After the evening shift, the controllers appar-
ently accomplish complete recovery during the
sleep period, for the excretion of 17-OH corti-
costeroids shows a highly significant decrease;
the catecholamines also decrease significantly.
After the morning shift, however, the 17-OH
corticosteroids decrease only slightly and insig-
nificantly during the rest period indicating that
there are residual stress effects that would be
expected to be carried over into the next work
period.

Urea is one end product of protein breakdown.
ATC work at O'Hare is characterized by a rela-
tively high urea output, indicating a rather high
rate of protein catabolism.

ATC work at O’Hare was characterized by a
general elevation of the end products of metab-
olism. When the controllers at O’Hare were
compared with other groups, upon which the
same urinary variables were measured, the com-
parison showed that O’Hare Tower work was
more stressful than long or difficult flying oper-
ations, prolonged decompression in an altitude
chamber or a 10-hour period in a flight simulator
by inexperienced subjects.

The control subjects responded to their work
with elevated excretion of metabolic end pro-
ducts, also. These biomedical crewmembers were,
obviously, not controlling traffic but were alter-
nating evening and morning shifts every five
days. As the schedule worked out, each crew
got 24 hours off duty after every ten days of
work. When one crew was off for 24 hours, the
other crew worked a “quick turnaround” sched-
ule (morning and evening shift on the same
calendar day). This work schedule was unfa-
miliar to these people and their response to the
first five days of the morning shift was the most
marked of the entire study. Relatively high
values for epinephrine and 17-OH corticosteroids
were obtained, also, in the morning specimens
after evening work, indicating that the entire

10

task was somewhat stressful. Adaptation to the
morning shift work was evident in that there
was a lessening of the physiologic disturbance
with each return to the morning shift; however,
full adaptation was not attained over the six-
week period of the study. When the control
subjects’ values for excretion products were
graphically compared with those of the ATC
personnel, it was evident that the controls’ re-
sponses were, on the whole, quantitatively less
than those of the ATC personnel.

All measurements indicate that the controllers
are generally in a state of sympathetic excitation,
particularly on the evening shift. This state is
probably accounted for by the controllers’ intense
concern for the separation of aircraft. This
concern is most evident on approach and local
control for it is on these positions that the con-
trollers must deal with converging traffic.

This study was carried out in the summer when
good weather (VFR) conditions prevailed most
of the time. It is to be expected that prolonged
bad weather (IFR) conditions, common to the
Great Lakes area in winter, would engender
quantitatively greater responses than are reported
here.

This report deals only with the first of the
three objectives listed in the introduction, ie, a
comparison of physiological responses of con-
trollers on different shifts and at different tower
positions.

For perspective, the ranges of the various
measurements for other populations of subjects
have been included. These are commonly ac-
cepted values and indicate that the data of the
ATC personnel fall generally within these ranges.
This comparison serves to emphasize that these
ATC subjects were normal individuals and that
significant evaluation of their response to ATC.
work can only be made by comparing them quan-
titatively with themselves in different work
situations,


PHYSIOLOGICAL RESPONSES IN AIR TRAFFIC CONTROL PERSONNEL:
O'HARE TOWER

I. Introduction.

The air traffic control (ATC) task at high
density terminals has been assumed to evoke com-
pensatory physiological responses in the con-
trollers that quantitatively exceed those that are
evoked in the general population by less demand-
ing jobs." It is reported that there is a higher
incidence of stress-related symptoms among ATC
personnel than among non-ATC personnel.’ ?*

The Civil Aeromedical Institute was assigned
the task of carrying out a study that would pro-
vide quantitative objective information about
physiological responses in working controllers.
The purposes of the study were (1) to compare
the physiological responses of controllers on dif-
ferent shifts and at different tower positions,
(2) to place the.air traffic control effort in per-
spective with tasks carried out by other popula-
tions of workers and (8) to compare the physio-
logical responses of controllers at several
terminals where there are known to be qualitative
differences in the work situations. Thus, the
present report and the one by Hale, et al.,° are
the results of the first of a planned series of
studies.

