Fo

10.

11.

12.

13.

14.

15.

REFERENCES

Abraham, S., C. L. Johnson, and M. F. Najjar: Weight by Height and Age for
Adults 18-74 Years, VITAL AND HEALTH STATISTICS, Series 11, No. 208, 1979.

Balke, B., C. E. Melton, and C. Blake: Physiological Stress and Fatigue in
Aerial Missions for the Control of Forest Fires, AEROSP. MED., 37:221-227, 1966.

Blackburn, H., H. L. Taylor, H. Okamoto, P. L. Mitchell, P. M. Rautaharju, and
A. C. Kerkhof: Standardization of the Exercise Electrocardiogram: A Systematic
Comparison of Chest Lead Configurations Employed for Monitoring During Exercise.
In Physical Activity and the Heart, M. J. Karvonen and H. Barry (Eds.),
Springfield, Illinois, A. H. Thomas, pp. 101-134, 1966.

Consolazio, C. F., L. 0. Matoush, H. L. Johnson, R. A. Nelson, and
H. J. Krzywicki: Metabolic Aspects of Acute Starvation in Normal Humans
(10 Days), AM. JOUR. CLIN. NUTR., 20:672-683, 1967.

Consolazio, C. F., R. A. Nelson, H. L. Johnson, L. 0. Matoush, H. J. Krzywicki,
and G. J. Isaac: Metabolic Aspects of Acute Starvation in Normal Humans:

Performance and Cardiovascular Evaluation, AM. JOUR. CLIN. NUTR., 20:684-693,
1967.

Dawber, T. R., F. E. Moore, and G. V. Mann: Coronary Heart Disease in the
Framingham Study, J. PUB. HEALTH, 47:4, 1967.

Dill, D. B., and D. L. Costill: Calculation of Percentage Changes in Volumes
of Blood, Plasma, and Red Cells in Dehydration, JOUR. APPL. PHYSIOL., 37:247-
248, 1974,

Federal Aviation Administration: AEROMEDICAL CERTIFICATION STATISTICAL
HANDBOOK, 1978.

Foux, A., R. Seliktar, and A. Valero: Effects of Lower Body Negative Pressure
(LBNP) on the Distribution of Body Fluids, JOUR. APPL. PHYSIOL., 41:719-726,
1976.

Greenleaf, J. E., J. S. Bosco, and M. Matter, Jr.: Orthostatic Tolerance in
Dehydrated, Heat-Acclimatized Men Following Exercise in the Heat, AEROSP. MED.,
45:491-497, 1974.

Hannon, B. M., and T. J. Lohman: The Energy Cost of Overweight in the United
States, AM. JOUR. PUB. HEALTH, 68:765-767, 1978.

Hartzell, W. G., and P. D. Newberry: Effect of Fasting on Tolerance to
Moderate Hypoxia, AEROSP. MED., 43:821-826, 1972.

Heistad, D. D., and R. C. Wheeler: Effect of Acute Hypoxia on Vascular
Responses in Man, JOUR. CLIN. INVEST., 49:1252-1265, 1970.

Krutz, R. W., Jr., S. A. Rositano, and R. E. Mancini: Comparison of
Techniques for Measuring +Gz Tolerance in Man, JOUR. APPL. PHYSIOL., 38:
1143-1145, 1975.

Lategola, M. T., and C. C. Trent: Lower Body Negative Pressure Box for +Gz
Simulation in the Upright Seated Position, AVIAT., SPACE, & ENVIRON. MED.,
50:1182-1184, 1979.

19


and corresponding nonfasting values for all measured parameters (Tables IX
and X). The moderately low workload used approximated estimates of the
average maximum workload encountered in general aviation flying (2).

Tolerance to LBNP (+2Gz). The effects of various magnitudes and dura-
tions of LBNP on human physiological functions have been reviewed compre-
hensively (29). When healthy young men are subjected to an LBNP of -40 torr,
about 0.5-0.6 L of blood are shifted from the central blood volume by the
pooling of blood in the lower half of the body. The acute loss of central
blood volume gives rise to a complex barrage of reflexes that attempt to
compensate for this loss and ensure an adequate continued perfusion of the
brain (29). Vasoconstriction and increased HR are the two major reflections
of this reflex defense against loss of consciousness (29). Symptomatically,
the temporary adequacy of defense mechanisms is reflected by the behavior
of initial symptoms, which either disappear or stabilize at very low levels
of intensity. In extended durations of LBNP at -40 torr or greater, the
reflex defenses eventually collapse, and syncope rapidly ensues (29). The
main reason for eventual collapse is that, in addition to the pooling caused
by LBNP, there also occurs a substantial time-dependent extravasation of
plasma from the intravascular compartment (16). The syncopal response has
been arbitrarily divided into two phases (20). Phase I (presyncope) is
characterized by physiologic instability in which marked phasic variations
occur in arterial blood pressure, while the mean pressure is slowly falling
and HR continues to rise. Phase II (syncope) is characterized by a precipi-
tous fall in both arterial pressure and HR leading rapidly to syncope (29).
Phase I is characterized by the appearance and intensification of symptoms
such as lightheadedness, dizziness, visual blurring, and pallor. Phase II -
is best characterized by the additional appearance and very rapid intensifi-
cation of nausea and visual grayout, tunneling, and blackout (29). When
healthy, nonfasted normally hydrated men are subjected to an LBNP of -40
torr at GL, the average time to the first appearance of presyncopal symptoms
is 10-30 min (9,21,30).

