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screening norm for acceptable tolerance to general aviation
altitudes.

The moderate degree of FEF 4 575% impairment (65,1 percent

of predicted normal values) did not appear to diminish normal
tolerance to an altitude-exposure profile somewhat represen-
tative of average maxima encountered in general aviation
flights under ambient air breathing conditions. Whether this
same degree of spirometric impairment constitutes an incursion
to any degree on other critical aspects of flight safety,

such as fatigue and orthostatic tolerances, remains to be
ascertained empirically, Such studies are currently under
consideration,


Summary of Blood Pressure Data

TABLE 2.

SBP(mm Hg)

AL

GL

wet ad an fat nol ao on} ne
co st at obtanpon opto fon mp antan
a N < 5 ~~ < + to. < -) i)
a a
aa Cons) nao lor tapos on fost
an a4 afbon|wa ap andra afpandtan
a nN < 6 6 < + t+ <= an 0
a a
ain aN aA fon ny om pna > wot pana
oe ere leet one oat oe en as oe
at ao wap rnam lod mooaftan fon rfp antan
N Nn at ~ ~ < + + < an a
= 1s i E

E £ Ss

LS a

a au a

a

a
an NN © antlan nal no wolow
at aon a Ra fon a tapos a amndban
N N oO é ~ oO + + oO an an
my 4

: & = = = =

a ai a fl a fa a i
InD [ixXD Ix fix a Ix |IKD Ina [ina
a H zB 4 a H a H
a a a a a a a a



III.

midway (A) and the end (ag) of the 12,500-ft altitude period.

Each parameter was assessed during steady-state conditions

as the mean value of a 2-min sampling period. Systolic (SBP)
and diastolic (DBP) blood pressures were measured by auto-
matically cycled auscultative sphygmomanometry and expressed
in mm Hg. Pulse pressure (PP) and mean arterial pressure (AP)
(8) were calculated from the SBP and DBP data. Pulmonary
ventilation (VE) was measured by a precalibrated mass flowmeter
(10). An oral breathing valve and nose clip allowed the con-
tinuous flow-by measurement of each exhalation. To normalize
differences in body size, we expressed all VE measurements as
ml/min/kg body weight at body temperature and pressure,
saturated (BIPS) conditions, Arterial oxyhemoglobin satura-
tion, expressed in percentage (% HbO,), was measured with

an ear oximeter (14). Temporal artery blood-flow velocity
(TAFV) was measured with an externally positioned Doppler
device and expressed in cm/s (7). This device senses the
direction as well as the velocity of flow (7). Electro-
cardiographic function was monitored with the CM, single-lead

electrocardiogram (ECG) (2). The electrical signal from this
ECG lead was fed simultaneously to: (i) an oscilloscope for
continual visual monitoring of the signal for ischemia and/or
arrhythmia; (ii) a cardiotachometer for continual indication
of heart rate (HR); and (iii) a standard ECG recorder for
scheduled periodic recording and opportunistic recording of
any substantial ECG changes as observed simultaneously on the
oscilloscope. Steady-state HR measurements in beats/minute
(bpm) were obtained from either the pulsatile mode of the
TAFV recording or that of the single-lead ECG.

Each subject was given a comprehensive equipment and pro-
cedure orientation preceding the day of the experimental run.
All the subjects had had at least one prior training experi-
ence in an altitude chamber, All altitude exposures were
monitored by a staff physician.

Results.

The cardiorespiratory parameters assessed for altitude
tolerance in both the SN and SI pilot groups are summarized
in Tables 2 and 3, In general, only small quantitative
differences between the SN and SI pilots emerged from these
data, and none of these differences was statistically signi-
ficant at the probability level of 0.05 or less, At altitude,

4


Iv.

blood pressure functions appeared to be maintained quite well
in both groups, Although statistically nonsignificant, the
altitude hypoxia appears to have displaced the SI group more
than the SN group. This displacement is indicated in the
relatively higher SBP, PP, HR, and TAFV values at altitude.

