the subject cannot either hold one of the
four lights matched or effect a new match
for 1 second on one of the stimuli, the
signal is given to the inside observer to
restore the subject’s oxygen supply. The
inside observer may, however, restore OXY-
gen prior to this if he deems it necessary.

Following restoration of oxygen, the
subject completes block 11 and goes im-
mediately on to block 19, After block 12
is completed, the descent starts.

Phase 4. Descent. Subject remains on oxy-
gen until jnside observer claims it safe
to go to ambient air, Descent at 3,000
ft/min.

All of the subjects were active air crewmen:
pilots, navigators, or flight engineers who had had
previous physiological training in the altitude
chamber either by the military or FAA.

TI. Results

Figure 2 presents the result of a subject ex-
to hypoxia at 35,000 feet. ‘Trials are plot-
ted horizontally along the X-axis, while elapsed
time starting from the onset of the seventh cycle
of the experimental run is on the Y-axis. The
lower sloping dashed line represents the subject’s
baseline performance rate. The solid line, rep-
resenting the subject’s performance, manifests his
deterioration in rate of performance as it curves
upward. The lower arrow indicates the point at
which the subject went from 100% oxygen to am-
pient air, while the upper arrow shows return to
100% oxygen.

Time

versus

Ficure 2. Cumulative trial-completion time
trials, subject PU, 35,000 feet.

Figure 8 presents a plot of performance rate
against time off oxygen in tenths of minutes.
Performance over a given period of time is ex-
pressed as @ percentage of baseline or normal work
rate. Thus, for this subject the point plotted at
0.6 minute, indicates that for the 0.2 minute be-
tween 0.4 and 0.6 minute, his performance was
approximately 687% of normal.

EXPERIMENTAL WORK RATE

B07

120

110
NORMAL WORK RATE

100
90
80
70
60
50
40

% OF NORMAL RATE

30
20
10

°

02 04 06 08 10
MINUTES

Froure 38. Performance for 0.2-minute intervals follow-
ing switch to ambient air, subject PU, 35,000 feet.

Figure 4 presents the data for all subjects run
at 35,000 feet. ‘The solid line represents the sub-
ject’s normal performance work rate as 100% effi-
ciency, and the broken line shows the average
experimental-performance work rate. The aver-
age line shows a dip immediately after the subjects
begins on ambient air, which may be attributed
to the distraction of having to shift one’s mode of
breathing. Note that at 0.8 minute the average is
below all three plotted points. ‘Actually, a fourth
point exists, and if plotted, it would appear at 0%
performance, as subject MA was put pack on
oxygen before 0.8 minute elapsed. In like man-
ner, the averages appearing for the points 1.0 and
12 are based on scoring those returned to 100%
oxygen before that time as having 07% rate of
normal performance.

Performance versus time off of 100% oxygen for
all seven subjects at 27,500 feet, is shown in Figure
5, The broken line shows their average. Once
the subject was placed back on oxygens his experi-





Scow complex coordinator.

lem. The swee
ights serves to a

ping red hand followed by the red
ct as an additional motivating

subject to respond with
When all four lights
5 & new problem was
the second series of
ic problem was intro-
ject to determine the
logic aspect was pro-
aining five stimulus
dle lower white light
it indicated the correct
Ww the stimulus light for
green central light was

the matching vesponse light.
were matched simultaneously,
automatically presented. Tn

‘us, when the mid
adrant came on,
response was one light belo
that quadrant. The fifth

applicable to all four quadrants, and, when lit, it
indicated that the correct response was one above
the stimulus light. When both the quadrant white
light and the green light were on, they cancelled
each other and the correct response was a straight
match. Before starting the hypoxia run, all gub-
jects received a minimum of 15 cycles of training
or 875 trials, which brought their performance
down toa reasonably level plateau,

The experimental run consisted of 10 cycles of
performance with interpolated rest periods. Con-
currently, the subject prebreathed 100% oxygen,
and an ear-sinus check to 10,000 feet was made.
The experiment was conducted in a low-pressure
chamber. The temperature inside the chamber re-
mained at 72° F during the experiment, Each sub-
ject was fitted with an air-line crew-member oxy-
gen mask. The oxygen regulator used was an
A-14 diluter demand bressure-breathing type.
All subjects prebreathed for 20 to 25 minutes prior
to the onset of hypoxia. After return to ground
level, an ascent to the experimental altitude was
made at a rate of. 3,000 ft/min,

The experimental Protocol was in four phases as
follows:

Phase 1. Subject prebreathes 100% oxygen
for 20 minutes, Subject: buckles in seat,
Chamber at ground level. Subject per-
forms 6 cycles or 150 trials on coordinator,
in blocks of 50 with I-minute rests be-
tween each cycle,