One of our 11 subjects adequately tolerated the LBNP equivalent of +2Gz
for 2 min at altitude in the nonfasting condition of both the control experi-
ment and the preexperimental orientation session, but was incapacitated dur-
ing the same LBNP test at altitude after the 24-h fast. In order of appearance
and increasing intensity, the subject's symptoms were lightheadedness, visual
graying, and visual tunneling. Because of his motivation to successfully
complete the test, the subject withheld the hand signal for subjective dis-
tress until very nearly the end of the second min of LBNP. When the LBNP was
terminated, the subject's face was pale and sweaty. Supplemental oxygen was
administered immediately, and he recovered facial color and lucidity within
30 s. At the time of signaled distress, the recorded data revealed that: (i)
the HR had peaked at 108 bpm, and was starting to fall precipitously; (ii) the
BP had decreased markedly with a barely visible systolic signal at 52 torr;
and, (iii) the pulsatile TAFV signal was barely discernible, and very close
to zero. The HR, TAFV, and BP recovered in parallel with subjective recovery.
The subject realized that he had "blacked out." From these data it is clear
that, had the subject been piloting an airplane during an equivalent +Gz
maneuver, he would not have been in control of the airplane during this
incapacitation.

13



TABLE II. Schedule of Experimental Protocol

Day 1 Day 2
Time Activity Time Activity
0745 | Report in fasted overnight 0700 | Arise
Urine void Ablutions
Body weight ; Dress
Blood sample 0745 | Urine void
0800 | Breakfast Body weight
1300 } Lunch or Fast Blood sample
1800 } Dinner or Fast 0800 } Breakfast or Fast
2300 | Bedtime 0830 | Sensor placements
0930 | LBNP seal check
0940-0950 | GL resting measurements
0950-1000 | Altitude ascent
1000-1009 Ear oximetry
1010-1025 | 1st math test
1030-1045 | 2nd math test
1050-1100 | Resting measurements
1105-1120 | 3rd math test
1125-1140 | 4th math test
1148-1200 | LBNP procedure
1200-1210 | Altitude descent
1215-1234 | Ergometry procedure
1235-1240 | Sensor removal
1240 | Urine void
Body weight
1245 | Release



16.

17.

18.

19.

20.

21.

22.

23.

24.

25.

26.

27.

28.

29.

30.

Luft, U. C., L. G. Myhre, J. A. Loepky, and M. D. Venters: Specialized
Physiological Studies in Support of Manned Space Flight, Annual Research
Report, NASA, Contract: NAS 9-14472, Houston, Texas, 1976.

McFarland, R. A.: Human Factors in Air Transportation, McGraw-Hill,
New York, p. 159, 1953.

Merimee, T. J., and J. E. Tyson: Stabilization of Plasma Glucose During
Fasting, NEW ENG. JOUR. MED., 291:1275-1278, 1974.

Miale, J. B.: Laboratory Medicine ~ Hematology, Mosby Company, St. Louis,
pp. 656-657, 1958.

Murray, R. H., J. Krog, L. D. Carlson, and J. A. Bowers: Cumulative Effects
of Venesection and Lower Body Negative Pressure, AEROSP. MED., 38:243-247,
1967.

Musgrave, F. S., F. W. Zechman, and R. C. Mains: Comparison of the Effects
of 70° Tilt and Several Levels of Lower Body Negative Pressure on Heart
Rate and Blood Pressure in Man, AEROSP. MED., 42:1065-1069, 1971.

Myhre, L. G., U. C. Luft, and M. D. Venters: Responses of Athletes and Non-
Athletes to Lower Body Negative Pressure and Acute Dehydration, MED. AND
SCIENCE IN SPORTS, 8:53-54, 1976.

Saltin, B.: Aerobic and Anaerobic Work Capacity After Dehydration, JOUR.
APPL. PHYSIOL., 19:1114-1118, 1964.

Saunders, N. A., A. C. P. Powles, and A. S. Rebuck: Ear Oximetry: Accuracy
and Practicability in the Assessment of Arterial Oxygenation, AM. REV. RESP.
DIS., 113:745-749, 1976.

Slein, M. W.: In H. V. Bermeyer: Methods of Enzymatic Analysis, Verlag
Chemie, Weinheim, Germany (1965) » and Academic Press, New York and London,
p. 117.

Snedecor, G. W.: Statistical Methods, Iowa College Press, Ames, Towa, 4th
Ed., p. 54-88, 1956.

Stegemann, J.: Beziehungen Zwischen Trainingzustand und Orthostasetoleranz,
CARDIOL., 61(Suppl. 1):255-256, 1976.

Stevens, P. M., and L. E. Lamb: Effects of Lower Body Negative Pressure
on the Cardiovascular System, AM. JOUR. CARDIOL., 16:506-515, 1965.

Wolthuis, R. A., S. A. Bergman, and A. E. Nicogossian: Physiological Effects
of Locally Applied Reduced Pressure in Man, PHYSIOL. REVS., 54:566, 595, 1974.

Wolthuis, R. A., G. W. Hoffler, and R. L. Johnson: Lower Body Negative
Pressure as an Assay Technique for Orthostatic Tolerance: 1. The Individual
Response to a Constant Level (-40 mm Hg) of LBNP, AEROSP. MED., 41:29-35,
1970.

20


because of the interindividual and intraindividual variability in the ad
libitum amount of its intake. As deduced from body weight data, the rate

of water loss during the 4-h testing period after 24 h of fasting was approx-
imately twice the corresponding rate under the nonfasting condition. Two of
the 4 h of the testing period were spent at an altitude of 3,810 m. Caf-
feine intake immediately prior to or during flight at substantial altitudes
after a 24-h fast could possibly synergize diuretic water losses dispropor-
tionately, and thereby decrease tolerance to applied +Gz. However, since
this facet was not specifically tested in this study, the possibility of
such an adverse effect must remain moot.