II. Methods.

The study was carried out at the O'Hare Air-
port tower between July 15 and August 20, 1968.
‘Twenty-two controllers ranging in age from 25
to 37 volunteered to participate in the study;
thirteen were journeymen, five were trainees and
four were supervisors. Physiological data were
collected from each of the controllers during five
8-hour work periods on the 1600-2400 shift
(evening, heavy-duty shift) and the 0000-0800
shift (morning, light-duty shift). The practice
at O’Hare was for controllers to rotate from one
tower position to another approximately every
two hours. Thus, none of the shift data relate to
one particular job. Not all trainees were checked
out on all positions, however.

Urine collections were made from 20 of the
subjects and from seven of the biomedical crew-
members throughout the study. The schedule of
specimen collection and the results of the urine
analyses are summarized in the Discussion Sec-
tion of this paper and reported in complete form
separately.® #°

Physiological Measurements

a. Heart Rate: The heart rate is perhaps the
most widely used physiological measurement in
studies of this kind.1* The quickening of the
heart beat is virtually instantaneous when a
threatening, alarming or exciting event occurs.
Because of its wide use, a measurement of the
heart rate is valuable in comparing studies of
different populations of people engaged in
various activities. The electrocardiogram (ECG)
was recorded continuously on miniature magnetic
tape recorders throughout every work period
from each subject. The ECG was taken from
active electrodes placed at each end of the
sternum with an indifferent electrode on the right
lateral chest wall. This placement minimized
interference from muscle potentials. The elec-
trodes were a special silver paste dry type with
insulated 36 G silvered copper wires embedded in
them. The details of the electrodes and their ap-
plication to the skin are published separately.’*
The battery operated tape recorders were carried
in a case suspended by a shoulder strap. Each
nickel-cadmium battery and reel of tape lasted
10 hours; thus, recordings could be made con-
tinuously for an entire work period. Capability
existed for recording ECG’s from four con-
trollers, simultaneously.

The recorders operated at a tape speed of
0.125 inches/sec. Playback was accomplished on
a special scanner that operated at a tape speed of
7.5 inches/sec; thus, a 60:1 time advantage was
gained on playback. The scanner output was
electronically coupled to a digital counter that



d. Blood:

(1) Fibrinogen: Figure 2 is a plot of fibrin-
ogen vs. age in 23 college students, 330 Aero-
nautical Center executives and 21 O’Hare ATC
personnel. A general trend is apparent, about
which the ATC fibrinogen concentrations are
graphed. The ATC personnel are apparently
positioned along the trend line in proportion to
their ages.

The normal value for fibrinogen is reported
to be 270 mg/100 ml of plasma.*

(2) Phospholipids: Treatment of the data
was on a group basis rather than on an individual
basis to see whether there was any significant
difference between the ATC personnel as a group
and a previously studied control group and
whether the phospholipid concentrations from
the ATC group correlated with any other of the
groups (Table V, Fig. 3).

The ATC personnel had a total phospholipid
significantly higher than the control and stressed
groups that have been studied, higher even than
Navy pilots exposed to combat in Vietnam. Two
other phospholipids were significantly different
in this population compared to normals; cardio-
lipin was significantly lower and phosphatidyl
glycerol significantly higher than the -normal
population. The distribution of individual phos-
pholipids in the controller population was not
comparable to any of the other stressed groups
that have been studied ; that is, sleep deprivation,
acceleration in a human centrifuge, combat flights,
or schizophrenia.***> Within the ATC popula-
tion there is no statistical difference between the
evening and morning shifts.

Events were noted by the observers such as
fires in flight, malfunctioning landing gear, loss
of power in flight or any other episode that re-

500-5 A EVENING |
© morNine J ATC
= STUDENT
+ EXECUTIVE .
® 400-4 . . : .
co :
E =
. . . .
Zz .
re . .
S Oo; ° : . °
a to wet
2 ao* i ict .
& 300-4 ces tats . :
2 Oo, «(FAL ticitiyi.
ra . a oa soot fe pe
A ° is, el, :
s Bote : aoe . .
s . “8 th. oan
4 8 a& :
a® A ° a .
o AA wee : :
2004 . ro . : .
s .
a
a
T T T T T T T T 1
20 25 30 35 40 45 50 55 60 65
AGE - yrs

Figure 2.—Plot of fibrinogen vs. age for O’Hare controllers, college students and FAA executives. ATC personnel
are positioned in the group according to their ages with no apparent differentiation of shifts.