The % HbO, of the SI group was maintained quite well at the

higher of the two altitudes at the apparent cost of a slightly
greater VE than that of the SN group.

None of the 20 pilots who took part in this study mani-
fested any ischemic ECG changes at GL or at either altitude.
Two of the SN and one of the SI pilots manifested unifocal
premature ventricular contractions (PVC) in their respective
ECG recordings at GL. The PVC frequency in all three cases
was quite low. Because the PVC frequency did not increase,
and the otherwise normal character of the three ECG tracings
did not deteriorate at both altitudes, this condition was
medically judged to be benign, It may be a random coincidence,
but all three of these pilots are chronic cigarette smokers.

Discussion and Summary.

As previously reported (9), spirometric assessment of
181 male general aviation pilots revealed moderate degrees
of impairment in 12.7 percent of this population sample,
This moderate impairment was manifested mainly in the two
spirometric parameters (FEV, 2% and FEF 5754) usually deemed

most sensitive in the detection of functional decrements in
the peripheral airways. All the other assessed spirometric
parameters were found to be grossly normal. Peripheral
airway impairment is considered to be one of the earliest
manifestations of COPD (6).

Because the altitude tolerance of the 10 SI pilots
appeared to be generally equal to that of the 10 SN pilots,
the detection of a pilot having any possibility of spiro-
metrically related intolerance to the sedentary altitude
profile used in this study would have to be reflected by a
greater spirometric degradation than just an FEF 5.75% value

of 65.1 percent. Conversely, any smaller spirometric decre-
ment should be predictive of normal tolerance to the same
altitude profile. Therefore, one distinct value of this study
is the delineation of an objective FEF 55757 spirometric



ACKNOWLEDGEMENTS

The authors gratefully acknowledge the participation of the
20 pilots who volunteered as subjects for this study. Also
acknowledged is the skillful assistance of the altitude
chamber operators of the Physiological Operations and Training
Section, Aeromedical Education Branch.



ll.

12,

13.

14,

Morris, J. F., A. Koski, and L, C. Johnson: Spirometric
Standards for Healthy Nonsmoking Adults, AM. REV. RESP. DIS.,
103:57-67, 1971.

Roberts, J.: The Mortality from Emphysema and Bronchitis Still
Go Up, PUBLIC HEALTH REPORTS, 90:382-383, 1975.

Roberts, J.: Weight by Height and Age of Adults, VITAL AND
HEALTH STATISTICS, Series II, No. 14, 1966.

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,

10


1.

10.

REFERENCES

American Lung Association and American Thoracic Society: Report
of the Task Force on Comprehensive and Continuing Care for Patients
with Chronic Obstructive Pulmonary Disease, American Lung
Association, 1975, p. 3.

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 M. J.
Karvonen and A, Barry (Ed.), Physical Activity and the Heart,
Springfield, Illinois, A. H. Thomas, 1966, Chapter 9, pp. 101-134,

Catlett, G. F., and G. J. Kidera: Detection of Respiratory
Impairment in Pilots, AEROSPACE MED., 40:1252-1257, 1969,

Dawber, T, R., F. E. Moore, and G. V. Mann: Coronary Heart Disease
in the Framingham Study, J. PUB. HEALTH, 47 (Suppl.): 4, 1957.

FAA Office of Aviation Medicine: Guide for Aviation Medical
Examiners, Washington, D.C., U.S. Government Printing Office,
p. 40, 1970.

Gelb, A. F., and B. J, MacAnally: Early Detection of Obstructive
Lung Disease by Analysis of Maximal Expiratory Flow-Volume Curves,
CHEST, 64:749-753, 1973.

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

Lamb, L. E., R. L. Johnson, and P, M. Stevens: Cardiovascular
Deconditioning During Chair Rest, AEROSPACE MED., 35:646-649, 1964.