This study was confined to subjects who were substantially overweight,
because overweight people are more apt to go on a crash diet than people of
normal weight. In the context that young heaithy men are normally able to
withstand 10-30 min of -40 torr LBNP (+2Gz) before the first appearance of
presyncopal symptoms (9,21,30), three of our subjects manifested a decreased
tolerance to 2 min of ~40 torr LBNP. However, im.the context of ordinary
general aviation flying, a-+2Gz maneuver (e.g., a 60° bank/turn) is not a
common occurrence, and a 2-min sustained duration for such a maneuver would
be even less probable. A 2-min duration for our LBNP test was chosen as an
arbitrary, but reasonable, test of the reserve capacity for +Gz tolerance.
Our finding of some decreased tolerance to +2Gz in three of the subjects may
have some relevance to general aviation pilots who engage in crop dusting or
aerial acrobatics. The possible exposure to +2Gz is probably greater in
these two types of flying. Because Luft and coworkers (16) have shown that,
besides dehydration, blood and plasma volume decreases are also a function
of LBNP duration, the multiple successive +Gz exposures of crop dusting and
aerial acrobatics may have a cumulative decremental effect on +Gz tolerance.
If either of these two activities are combined with relatively high environ-—
mental temperatures and/or fasting, the +Gz tolerance could decrease further.
To our knowledge, the effect of the combination of fasting and heat exposure
on the +Gz tolerance of pilots engaged in crop dusting or aerial acrobatics
has not been studied. Our current findings indicate that pilots engaged in
both of these types of flying would be prudent to avoid acute dehydrations
of all types.

Luft and coworkers (16) have shown that even men of normal weight mani-
fest decreased LBNP tolerance as a result of work-dehydration decrements in
blood and plasma volumes. The two groups of healthy men of normal weight
studied by these investigators (16) consisted of sedentary nonrunners and
active long-distance runners. Although the LBNP tolerance of the five sed-
entary nonrunners was reduced after their plasma volumes had been decreased,
they were still able to tolerate at least 2 min of -40 torr of LBNP. After
a similar bout of work dehydration, two of the five runners tested were
unable to tolerate 2's min of -30 torr. Even in the normally hydrated state,
the runners’ average LBNP tolerance was 58 percent less than that of the non-
runners (16). One of the physiological adaptations to long-distance running
is an increase in circulating blood volume. Unfortunately, because of a
concomitant increase in circulatory pooling capacity, and a concomitant
decrease in circulatory baroceptor sensitivity, the fully adapted normally
hydrated runner is less tolerant than the normally hydrated nonrunner to

17


TABLE VY.

PP and

% A PP
PP (mm Hg) Alt. 2y Alt. 3. +2Gz
GL Ait. 2 Ale. 3 422 Gi 100 Gk 100 area 100
—===

x 49.6 46.1 49.5 | 38.0 92.7 100.8 77.3
Fast

SE 3.2 3.4 3.9 3.0 3.2 6.1 3.5

xX 57.1 56.2 53.2] 45.2 98.5 93.1 85.0
Nonfast

SE 2.0 2.9 3.6 3.8 3.4 5.4 3.8

% A AP
AP (mm Hg) Alt. 2 Alt. 3 +262
GL Alt. 2 Ale. 3 4262 cp * 100 GX 100 aie, 3X 100

_ -

xX 85.9 84.8 82.6} 75.5 99.0 96.3 91.0
Fast

SE 2.4 2.2 2.5 3.7 1.9 2.0 2.2

x 85.7 86.6 85.9 | 80.2 101.0 100.2 93.5
Nonfast

SE 1.7 1.9 2.6 2.9 0.7 1.7 2.9

X = Mean E = Standard error of the mean A = Change

PP = Pulse pressure AP = Mean arterial pressure, calculated
as the value of DBP + 1/3 PP
GL = Ground level altitude (390 m MSL)
Alt. = Hypobaric chamber altitude of 3,810 m MSL
Alt. 2 = Ten-min resting period at 50-60 min of the first hour
at altitude
Alt. 3 = Ten-min resting period at 48-58 min of the second hour

at altitude immediately preceding the simulated +2Gz test
Two-min period of -40 mm Hg LBNP at 58-60 min of the second
hour at altitude

+262


2 min of LBNP at altitude without loss of useful consciousness; and, (iii)
easily tolerated pedal ergometry.

One of the subjects experienced syncope near the end of the LBNP test
after 24 h of fasting, but was adequately tolerant to the same test in the
nonfasting condition of both the control experiment and the preexperimental
orientation session. The data from the other 10 subjects were pooled and
analyzed statistically (26).

These 10 subjects lost an average of 1.2 kg of body weight in 24 h of
fasting and gained an average of 0.4 kg in the 24 h of nonfasting. The dif-
ference between these two average weight changes was statistically signifi-
cant (p = 0.001). During the next 4 h of the experiment session, an additional
average weight loss of 0.4 kg occurred in the fasted subjects and a corres—
ponding average weight loss of only 0.2 kg in the same subjects in the non-
fasting control experiment. The difference between these two additional weight
losses was also statistically significant (p = 0.018).

The blood glucose, hemoglobin, hematocrit, blood volume, and plasma volume
data are summarized in Table III. The decrease in blood glucose associated
with the 24-h fast was about 5 percent, and was not statistically significant
(p > 0.05) when compared to the nonfasting condition. The blood glucose was
assessed in this study to rule out the unlikely but possible occurrence of
frank levels of hypoglycemia (18).

Although not statistically analyzed, the simple math testing at altitude
revealed that fasting had no apparent adverse effect on this type of function.

DISCUSSION

In the nonfasting control condition, statistically significant physiological
displacements (Tables IV-X) were caused by the altitude, ergometry and LBNP
tests, per se. Although statistically significant physiological displacements
occurred, these tests were adequately tolerated without loss of useful conscious-
ness. As stated previously, intolerance to any of these three tests during the
orientation session disqualified the subject from further participation.