6


in the plasma is thought to reflect a stimulation
of energy-yielding reactions in all cells of the
body, but particularly in brain cells, whenever
an event occurs that is perceived as threatening.

The quantity of fibrinogen in the plasma has
been shown to increase in response to noxious
stimuli such as electric shocks, the aging process
and illness.14*°*! Fibrinogen levels have been
followed during treatment of patients suffering
from a variety of diseases and the degree of re-
mission was correlated with decrements in fibrin-
ogen concentration.**

At the end of the work period on the fifth day
of each shift, 10 cc of blood was drawn from the
antecubital veins of 19 subjects. Only one speci-
men was obtained from each of three other sub-
jects. The blood was drawn into plastic syringes
which were quickly emptied into centrifuge tubes
containing dried EDTA, an anticoagulant. The
blood was mixed with the anticoagulant by re-
peated gentle inversion. The blood was centri-
fuged, the plasma was drawn off with pipettes
and emptied into glass test tubes. The stoppered
tubes of plasma were immediately placed in re-
frigerated containers and were sent by air within
12 hours to the Civil Aeromedical Institute in
Oklahoma City where the fibrinogen determina-
tions were made.

Fibrinogen was converted to fibrin by reacting
0.2 cc of plasma with thrombin. The fibrin was
then solubilized and determined spectrophoto-
metrically by the method of McKenzie, et al.?*

The remainder of the plasma was frozen and
stored until it was taken by courier to the U.S.
Naval Air Development Center, Johnsville, War-
minster, Pennsylvania, where phospholipid anal-
ysis was carried out. Total phospholipid
components were determined separately on each
controller’s plasma by the method of Dawson®
as used by Polis, et: al.?*?°

Three urine specimens daily during the five-
day observation period were collected by 20 of
the ATC personnel and by seven of the biomedi-
cal crewmembers who served as controls. The
three specimens represented three levels of work-
load. The first part of the evening shift was the
heaviest work period of the day while the last
part of that shift was fairly light. Conversely,
the first part of the morning shift was a light
traffic period and the last part was a heavy duty
period. Pooled urine specimens were thus col-

lected during the first four hours of each shift
(Specimen 1) and during the last four hours of
each shift (Specimen 2). For baseline reference,
a third specimen was collected at the end of the
off-duty sleep period. Obviously, the third
specimen was collected at different times of day
depending on which shift was worked, the per-
sonal preference of the subjects about bedtime
and the duration of sleep.

The ATC personnel each collected urine only
during the five days of study on each shift. The
biomedical crewmembers who alternated five
evening shifts and five morning shifts, collected
three urine specimens daily for the entire period
of the study.

Urine specimens were collected into HCl-
charged screwcap plastic bags that were carried
in insulated attache cases containing a bottle of
frozen coolant. The specimens were adjusted
approximately to pH 2 with HCl and 250 ml
aliquots were bottled, frozen and shipped to the
Applied Physiology Branch of the U.S. Air
Force School of Aerospace Medicine, Brooks
AFB, Texas, where they were analyzed in dupli-
cate for epinephrine, norepinephrine, 17-OH
corticosteroids, sodium, potassium, phosphate,
urea and creatinine,

Ill. Results.

a. Heart Rate: Data relating heart rate to
work at the various positions for the two shifts
are summarized in Table I which shows, for all
positions where sufficient data were collected,
that the busier evening shift gave rise to signifi-
cantly higher heart rates than the morning shift.

Heart rates on the different positions within
shifts are summarized in Tables II and III.
These tables show that on the evening shift, local
and approach control were not different, but that
each of those gave rise to significantly higher
heart rates than did departure control. On the
morning shift, it appears that none of the posi-
tions differed.

The mean heart rate for humans is reported
to be 71 beats per minute with a range of
52-1043

b. Galvanic Skin Response (GSE): The means
of the maximum and minimum resistances for 15
controllers were graphed for a five-day morning
shift and for a five-day evening shift (Fig. 1).



was set to accumulate the count of R-waves of
the ECG for one second when the count was then
electronically dumped into a printer which put
the accumulated count on a paper strip. Be-
cause of the 60:1 time advantage, each second
of playback represented one minute of recording.
The tape-recorded data were thus reduced to a
printed column of one minute heart rates.