Phase 2. Ascent to altitude at 3,000 ft/min.
At outset of ascent, subject starts 100
trials with no interpolated rest period un-
til finished with the 100. Still on 100%
oxygen. Ascent consumes 12 minutes,

Phase 3. At 35,000 feet. Most subjects will
have completed ascent series of 100 trials
prior to reaching 35,000 feet, If not,
subject is to continue until he completes
100 ascent series, following which a 1.
minute rest occurs, Subject resumes work
now on cycle 11. After completing ap-
proximately 10 trials of block 11, the in-
side observer takes the subject off oxygen.
The subject has no forewarning of this
and is unable to observe the observer clog-
ing the oxygen valve, The subject con-
tinues to work as long as possible. The
outside coordinator experimenter at this
point monitors the event recorder, and
when a 5-second period elapses in which


130 © PH OSE

° PU © MA
t2oF ° ® Average
Hof ° °

NORMAL
100 > OR
w 8 * WORK RATE
& 90
«
4 80 °
z
Zz 70F ° ° Ne
2 sof ar
<2 °
S sof ° #\
® aol
30f
20F
tok
°
02 0.4 0.6 0.8 Oe 14
MINUTES.
Fraure 4. Individual and average performance rates for
0.2-minute intervals, 35,000 feet,
150 CPU wR
Ace AM
HSE Average
130 ae?
120 ae
°
oh gg Boe °/ N
# \ NORMAL
é 100 " WORK RATE
a 20
Fe
z 8
2 10
S 60
® 50
40)
30
20 \
\
\

10 a\ ny

° toe oy yy a1

02 04 06 08 10 12 14 16 18 20 22 24 26 28 30 32 34
MINUTES

Figure 5, Individual and average performance rates for
0.2-minute intervals, 27,500 feet,

mental work rate was considered to be zero. It is
assumed that had he not been returned to oxygen,
he would not have completed another trial. The
two solid lines represent the performance rates of
the two extreme subjects.

A smoothing of the data by use of moving aver-
ages for the 35,000- and 97, »500-foot groups appears
in Figure 6. The use of moving averages tends
to even out irregularities in the data and to make
underlying trends more prominent. On the
35,000-foot data, averaging the values for three

x 35,000'
® 27,500"
#
ge
=
ye
as
ge
ae
us
3
ce
x
*s
®

2 4 6 8 10 12 14 16 18 20 22 24 26 28 3.0
MINUTES

Ficure 6, Moving performance-rate averages for 0,2-
minute intervals, 27,500 and 35,000 feet,

Successive time intervals yielded the average for
the midpoint of the three intervals. The 27,500-
foot curve covered far more intervals; therefore,
the moving average was based on five intervals.

The straight line Plotted for the 27,500-foot
curve appears to disregard the tail of the curve at
the right; however, the tail is caused by two sub-
jects having prolonged performance time. After
2.2 minutes, the other five have been returned to
oxygen.

The line for the 35,000-foot data shows a much
steeper descent, indicating a more rapid decay in
performance. These data are based on relatively
few subjects but indicate that this approach yields
data not only consistent with prior work but also
gives a more accurate depiction of performance
deterioration. Rather than having a single value
for an altitude, performance capability is ex-
pressed at the rate at which deterioration occurs.

proximately 10% in rate of performance for each
0.1 minute (6 seconds) of time. At 27,500 feet,
this value is about 5% for each 0.7 minute of time.

IV. Discussion and Conclusion

This method of reporting deterioration or decay
of work rate Presents a more accurate means of
associating task performance with degrees of hy-
poxia. This approach offers the possibility of
supplanting the concept of time of useful con-
sciousness, which ig recognized as being an arbi-
trary all-or-none depiction of Operator capabil-
ity. Rather than being concerned with TUC, an


AM 66-15

HYPOXIA AND PERFORMANCE DECREMENT

William F. O’Connor, Ph. D.
Jim Scow, M.D.
George Pendergrass, Capt., USAF

Approved by Released by

J. Rosurt Diuiz, M.D. Pp. V. Srecet, M.D.
Cuter, Crvit AEROMEDICAL Frpprat Air SURGEON
INSTITUTE

May 1966

FEDERAL AVIATION AGENCY
Office of Aviation Medicine



operational definition is proposed wherein operator
capability is assessed by means of changes from
baseline performance rate.

The curves representing changes in rate of per-
formance found for the two experimental altitudes
manifest a correspondence to blood-oxygen satura-
tion found for these altitudes. Additionally, this
form is in accord with equations * that reflect the
rate of oxygen transfer for a given pressure
altitude.

The present study can at best be regarded as
a preliminary one, exploring a means of quantify-
ing performance deterioration as & function of
hypoxia. The performance tasks were not identi-

cal for the two experimental altitudes, the logic
task used at 27,500 feet being more difficult. The
data suggest that quantified indexes of operator
capability follow the plood-oxygen-saturation
eurves—a correlation. that is severely attenuated
when employing the dichotomous TUC concept.