Altitude Tolerance. The 2 h of altitude exposure was adequately tolerated
in the fasting condition as reflected by the sustained presence of useful con-
sciousness (math test capability), and by the absence of statistically signifi-
cant differences between the fasting and corresponding nonfasting mean values
for all measured parameters (Tables IV-VIII). The fasting mean values for Hb04
at the end of the first and second h at altitude were 85.1 and 86.5 percent,
and were essentially equivalent to those of the nonfasting condition. An Hb09
value of 85 percent is regarded as being fully compensatory for the hypoxia of
a 3,810 m altitude (17). The absence of any adverse effect on the performance
of simple math is consistent with the HbQ) data.

Fatigue Tolerance. The 6 min of 50 W pedal ergometry was adequately
tolerated under the fasting condition as reflected by the ease of accomplishment
and by the absence of statistically significant differences between the fasting


half in the second experiment session. The data were pooled and statistically
compared (26) on the basis of fasting versus nonfasting conditions. Statis—
tical significance was based on a probability value of p <_ 0.05 (26).

Specific measurements made at altitude consisted of: (i) HR using a
single-lead ECG; (11) blood pressure (BP) using automatic auscultative sphyg-
momanometry 3; (iii) Hb02 using an ear oximeter (24); (iv) pulmonary ventilation
(Vg), respiratory frequency (f), and tidal volume (V7) using pneumotachometry
of expired air; and (v) temporal artery blood flow velocity (TAFV) using a
directional Doppler device (14). Oxygen uptake (¥07) was also measured during
pedal ergometry by analysis of quantitatively collected expired air. Gas
volume data were normalized for differences in body size and expressed as
volume per kg of body weight. The CMs single lead (3) was used to monitor
ECG function. The electrical signal from this ECG lead was fed simultaneously
to: (i) an oscilloscope for visual monitoring of the ECG for ischemia and/or
arrhythmia; (ii) a cardiotachometer for continuous indication of HR; and, (iii)
a standard ECG recorder for periodic recording. Also monitored were the digi-
tal readout of the Hb02 for any indication of hypoxemia; and the pulsatile sig-
nal of the TAFV for any flow-reversal indication of approaching syncope (14).
At altitude, criteria for immediate termination of any experiment consisted
of strong subjective symptoms of impending syncope (lightheadedness, nausea,
and visual grayout, tunneling or blackout) accompanied by sustained hypo-
tension and bradycardia, electrocardiographic evidence of ischemia and/or
arrhythmia, TAFV reversal for at least 5 s and falling values of Hb09 below
80 percent.

Because each subject used a valve mouthpiece during two ventilation
measurements at altitude, three simple hand signals were taught to each one
to communicate that "everything is OK," "subjective distress is present,"
or "stop the test." The same researcher remained in the hypobaric chamber
with the subject during each experiment. Besides continuous direct observa-
tion of the subject, he was often asked if everything was OK. Each subject
was given the unconditional option of stopping the experiment at any time.

A staff physician, a positive-pressure mask source of 100 percent oxygen,
and other emergency resuscitation equipment were always available on a
standby basis.

Mainly to counteract the boredom of quiet sitting, a simple math test
was administered twice during each of the 2 h at altitude. The temperature
and relative humidity ranges in the hypobaric chamber for all experiments
were 21.0°-23.0°C and 20.0-26.0 percent, respectively.

Altitude tolerance was assessed mainly on the basis of maintaining
adequate Hb07 levels. Fatigue tolerance was assessed mainly on the basis
of quantitative shifts in cardiovascular and respiratory functions during
the 50 W pedal ergometry load. The +Gz tolerance was assessed mainly on
the basis of maintaining useful consciousness during the LBNP test.

RESULTS

In both the fasting and nonfasting experiments, 10 of the 11 subjects:
(i) maintained an adequate HbO during altitude exposure; (ii) tolerated


applied +Gz (16,27). When such a runner incurs a plasma volume decrement,
his +Gz tolerance decreases further, and to a disproportionately greater
degree than that of the nonrunner (16,27). Neither the nonrunner nor the
runner of normal weight is apt to manifest plasma volume decrements due

to crash dieting, because neither one is apt to go on such a diet. Because
jogging and long-distance running have become so popular, the number of
such runners in the general aviation population may have also increased
proportionately. Because the normally hydrated runner, who may also be a
general aviation pilot, already possesses a decreased LBNP tolerance, acute
decreases in plasma volume caused by any means may potentially decrease +Gz
tolerance during flight. Regarding this potential vulnerability, two gen-
erating conditions, which may merit. further research investigation are:

(1) an uncompensated dehydration caused by a prolonged running session; and
(4i) an overnight fast. Because the two main studies (16,27) revealing the
disproportionate +Gz intolerance in runners were done at ground level alti-
tudes, the +6z tolerance may decrease further in the pilot/runner when
tested at altitude. Such studies are currently under consideration.

SUMMARY

After 24 h of either fasting or nonfasting, 10 out of 11 subjects:
(i) maintained an adequate Hb0) during altitude exposure; (ii) tolerated
2 min of LBNP at altitude without loss of consciousness; and (iii) easily
tolerated pedal ergometry. One subject was incapacitated (syncope) during
the LBNP testing after fasting, but was fully tolerant to the same test in
the nonfasting condition. Tolerance to infrequent less-than-+2Gz maneuvers
encountered in ordinary general aviation flying would probably be unaf-
fected by a 24-h fast. However, it appears reasonable to recommend that
all general aviaton pilots (especially those engaged in crop dusting and
aerial acrobatics) be informed through educational channels regarding the
advisability of avoiding: (i) prolonged single flight maneuvers (e.g., a
steep turn or a sharp pullup) in excess of +2Gz; or (ii) multiple frequent
repetitions of maneuvers approximating +2Gz, immediately after a total food
fast of 24 h or more.

