for such a period
was approximately 25 minutes.

C. Assessments. The following assessments
were made,

1. Rectal Temperature. Internal body tem-
perature was measured by a portable, indicating
bridge circuit, calibrated to a thermistor rectal
probe that was inserted to a depth of 10 cm, worn
continuously throughout each assessment day, and
removed only for bathing or evacuation. During
transitional overseas movements, the rectal probe
was worn from 0600 hours on the day of departure
through 5 successive days, and subsequently for
24-hour periods on alternate days. During the
waking portion of the day, the subject read and
recorded his own temperature to the nearest 0.1°C
at 1-hour intervals; for the remainder of the day,
a technician recorded the sleeping subject’s tem-
perature at the same interval. No untoward con-
sequences, other than minor inconvenience, were
reported by the subjects as a consequence of the
prolonged periods of rectal-probe insertion.

2. Evaporative Water Loss. The method for
quantitatively measuring skin-surface evaporative
water loss has been described earlier.» * For each
assessment period, a small plastic capsule,? sam-
pling from a 1-sq cm skin area, was sealed to the
skin at the center of the left palm. Measurements
of evaporative water loss from this area were made
continuously throughout each assessment period,
indicating both steady-state “basal” levels during
rest and increased evaporative rates during as-
sessment. These data were examined to provide:
(1) measurements of “basal” evaporative water
loss; (2) increases in instantaneous rates related
to matched assessments; and (3) the total amount
of water evaporated during the entire assessment
period and its individual subcomponents.

3. Heart Rate and Respiratory Rate. A
lightweight, plastic and elastic chest strap was im-
provised to house three silver electrodes for heart-
rate measurement and a mercury-in-rubber strain
gage to monitor respiratory rate as a function of



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