Since the heart rate was influenced by physical
exertion unrelated to air traffic control, it was
necessary to exclude from the data such events
as walking up and down stairs, meal breaks, ete.
To that end, and for identification of specific
air traffic control functions, controller-observers
provided commentaries with time identification
on small hand-held tape recorders. These logs
were transcribed and used to exclude inapplicable
heart rate data and to identify specific events.

b. Galvanic Skin Response: The galvanic skin
response (GSR) is a measure of involuntary
nervous system activity. It is considered to be a
sensitive indicator of a person’s involvement in
an activity. It is, for example, commonly used
as a lie detector. The skin electrical resistance,
particularly of the fingers and palms, decreases
when the individual is aroused or excited in any
way.

The tips of the forefinger and index finger of
the left hand were cleaned with alcohol and an
adhesive corn pad with a round hole in it was
placed over each site. The holes in the corn pads
were filled with conductive jelly and cut-to-size
GSR electrodes were positioned in the paste at
the top of the holes. The electrodes were secured
with tape. The electrical resistance between the
fingers was measured by a calibrated bridge cir-
cuit and recorded directly on a strip chart re-
corder. Data were collected from 15 controllers.

Four cables were laid around the outer pe-
riphery of the tower cab counters and dropped
down the stairwell to the first landing where two
strip chart recorders were located. The cables?
cab terminals were arranged so that when a con-
troller changed work positions his GSR leads
could be connected to a nearer cable. In the IFR
room at the base of the tower, a strip chart re-
corder was set up at each departure control posi:
tion. Cables were run to each of the two approach
control and two departure control positions.
With this arrangement of cables and recorders,
it was possible to record from two controllers in

the cab and two controllers in the IFR room,
simultaneously.

c. Other Observations: Blood pressure of the
left brachial artery was taken with an aneroid
manometer pre- and post-shift. The subjects
were in the sitting position with the cuff at the
level of the heart. Systolic pressure was read
at the first and diastolic pressure at the last
Korotkov sound.

Oral temperature was checked with a clinical
thermometer to reveal any fever that might exist.
No controllers were found to be febrile during
the study.

“Resting” heart rates ‘were taken when the
subjects were instrumented by observing and
counting for one minute the electrical deflections
taken from the recorder and displayed on an
oscilloscope. This procedure served primarily to
verify the operational integrity of the electrodes,
leads and recorder through the amplifier stage.
Heart rates thus observed were commonly higher
than the on-duty rates reported in Results because
(1) the controllers were not fully recovered from
the physical exertion of walking from the park-
ing lot to the tower and climbing two flights of
stairs to the briefing room, (2) anticipatory ex-
citement and concern about biomedical proce-
dures, and (3) the on-duty data were treated
during reduction to exclude all periods of physi-
cal activity that would contribute to elevated
heart rates.

Tape recorders were inspected daily for proper
motor and electronic operation. It was not pos-
sible to check for proper recorder operation
while they were actually in use. One problem
involving high-frequency random noise appear-
ing at some point beyond the recorder amplifier
was operationally solved by changing the type
of tape. The problem resulted in considerable
loss of heart rate data before it was corrected.

Blood and Urine

Certain fat-like and protein components of the
blood are considered to increase in proportion to
the intensity of the environmental, psychic or
work stimulus. The pattern and quantity of
phospholipids in blood plasma have been used
as indicators of stress in combat personnel,
mental patients and in people subjected to ac-
celeration in a human centrifuge.?*** The ap-
pearance of increased amounts of phospholipids


The means of the maximum and minimum re-
sistances were derived from the maximum and
minimum resistances recorded each hour for each
subject.