18


cea

TABLE IV. SBP and DBP
% A SBP
SBP (mm Hg) Alt. 2 Alt. 3y 499 +2Gz_x 400
Gl Alt. 2 Alt. 3 42Gz Ge 100 Ge 100 aie.
+
xX 119.0 115.6 115.6 100.8 97.2 97.2 87.2
Fast
SE 2.6 2.8 3.3 3.7 1.2 2.0 2.2
x 123.8 124.1 121.3 110.3 100.2 97.9 91.0
Nonfast
SE 0.9 1.2 1.4 1.9 1.0 1.4 2.1
& 4 DBP
DBP (um Hg) Alt. 2y i199 Alt. 3. +262 _y 100
GL Alt. 2 Alt. 3 4262 GR 100 geek 100 ate
x 69.4 69.5 66.1 62.8 100.8 95.7 94.4
Fast
SE 3.0 2.6 3.0 4.1 3.1 3.3 2.5
xX 66.7 67.8 68.2 65.1 101.8 102.3 95.8
Nonfast
SE 0.7 0.5 3.4 3.6 1.5 3.3 4.0
i
X = Mean SE = Standard error of the mean A = Change

SBP = Systolic blood pressure

GL = Ground level altitude (390 m MSL)
Alt. = Hypobaric chamber altitude of 3,810 m MSL
Alt. 2 = Ten-min resting period at 50-60 min of the first hour at

altitude

DBP = Diastolic blood pressure

Alt. 3 = Ten-min resting period at 48-58 min of the second hour at

altitude immediately preceding the simulated +2Gz test

+2Gz = Two-min period of -40 mm Hg LBNP at 58-60 min of the second
hour at altitude


Technical Report Documentation Page

T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.
FAA-AM-81-2
4. Title and Subtitle 5. Report Date

February 1981

&. Performing Organization Code

CARDIORESPIRATORY ASSESSMENT OF 24~HOUR CRASH-DIET
EFFECTS ON ALTITUDE, +Gz, AND FATIGUE TOLERANCES

8. Performing Organization Report No.

7 Authors)

Michael T. Lategola, Peggy J. Lyne, and Mary J. Burr

9. Performing Organization Name ond Address 10. Work Unit No. (TRAIS)
FAA Civil Aeromedical Institute Tin Connect ar Grant No
P.O. Box 25082 . .

Oklahoma City, Oklahoma 73125

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 Agency Code

Washington, D.C. 20591

15. Supplementary Notes

Work was done under approved tasks AM-A-80-PHY~122 and AM~A~-81-PHY-122.

16. Abstract

Eleven male surrogates of general aviation pilots, 25-40 years old, were tested for
altitude, +Gz, and fatigue tolerances with and without previous fasting for 24 h.
Testing included 2 min of lower body negative pressure (LBNP) at -40 torr (equiva-
lent to +2Gz) after 118 min at 3,810 m chamber altitude and, after returning to
ground level pressure, ergometry of 50 watts (W) for 6 min. The fast had no statis-
tically significant effect on altitude and fatigue tolerances. One subject, who
tolerated 2 min of LBNP in the nonfasting condition, lost useful consciousness dur-
ing this test in the fasting condition. Although the remaining 10 subjects toler-
ated 2 min of LBNP in both fasting and nonfasting conditions without statistically
significant differences in quantitated parameters, 2 of them during fasting mani-
fested symptoms usually associated with impending syncope. Pilots should be
informed that a 24-h fast may reduce the margin for safe tolerance of > +2Gz

flight maneuvers.

17. Key Words 1B. Distribution Statement

General aviation pilots, Crash diet, Document is available to the public through
Cardiorespiratory assessment, Altitude |the National Technical Information Service,
tolerance, +Gz tolerance, Fatigue Springfield, Virginia 22161

tolerance

19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages | 22. Price
Unclassified Unclassified 20

Form DOT F 1700.7 (8-72)

Reproduction of completed page authorized


TABLE VII. V,/kg, £, and Vp/kg

%_A Va/kg
Ve/kg (1/min/kg) Alt, 2 Alt. 3 +26z
Ge «Alt. 2 Alt. 3 +2Gz ep R100 GE X100 aie, 3 X 100
xX 74.2 | 91.9 | 91.5 | 105.2 125.1 124.5 116.1
Fast
SE 3.1 45 5.0 6.0 7.0 7.2 6.8
x 76.8 | 92.4 | 95.4 | 98.3 120.7 125.0 102.9
Nonfast |
SE 3.0 4.4 | 3.7 5.0 4.4 4.8 3.6
i
ZAE
£ (rpm) Alt. 2 Alt. 3 +2Gz
Gl Alt. 2 Alt. 3 42Gz cL 100 “Gr 100 Are 3 X 100
s {
x 13.1 | 14.5 | 13.6 | 14.9 111.2 104.4 111.8 |
Fast
SE 0.7 1.2 1.0 1.2 10.0 6.0 8.0 |
=
x 13.0 | 13.8 | 13.7 | 13.8 108.9 108.8 102.5!
Nonfast t
SE 0.8 1.0 1.0 1.2 10.4 11.8 7.9003
L i
%_A Vp/kg
Vp/kg (ml/kg) Alt. 2 Alt. 3 +2G6z
GL Alt. 2 Alt. 3 +2Gz gp 100 “GE X100 are! 3 ¥ 100
¢
x 5.8 7.0 7.0 7.4 122.2 123.0 107.5
Fast
SE 0.3 1.0 0.5 0.7 15.7 10.1 7.4
xX 6.1 6.8 TA 7.5 115.9 121.6 105.8
Nonfast
SE 0.4 0.3 0.4 0.5 6.6 9.1 7.0
X = Mean SE = Standard error of the mean 4 = Change