Tt is felt that further investigation utilizing this
approach, should be undertaken to explore the
quantifiable relationships between hypoxia at
various pressure altitudes and degradation of op-
erator performance. One immediate pedagogical
value of such information would lie jn demonstrat-
ing to airmen the progressive nature of hypoxia
degradation.

REFERENCES

1, Wessrer, A. P., and Reynowps, 0. B.: Time of con-
sciousness during exposure to various pressure alti-
tudes. U.S. Navy BuMed Research Project X 716, 7
‘August 1946.

2, Van Lise, B. J. and Srrckney, J. C. Hypoxia.: Chi-
cago: ‘University of Chicago Press, 1963.

3. HorrMan, C. E., CrarK, R. T., and BRowN, B. B., IR:
Blood oxygen saturations and durations of conscious-
ness in anoxia at nigh altitudes. Amer. J. Physiol.
145 ; 685-692, 1946.

Us, GOVERNMENT PRINTING OFFICE: 1966, O-—219-810



Qualified requestors ma;

Center. ‘The general pu

y obtain Aviation Medical Reports from Defense Documentation
blic may purchase from Clearinghouse for Federal Scientific and

Technical Information, U.S, Dept. of Commerce, Springfield, Va. 22151


Ke Jo4
.

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BIOLOGY
LIBRARY

HYPOXIA AND PERFORMANCE DECREMENT

I. Introduction
In the study of hypoxia, the concept of “time
of useful consciousness” (TUC) has been used to
describe that: period of time during which useful
or purposeful acts can still be performed. Fora
given altitude, the TUC is stated as a single figure
or interim of a normal range. Accurate estima-
tion of TUC values are still somewhat confounded
by the fact that they are dependent upon how @
given experimenter has defined useful behavior.
‘Van Liere and Stickney * state:
Most of the tests employed have been.
of an extremely simple nature, such as
writing or simple card-sorting. It seems
to the authors that the more challenging
tests should be used, for example, prob-
Jems in mental arithmetic (p. 311).
A simple task that is highly overlearned, such as
writing one’s name, will tend to give longer TUC
values than. more-complex, less-overlearned tasks.
As a further consideration, the concept: of TUC
necessarily implies that a qualitative judgment
be made as to the point in the task at which the
subject’s performance is no longer useful or pur-
poseful. Though this arbitrary point can be pre-
designated before experimentation, its existence
introduces further ambiguity. It is well recog-
nized that performance in the hypoxic state does
not suddenly change from normal funtioning to
uselessness, but rather that there exists a progres-
sive performance deterioration, perhaps reflecting
the arterial-oxygen saturation’ In Hoffman’s
study, however, although they are presented quan-
titive curves reflecting the lowering of arterial-
plood-oxygen saturation as a function of exposure
to a given altitude, there is no comparable fune-
tion representing decay in performance. A
simple card-sorting task was used and perform-
‘ance was measured in terms of time to first sort-
ing error. The time preceding this point is ac-
cepted as time of useful consciousness, although
there may be considerable fall-off in operator ca-
pability before making this simple error. In at-
tempting to set a TUC value, one is actually decid-

ing at what point along this deterioration curve
performance is no longer useful, the decision being
reflected in the task and measure chosen.

‘The present study js aimed at replacing the con-
cept of TUC with a less-ambiguous and a more-
descriptive concept. Tt is proposed that the de-
terioration in rate of operator performance be
utilized to describe the effects of hypoxia. Per-
formance rate is defined as the ratio of task units
completed in unit time under hypoxic conditions
over task unit completed per unit time under non-
hypoxic conditions. The resultant, an index
value, is a metric, which would permit compari-
sons of different tasks’ sensitivity to hypoxic con-
ditions. This performance rate metric would
also permit charting operator performance as &
function of time exposed to hypoxic conditions.
Tt would therefore follow that performance rate
should show more rapid rates of decrement as the
pressure altitude rises.

Il. Procedure

The above conceptualization of the problem re-
quires an experimental-performance procedure
that will yield continuous measurement of per-
formance comparable in complexity to that of the
aircrew’s task. The performance task was pro-
vided by @ serial-reaction complex coordinator
(Figure 1), which was originally designed as a
modification of the Mashburn. The apparatus
consists of four controls, one for each extremity.
The subject’s display js a panel containing a total
of 45 lights, 20 stimulus lights and 20 response
lights, plus 5 additional individually placed stim-
ulus lights. Each quadrant of stimulus lights is
controlled by one of the four controllers. Below
these lights is an interval timer that can be preset
any time up to 15 seconds. It resets when each
problem is successfully completed. Té the subject
does not complete the problem in the preset time,
there are two red lights on the controller forward
of the hand controls that are lighted and. remain on
until the subject successfully completes the prob-