Figure 1A (the morning shift) indicates that
the opportunity to relax increases through the
five-day period. This may be caused by the
adaptation to the change in the sleep pattern or
to the adjustment to the decreased air traffic
activity as compared to traffic of the evening
shift. No trend toward adaptation to the evening
shift is indicated in Figure 1B. The minimum
resistance levels are similar to those shown in
Figure 1A, whereas the maximum resistance
levels are reduced. The maximum and minimum
resistances for both shifts were found to be
statistically different at the 19% level of signifi-
cance,

For comparison with the controllers’ data,
values of the GSR for people in a relaxed en-
vironment range from 300-800 K ohms."

c. Blood Pressure: It has been reported that
ATC personnel exhibit a lower incidence of
hypertension (systolic over 140 or diastolic over

3507

3007

250Pr

200 l

GSR (KQ)

150F

100F

50F A

Oo 1 i 1 i _t
DAY | 2 3 4 5

MORNING SHIFT

Ficure 1—Galvanie skin response on (A) the 5-day morning shift and (B) the 5-day evening shift.
values are the means of the maximum and minimum resistances, respectively, for each subject.

90) in each age group than do non-ATC per-
sonnel; radar operators, however, are reported
to have a higher, though statistically insignifi-
cant, rate of hypertension than non-ATC per-
sonnel.? Table IV shows that the mean values
pre- and post-shift scarcely differ from each
other within shifts or between shifts, nor do the
mean values indicate that the controllers are
hypertensive as a group. Out of 398 determina-
tions of blood pressure, in only four cases were
the above criteria for hypertension met, two
systolic pressures of 143 and diastolic pressures
of 97 and 100.

For reference, blood pressures of a large popu-
lation of men in the 25-40 year age bracket are
reported to range from 92-155 systolic and 54-
101 diastolic.

‘Taste IV, Mean Blood Pressures Within Shifts and
Between Shifts.
Pre-Shift Post-Shift
Evening 117+ 9/7310 116+ 9/7649
Morning 115+10/73+10 115+10/72+8
3507
300F
250F
4 200}
z /
&
® sob
look Ll
A,
50 B 4
° L 1 i L —_
DAY i} 2 3 4 5
EVENING SHIFT
The daily
(A) shows

that the upward trend of maximum resistance continues over the 5-day period. Such a trend is not evident

for (B).



TECHNICAL REPORT STANDARD TITLE PAGE

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-71-2
‘4. Title and Subtitie 5. Report Date

January 1971

©. Performing Organization Code

PHYSIOLOGICAL RESPONSES IN AIR TRAFFIC CONTROL
PERSONNEL: O'HARE TOWER

7. Author’s) 8. Performing Organization Report No.
C. E. Melton, Jr., J. M. McKenzie, B. David Polis,
G. E. Funkhouser, P. F. Iampietro

9. Performing Organization Nome and Address 10. Work Unit No.

FAA Civil Aeromedical Institute; P. 0. Box 25082;

Oklahoma City, Oklahoma 73125 TT. Contract or Grant No.
Aerospace Medical Research Dept.; U. S. Naval Air

Development Center; Johnsville, Warminster, Pa. 13. Type of Report and Period Covered
12. Sponsoring Agency Name and Address

Office of Aviation Medicine OAM Report

Federal Aviation Administration

800 Independence Avenue, S. W. 14. Sponsoring Ageney Code

Washington, D. C. 20590

15. Supplementary Notes

This study was done under Tasks AM-B-69-PHY-34 and AM-B-70-PHY-34.

16. Abstract

Physiological and biochemical measurements were made on 22 air traffic controllers
at O'Hare tower during five days of the heavy traffic evening shift (1600-2400) and
five days of the light traffic morning shift (0000-0800). Pulse rates were higher
on the evening shift than on the morning shift. Converging approaching traffic

was more excitatory than departing diverging traffic on the evening shift; there
was no differential response on the morning shift. Galvanic skin response indicated
that adaptation to the morning shift was incomplete in five days. Fibrinogen levels
in controllers' blood was not elevated above the expected level for their age group.
Controllers had a higher total plasma phospholipid concentration than populations

of normal people, schizophrenics and combat pilots. Phosphatidyl glycerol was
significantly higher in controllers' plasma than in the normal population but less
than in the combat and schizophrenic populations. Findings from urine analyses

that are reported separately by Hale, et al., have been summarized in this report
Urine chemistry shows that catecholamine excretion is related to the number of
aircraft operations. Corticoid excretion rises late in the morning shift and
recovery from morning shift work is incomplete during the off-duty rest period.

17. Key Words 18. Distribution Statement

Availability is unlimited, Document may
be released to the National Technical
Information Service, Springfield,
Virginia 22151, for sale to the public.