Alt. = Hypobaric chamber altitude of 3,810 m MSL GL = Ground level altitude (390 m MSL)

Vg/kg = Pulmonary ventilation per kilogram of body weight

V.p/kg = Tidal volume per kilogram of body weight

Alt. 2 = Ten-min resting period at 50-60 min of the first hour at altitude

Alt. 3 = Ten-min resting period at 48-58 min of the second hour at altitude immediately
preceding the simulated +2Gz test

£ (rpm) = Respiratory frequency in respirations per min

+2Gz = Two-min period of -40 mm Hg LBNP at 58-60 min of the second hour at altitude

11


TABLE VI. TAFV and HR

%_h TAEV
TAFV_ (cm/s) Ale. 2 Alt. 3. +2Gz
Gl Alt. 2 Alt. 3. 42Gz Gp 100 “GX 100 are 3x 100
x 4.7 4.0 4.7 | 3.4 86.8 101.2 74.5
SE 0.6 0.5 0.5 | 0.4 8.1 8.7 4.0
x 4.5 4.1 4.6 | 3.7 92.9 103.1 79.2
Nonfast
SE 0.4 0.6 0.5 | 0.4 8.7 5.9 2.3
% AHR
HR (bpm) Alt. 2 Alt. 3. +2Gz
Gl Alt. 2 Alt. 3 4202 GX 100 “GEk 100 aye 3x 100
x 73.3 78.2 | 82.4 | 94.5 107.1 112.9 114.0
SE 3.6 4.3 4.0] 4.7 3.5 3.8 4.0
x 76.4 80.8 | 81.0 | 89.7 106.4 107.1 111.5
Nonfast
SE 4.6 4.1 4.0] 3.6 2.6 3.8 3.1
X = Mean SE = Standard error of the mean 4 = Change

TAFV = Temporal artery blood flow velocity

HR (bpm) = Heart rate in beats per min

L = Ground level altitude (390 m MSL)

Alt. = Hypobaric chamber altitude of 3,810 m MSL

Alt. 2 = Ten-min resting period at 50-60 min of the first hour
at altitude

Alt. 3 = Ten-min resting period at 48-58 min of the second hour
at altitude immediately preceding the simulated +2Gz test

+2Gz = Two-min period of -40 mm Hg LBNP at 58-60 min of the second

hour at altitude

10


TABLE III. Blood Chemistry

Glucose Hemoglobin Hematocrit
Dy Dy Dg Dy Dy Dg Dy Dy D2
(gm/d1) (gm/d1) —x 100 (gm/d1) (gm/d1) —x 100 (2) (4) —X 100
Dy Dy Dy
sy
x 86.8 82.3 95.1 13.9 14.6 | 104.7 40.4 42.3 | 104.8
Fast * *
SE 1.8 0.8 1.9 0.2 0.3 0.7 0.6 0.6 1.0
xX 88.9 88.5 99.9 14.4 14.3 99.6 40.9 41.0 | 100.3
Nonfast
SE 1.9 1.7 2.7 0.2 0.2 0.7 0.6 0.7 0.3
% 4 Blood Volume % 4 Plasma Volume
D2/D, X 100 D/D, X 100
x 95.6 92.5
Fast * *
SE 0.6 1.1
x 100.4 100.2
Nonfast
SE 0.7 0.7
X = Mean SE = Standard error of the mean
Dy = Day 1 Dy = Day 2 A = Change

Alt. = Hypobaric chamber altitude of 3,810 m MSL

* = Statistically significant difference with a
probability value of p < 0.05



TABLE I. Vital Statistics

Age Height Weight No.
(yr) (cm) (kg)
x 27.1 177.7 89.6 10
SE 2.1 1.9 2.3
t 32.0 186.7 97.2 1
X = Mean SE = Standard error of the mean

+ = The one subject who was qualitatively incapacitated during
LBNP testing. at altitude after a total food fast of 24 h



TABLE IX. Postaltitude Ergometry (10 Minute Resting Control)
SBP DBP PP AP HR
(mm Hg) (mm Hg) (mm Hg) (mm Hg) (bpm)
x 115.7 69.4 46.2 84.8 75.8
Fast
SE 2.8 3.1 3.9 2.3 3.9
xX 120.3 71.0 49.2 87.4 72.5
Nonfast
SE 2.2 2.6 3.1 2.0 41
Vo2/kg TAFV Vp/kg f Vp/kg,
(ml/min./kg) (cm/s) (ml /min/kg) (rpm) (m1/kg)
xX 2.8 5.4 74.8 13.2 5.8
Fast
SE 0.1 0.4 2.9 0.8 0.3
x 2.9 4.8 76.6 13.1 6.0
Nonfast
SE O.1 0.5 3.1 0.9 0.4
X = Mean SE = Standard error of the mean

SBP = Systolic blood pressure
DBP = Diastolic blood pressure

PP
AP

Pulse pressure
Mean arterial pressure, calculated as the value of DPB + 1/3 PP
HR (bpm) = Heart rate in beats per min

Alt. = Hypobaric chamber altitude of 3,810 m MSL

VO/kg = Oxygen uptake per kilogram of body weight

TAFV = Temporal artery blood flow velocity
Vy/ke = Pulmonary ventilation per kilogram of body weight
£ (rpm) = Respiratory frequency in respirations per min

Vep/kg = Tidal volume per kilogram of body weight

14



In the remaining 10 subjects under the fasting condition, the 2 min of
LBNP at altitude produced statistically significant displacements in systolic
blood pressure (SPB), pulse pressure (PP), mean arterial pressure (AP), TAFV,
HR, and VE/kg which were greater in magnitude than the corresponding displace-
ments in these 10 subjects under the nonfasting condition. Although the fast-
ing displacements were greater and statistically significant, per se, the dif-
ferences between them and the corresponding displacements under the nonfasting
condition were not statistically significant.