Stress, Heart Rate, Galvanic Skin
Reaction, Blood Phospholipids

19. Security Classif. (of this report) 20. Security Classif. (of this page) Ti. No. of Pages | 22. Price
Unclassified Unclassified il $3.00

Form DOT F 1700.7 (e-69)



during the periods of traffic control work were
undoubtedly due to a combination of emotional
and physical factors, the exact proportion being
undeterminable but apparently heavily weighted
toward emotional factors. The data show that.
heart rates recorded during the evening shifts
are significantly higher than those recorded dur-
ing the morning shifts. This finding is to be
expected since the number of operations during
the evening shift sometimes reached 200 per
hour, whereas on the morning shift the number
of operations was commonly less than 25 per
hour. This finding is consistent with Hale’s®
finding that the heavy-duty evening shift is
characterized by adrenomedullary stimulation
and consequently higher urinary excretion of
catecholamines than is the morning shift. The
data were not collected in a way that allowed
heart rates to be correlated with individual op-

erations; however, it is logical to suppose that
each operation constituted an individual stimulus
to which there was a response with a temporal
decay. When operations were close together, de-
cay did not occur and the elevated heart rate was
sustained.

When the heart rate data are examined with
respect to tower position, several interesting cor-
relations appear. First, it is apparent that the
cab positions engender the highest heart rates.
Secondly, approach control gave rise to higher
heart rates than did departure control. Thirdly,
all positions on the evening shift gave rise to
higher heart rates than did the same positions
on the morning shift.

When different positions were compared within
shifts, it was revealed that local control and
approach control were not significantly different

TOTAL PHOSPHOLIPID AND PHOSPHATIDYLGLYCEROL
AS STRESS INDICES IN HUMAN POPULATIONS

TOTAL PHOSPHOLIPID P

*
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3000. 2 & 5 uw
3 3 3-
a E E
o a 2. _
=
2 2000
1000

woven eens DEMARCATION OF SIGNIFICANT DIFFERENCES AT THE
Fieure 3.—Graph of total phospholipid phosphorus and phosphatidyl glycerol for five groups of subjects.

PHOSPHATIDYL GLYCEROL

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=
2
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3
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=

bEMP/L

1% LEVEL

Con-

trollers show a higher titer of all phospholipids than any of the other groups but their phosphatidyl glycerol
level (a more specific and less variable index than total phospholipid) exceeds only those of the normal popu-

lation and simulated combat flight group.


Taste V. Comparison

of Plasma Phospholipids of Air Traffic Controllers and A Normal Population.

uM Phospholipid P/liter % Distribution
Total Phos- | Phosphatidyl | Phosphatidic | Phosphatidyl | Phosphatidyl | Phosphatidie | Phosphatidy!
pholipid | lsthanolamine Acid Glycerol Ethanolamine ‘Acid Glycerol
Air Traffic
Controllers
A. Routine #3042 **50.7 *20.7 *45.0 1.68 0.69 *#1,49
Shifts +84 +20 +£0.7 +2.2 +.07 +.08 £07
N=25
B. Excep- +8272 *62.4 *20.6 *43.4 1.91 0.63 182
tional £104 £36 £15 +26 £10 £04 £07
Situa-
tions
N=15
Normal Popu- 2272, 41.0 14.2 24.7 1,83 0.65 112
lation +84 +25 +9 +20 +.10 +.04 +.09
N=32

*P (t) <.001 when compared to normal population.
**P (t) <.01 when compared to normal population.
A Mean+S.E.

quired special handling by the controller and
where there was an element of hazard. Those
shifts on which the emergencies occurred were
later identified and the data were extracted.

When the phospholipid analyses for individual
controllers in so-called exceptional or emergency
conditions were compared to the data obtained
in routine conditions, there was no significant
difference between the two groups. However,
both groups were significantly different from a
control population.

For perspective, human plasma is reported to
contain between 2225 and 3516 »M of phospho-
lipid phosphorus per liter.?