Under the nonfasting condition, the same 10 subjects easily tolerated
the 2 min of LBNP at altitude with either no symptoms, or with few symptoms
which were mild, transient, or nonintensifying. Under the fasting condition,
8 of the 10 subjects postexperimentally reported an increase in the presence
and/or intensity of symptoms during the LBNP. Two of these eight subjects
felt that they were nearing syncope at the end of the 2 min of LBNP, because
lightheadedness was present and increasing, nausea was commencing, and visual
blurring and graying was present and progressing. Visual tunneling had com-
menced in one of these two subjects. Both of them fully recovered upon ces-
sation of the LBNP.

Consistent with a comprehensive review of LBNP research findings (29),
and with the subjective and objective data of this study, it appears reasonable
to suggest that the threshold for syncopal intolerance to 2 min of -40 torr
LBNP (+2Gz) possesses a distribution spectrum; and that in the fasting condi-
tion of this study, two subjects did not approach the threshold, six of them
were approaching the threshold at individual rates, two were probably right at
the threshold, and one exceeded the threshold. If the threshold of intolerance
to this LBNP test was approximated during fasting by three of the subjects,
whose adequate tolerance of the same test during orientation revealed their
biased position in the more tolerant portion of the distribution spectrum of
this function, then it follows that intolerance should probably occur more
frequently in a random sample of general aviation pilots without this selec-
tion bias.

The decrements in both circulating biood and plasma volumes, which are
caused by total fasting, constitute the primary physiological changes relevant
to a potential decrease in +Gz tolerance. Several studies have reported
decreased +Gz or LBNP tolerances as a consequence of reducing blood and plasma
volumes by any of several means (10,20,22,28,29). In our study, the mean
decrements in both blood and plasma volumes after the 24-h fast constituted
statistically significant differences (Table III) from the corresponding
changes which occurred in the nonfasting condition. In the one subject, who
was incapacitated during LBNP after the 24-h fast, the blood and plasma vol-
ume decrements were of the same order of magnitude as the two subjects who
felt that they were nearing syncope at the end of the LBNP test.

Intake of caffeine, which has a well-known diuretic action, was not
allowed in both the fasting and nonfasting experiment sessions. Despite
the fact that caffeine diuresis could possibly have caused a further decrease
in the blood and plasma volumes, and hence possibly have made the fasted
individuals more susceptible to syncope during the LBNP, we chose to omit it

16


pressure equivalent of ground level (GL) altitude (388 m), the subject
underwent 4 min of pedal ergometry at the moderate load of 50 watts (W).
During this protocol orientation, the subject was disqualified from sub-
sequent participation if his arterial oxygen saturation (Hb02) did not
remain above 80 percent during the hypobaric exposure, useful conscious-
ness was not maintained during the 2 min of LBNP at altitude and, his

heart rate (HR) exceeded 150 beats per min (bpm) during the pedal ergometry.
Additionally, disqualification resulted if the subject's single-lead elec-
trocardiogram (ECG) manifested evidence of ischemia and/or arrhythmia at

any time during the orientation. Age, height, and weight of the 11 sub-
jects are show in Table I.

Protocol and Parameters. Each subject participated in one experiment
per week for 2 consecutive weeks. The experimental protocol is outlined
in Table II. Each subject reported at 0745 after fasting overnight. He
voided his urine, and donned a surgical scrub suit. His body weight, cor-
rected for clothing weight, was measured. A venous blood sample was drawn
and heparinized; blood glucose (25), hematocrit, and hemoglobin (19) were
measured. The hematocrit and hemoglobin data, along with corresponding
data from the blood sample drawn 24 h later, were used in calculating the
percent change in blood and plasma volumes (7).

At 0800 the subject ate a standard breakfast. In the fasting experiment,
the subject ate nothing further until 1300 on the next day. Only water and
no~calorie soft drinks were permitted during the fasting period. Adherence
to fasting was monitored at all times. In the control (nonfasting) experi-
ment, the subject was fed a lunch at 1300, a dinner at 1800, a breakfast at
0800 on the next day, and was allowed to consume snack foods and drinks at
any time. Drinks containing caffeine were withheld from all experimental
sessions. During the first day of each experiment, the subject remained in
an upright body position, and refrained from sleeping.

The subject went to bed at 2300 on the first day and arose at 0700 the
next day. At 0745 he voided his urine, was weighed, and had a blood sample
drawn, In the nonfasting experiment, breakfast was eaten at 0800. At 0830
the subject entered the hypobaric chamber and was instrumented for subsequent
testing. The subject was seated upright in the LBNP box and sealed in it
from the waist down. The LBNP box and its built-in pedal ergometer have been
described elsewhere (15). Physiological measurements were recorded for 10
min at GL, after which the chamber pressure was reduced over a 10 min period
to an altitude equivalent of 3,810 m. At altitude, four separate math tests
were alternated with 10-min periods of resting physiological measurements as
indicated in Table II. After 1 h and 48 min at altitude, 10 min of resting
measurements were made, after which the subject was exposed to -40 torr LBNP
for 2 min. The chamber pressure was then returned to GL pressure in 10 min.
A 10-min period of resting measurements preceded pedal ergometry of 30 W for
2 min, and 50 W for 6 min. After ergometry testing, all sensors were removed.
The subject voided his urine, was weighed and allowed to don his street
clothes. He returned 6 d later at the same time (0745) for the second experi-
ment session. To compensate for any effects of experimental order, half of
the subjects were fasted in the first experiment session and the remaining