IV. Discussion.

The physiological response of air traffic con-

trollers to their work is assumed to arise from
their concern for the consequences of their in-
structions, for the physical work that they do is
apparently minimal. The controller’s mental
image of aircraft positions in the airspace for
which he is responsible and his projection of those
positions into the immediate future gives rise to
central nervous system outflow patterns that are
affected by his uncertainties about the accuracy
of his projections. The problem associated with

any assessment of the controller’s physiological
state is how to tap that outflow appropriately so
that meaningful data are collected.

Central nervous system (CNS) efferents inner-
yate somatic, visceral and endocrine structures.
These innervations result in skeletal muscle
activity through the somatic nerves; a modifica-
tion of activity of cardiac muscle or of the smooth
muscle of the vasculature, the digestive tract and
the genito-urinary system by the autonomic
nerves; and glandular secretions resulting from
autonomic activity and from the brain itself. In
this study, attempts were made to tap these three
outflow pathways of the brain by measuring the
effector responses of each.

The heart rate is affected by all three CNS
effluents. Muscular activity, mediated by somatic
motor nervous activity, gives rise to increased
cardiac output which involves increasing both
rate and stroke yolume. Emotional factors may
cause direct sympathetic acceleration or vagal
(parasympathetic) slowing. Catecholamines
from the adrenal medulla and other chromaffin
tissue cause acceleration of the heart. Increases
in heart rate brought on by muscular exertion
unrelated to the control of traffic were removed
from the data. Heart rate changes occurring



‘Taste I. Comparisons Between Morning Shift and Evening Shift.

AVERAGE HEART RATE

Significance Level

Number of ATC Evening Morning +10, .05, .01, or
in Comparison Activity Shift Shift NS (not significant) **
9 Local Control 101.70 82.51 OL
3 Ground Control 100.43 79.93 *
1 Clearance Delivery 90.50 86.00 *
12 Approach Control 90.77 1.23, OL
2 Departure Control 84.88 7483 01

* Data not sufficient to make a statistical test.
** Wilcoxen matched pairs signed rank test.

Taste II. Comparisons* Between Types of Activity During Evening Shift.

Number of ATC Average Average Significance Level
‘in Comparison First Activity Heart Rate Second Activity Heart Rate — .10, .05, .01, or NS***
14 Local Control 94.59 Approach Control 89.24 Ni
14 Local Control 94.37 Departure Control 84.75, OL
7 Approach Control 88.55 Departure Control 84.57 05
4 Ground Control 99.20 Local Control 105.72 *
2 Ground Control 98.60 Departure Control 95.10 *
3 Ground Control 97.56 Approach Control 94.23 +e

* Data not sufficient for comparisons among other activities.
** Data not sufficient to make a statistical test.
*** Wilcoxen matched pairs signed rank test.

‘Taste III. Comparisons* Between Types of Activity During Morning Shift.

Number of ATC Average Average Significance Level
in Comparison First Activity Heart Rate Second Activity Heart Rate .10, .05, .01, or NS***

9 Local Control 81.51 Approach Control 79.51 NS.

9 Local Control 81.61 Departure Control 7789 NS.

il Approach Control 75.95 Departure Control 74.16 NS.

6 Ground Control 79.18 Local Control 83.20 NS.

6 Ground Control T3AT Departure Control 79.28 NS.

4 Ground Control 76.30 Approach Control 80.42 **

5 Clearance Delivery 84.02 Local Control 83.98 owe

3 Clearance Delivery 83.76 Ground Control 83.90 iad

4 Clearance Delivery 83.27 Approach Control 78.82 *

4 Clearance Delivery 85.45 Departure Control 81.22 *

* Data not sufficient for comparisons among other activities.
**Data not sufficient to make a statistical test.
*** Wilcoxen matched pairs signed rank test.




r

NX

ge

°

10.

1.

12,

13.

14.

15.

16.

. Dougherty, J. D.

. Greiner,

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The

30244



AUTHORS
C. E. Melton, Jr., Ph.D., Civil Aeromedical Institute, Federal Aviation Ad-
ministration, Oklahoma City, Oklahoma.

J. M. McKenzie, Ph.D., Civil Aeromedical Institute, Federal Aviation
Administration, Oklahoma City, Oklahoma.

B. David Polis, Ph.D., Aerospace Medical Research Department, U.S. Naval
Air Development Center, Johnsville, Warminster, Pennsylvania.

G. E. Funkhouser, B. A., Civil Aeromedical Institute, Federal Aviation
Administration, Oklahoma City, Oklahoma.

P. F. Iampietro, Ph.D., Civil Aeromedical Institute, Federal Aviation
Administration, Oklahoma City, Oklahoma.

ACKNOWLEDGMENT

The Civil Aeromedical Institute is grateful to the National Aeronautics
and Space Administration, Flight Test Center, Edwards, California, for the
electrocardiographic tape recorders, scanner and associated equipment.





on the evening shift with regard to controllers’
heart rates. However, each of those positions
gave rise to significantly higher heart rates than
did departure control. On the morning shift,
there was no statistically significant difference
between any of the positions.

The heart rate data can be summarized as
follows: (1) The evening shift elicited a greater
response than did the morning shift, (2) cab
positions were more stimulating than radar po-
sitions, (3) approaching traffic evoked a greater
response than did departing traffic.

The skin electrical resistance (GSR) is taken
to represent the level of central nervous system
arousal. It is fairly nonspecific in that any
event that is attention getting, arousing, exciting
or emotional will cause a drop in skin resistance.
In an earlier study on pilots operating an air-
craft simulator, the skin resistance consistently
took an abrupt drop a second or so before the

subject reached to his pocket for a cigarette. The

skin resistance is related to the activity of sweat
glands. The sweat glands of the hands are
activated by sympathetic nerve discharge which,
in turn, is related to the activity of the reticular
formation in the brain stem. The reticular acti-
vating system is the lower brain center that is
responsible for arousal of the higher brain
centers." *?

The GSR data show that the level of arousal,
derived from the minimum resistances, is about
the same on the two shifts. However, the maxi-
mum resistances indicate that there is less sus-
tained stimulation associated with the morning
shift than with the evening shift. Also, the data
show that the maximum resistances continued to
increase over the five day shift, indicating that
adaptation was occurring, but not reaching com-
pletion. There was no indication of adaptation
to the evening shift.

Although the level of circulating fibrinogen
is known to increase following exposure to a
variety of noxious stimuli, no studies of the
effects of workload have been made. It is gen-
erally believed that elevation of the fibrinogen
level is a function of both degree and duration
of the stimulus. Thus, the finding that fibrin-
ogen values of the O’Hare personnel are con-
sistent with those of other personnel of compar-
able age may reflect the observation that the

chronic stimulus of ATC work is below the
threshold of response of the fibrinogen system.

Also, it must be remembered that most of the
data found in medical literature on the subject
are derived from samples taken in the morning
by hospital laboratories. Therefore, the data
presented in this study are subject to the addi-
tional qualification that they may ‘represent a
circadian ebb in fibrinogen level; however such
circadian studies have not been made.

When the controllers’ plasma phospholipids
were compared with those of a control popula-
tion, however, important differences appeared.
Total plasma phospholipid and plasma  phos-
phatidyl glycerol were significantly elevated in
the controllers. The total phospholipid concen-
tration has been associated with sustained action
of injected catecholamines in animals* and may,
in these controllers, be associated with their ele-
vated urinary catecholamine exeretion.®

The complete data derived from biochemical
studies of the urine of ATC personnel and con-
trol subjects will be published separately in the
open literature’ ?? and the reader is urged to
consult those papers for the complete results and
interpretations. However, a summary of those
findings is offered here so that the essentials of
the whole study can be available in one document.

There were many points of statistically sig-
nificant differences in excretion of metabolic
products between equivalent periods of the eve-
ning shift and the morning shift, generally in
the direction of a decrease in excretion of those
products on the morning shift for the first four
hour period and an increase in the last four hour
period. ‘This finding is reflection of the fact
that the first four hour period of the evening
shift is an extremely busy period while the first
four hours of the morning shift is a relatively
quiet time while the last four hours of the morn-
ing shift is a rather busy time at O’Hare when
freighters are bringing goods into Chicago for
the day’s business. The rise in 17-OH corti-
costeroid excretion by the controllers during the
last four hours of the morning shift is note-
worthy in that it indicates that the workload at
the end of that shift is acutely stressful. The
interpretation might be placed upon this finding
that at the end of the mid-shift the controller is
called upon to make an intense effort to meet the
demands of his job.