CARDIORESPIRATORY ASSESSMENT OF 24-HOUR CRASH-DIET
EFFECTS ON ALTITUDE, +Gz, AND FATIGUE TOLERANCES

INTRODUCTION

Studies of acute starvation (up to 10 d) in healthy humans (4,5) have
revealed that reductions in blood and plasma volumes occur during fasting
despite the administration of supplementary water. The largest decrement in
total body water occurs during the first day of fasting (4). Dehydration has
been demonstrated to cause increased fatigability (23), and decreased toler-
ance to gravity (G) (20,22,29). Overnight fasting significantly decreased
the tolerance of healthy men to a hypoxic altitude equivalent of 4,875 m
mean sea level (MSL) (12). The tolerance of nonfasting healthy men to 1.5
min of lower body negative pressure (LBNP) equivalent to +2Gz was signif-
icantly reduced at the hypoxic altitude equivalent of 4,145 m MSL as com-
pared to a sea level normoxic altitude equivalent (13). These findings
(12,13) suggest the possibility of a decreased +Gz tolerance (+2Gz for 2
min) in healthy men under the combination of total food fasting and ambient
air breathing at a 3,810 m MSL altitude.

The National Center for Health Statistics has reported that United
States men, 18-75 years of age, were 1.4 kg heavier during a 1971-1974 sur-
vey than were men surveyed during 1960-1962 (1). An evaluation of the
earlier survey revealed that about 70 percent of these men were overweight
(11). The 1978 height and weight data for male general aviation pilots
reflect a similar presence of overweight (8).

Dieting has become a fashionable means of reducing body weight. One
popular version is the crash diet, which requires complete abstinence from
all food intake for about 24 h. Because loss of body water is greatest dur-
ing the first 24 h of such a diet (4), and because such loss of body water
may possibly decrease altitude, +Gz, and fatigue tolerances (12,20,22,23,
29), this study was undertaken. The purpose of this investigation was to
assess the effects of crash dieting on tolerance to fatigue under a submaxi-
mum physical workload, to LBNP (equivalent to +2Gz) and, to a moderate alti-
tude (3,810 m). For this study, crash diet is defined as total abstinence
for 24 h from the intake of food, but not water.

METHODS

Subjects. Paid, healthy male volunteers, 21-35 years old, who were
5-15 percent overweight were used. The weight-per-height norms of the
Framingham Study (6) were used as the basis for calculating the 5-15 per-
cent range of overweight. In order to qualify medically as a surrogate,
each subject had to pass a physical examination, which was equivalent to
third-class medical certification of a general aviation pilot. Those medi-
cally qualified signed a standard consent form after a thorough briefing.
Each subject was then given a complete equipment and protocol orientation.
This included a 0.5-h exposure in our hypobaric chamber to the pressure
equivalent of a 3,810 m altitude MSL, during which the subject took a timed
simple math test, and then underwent 2 min of LBNP equivalent to +2Gz (-40
torr relative to chamber pressure). After the chamber was returned to the


TABLE VIII. Hb02

% & Hb02
HbO»9 (% sat.) Alt. 2 Alt. 3 +2Gz
GL Alt. 2 Alt. 3 42¢z GL * 100 “gr 100 aig, 3X 100
x 95.4 85.1 86.5 | 88.7 89.3 90.7 102.6
Fast
SE 0.3 1.2 1.2 0.9 1.3 1.2 ll
x 94.6 85.0 85.3 187.5 89.9 90.2 102.6
Nonfast
SE 0.6 0.8 0.8 0.9 0.6 0.6 0.6
X = Mean SE = Standard error of the mean A = Change
HbO2 = Arterial oxyhemoglobin saturation
GL = Ground level altitude (390 m MSL)
Alt. = Hypobaric chamber altitude of 3,810 m MSL
Alt. 2 = Ten-min resting period at 50-60 min of the first hour
at altitude
Alt. 3 = Ten-min resting period at 48-58 min of the second hour
at altitude immediately preceding the simulated +2Gz test
+2Gz = Two-min period of -40 mm Hg LBNP at 58-60 min of the second

hour at altitude

12



TABLE X. Postaltitude Ergometry (50 W Load)

SBP DBP PP AP HR
: (am Hg) (mm Hg) (am Hg) (mm Hg) (bpm)
‘
x 145.6 70.8 74.8 95.7 111.4
Fast
SE 3.8 3.3 4.3 2.8 3.1
_ |
x 152.7 72.3 80.4 99.1 110.0
Nonfast i
SE |; 3.4 2.6 3.9 2.2 3.1
4
You/kg TAFV Vp/ke £ Vep/kg
(ml/min/kg) (cm/s) (m1 /min/kg) (rpm) (mi/kg)
xX 10.0 5.8 234.9 19.2 12.5
Fast
SE 0.4 0.4 12.8 1.1 0.7
x 9.5 5.5 236.1 19.9 12.2
Nonfast
SE 0.5 0.5 13.8 1.2 0.9
X = Mean SE = Standard error of the mean
SBP = Systolic blood pressure
DBP = Diastolic blood pressure PP = Pulse pressure

AP = Mean arterial pressure, calculated as the value
of DBP + 1/3 PP
HR (bpm) = Heart rate in beats per min
Alt. = Hypobaric chamber altitude of 3,810 m MSL
VWOo/kg = Oxygen uptake per kilogram of body weight
TAFV = Temporal artery blood flow velocity
Vp/kg = Pulmonary ventilation per kilogram of body weight
£ (rpm) = Respiratory frequency in respirations per min
Vq/kg = Tidal volume per kilogram of body weight

15