Lategola, M. T., M. Flux, and P. J. Lyne: Spirometric Assessment
of Potential Respiratory Impairment in General Aviation Airmen,
FAA Office of Aviation Medicine Report No. AM-77-3, 1977.

Londeree, B. R.: Validation of the Oxygen Consumption Computer,
MED. SCI, SPORTS, 5:187-190, 1973.



nin
no

+0
to

a+
nao

OK)
net

HR(bpm)
TAFV(cm/s)

al
+o

na
no

VE(ml/min/kg body weight)

GL
GL
106.9
11.0
GL
GL

nt
to

on
wo

Summary of Heart Rate, Pulmonary Ventilation, Arterial

Oxyhemoglobin Saturation, and Temporal Artery Blood
Flow Velocity Data

TABLE 3.

SN
SI
SN
SI
SN
sI

SEM

SN

SEM

SI



II.

Whether the quantitated minor-to-moderate spirometric
impairment observed in the previous study (9) compromises
safe flight to any degree can be ascertained only by testing
such spirometrically impaired pilots in critical aspects of
flight safety, such as altitude, fatigue, and orthostatic
tolerances, This present study deals with the assessment
of altitude tolerance in a sample from this same group of
pilots.

Materials and Methods.

Selection of Subjects. Volunteer males were recruited
from subjects of a recently completed study on spirometric
assessment (9), Each volunteer was currently a medically
certified general aviation pilot. For the purpose of this
study, spirometric impairment was defined as an FEF 575%

value of less than 80 percent of the predicted normal value.
The predicted normal values for this parameter are based
on the study of Morris et al. (11). Ten pilots having an
average FEF 95.75% value of 65.1 percent composed the spiro-

metrically impaired (SI) group. All their other spirometric
parameters were grossly normal, The altitude tolerance of
this group was compared to a group of spirometrically normal
(SN) pilots. Spirometric normality is defined here as a
value of 80 or more percent of the predicted normal value
for all five spirometric parameters assessed in the preceding
study (9). The FEF )5_757 values of the SN pilots covered a

range of 102.0-140.2 percent of their predicted normal
values, These two groups were age-matched as closely as
possible. Each group contained eight smokers, one ex~smoker,
and one nonsmoker. The vital statistics of both groups are
presented in Table 1.

Protocol and Parameters. Cardiorespiratory functions
were assessed in each pilot seated comfortably while breathing
only ambient air in an altitude chamber during consecutive
periods of 10 min at ground level (GL), 15 min at 8,000 ft,
and 30 min at 12,500 ft. The interaltitude excursion rate
was controlled at approximately 1,000 ft/s. The average altitude-
chamber temperature for all 20 experiments was 23.5° Cc,

All specific parameters were assessed at the end of the GL
period, the end (a) of the 8,000-ft altitude period, and both


I.

ALTITUDE TOLERANCE OF GENERAL AVIATION PILOTS WITH
NORMAL OR PARTIALLY IMPAIRED SPIROMETRIC FUNCTION

Introduction.

Recent studies indicate that the prevalence of chronic
obstructive pulmonary disease (COPD) is increasing in the
United States population (1,12), and the risk of its
incurrence is estimated at 5 to 10 times greater in men than
in women (3), Several variations of COPD of "sufficient
degree to be symptomatic" and/or "to interfere with pulmonary
function" are among the conditions for which medical certi-
fication of airmen is denied or deferred (5). Unless clini-
cally indicated, quantitative spirometric evaluation is not
a mandatory part of the aeromedical examination. Quanti-
tative spirometry in a recent study of 257 commercial
airline pilots (40-59 yr of age) showed that minor-to-
moderate spirometric impairment existed in 12 percent of
this population sample and was highly correlated with age
and cigarette smoking (3). Substantial degrees of spiro-
metric impairment could adversely affect safe flight by the
general aviation pilot breathing only ambient air at cabin
altitudes approaching 12,500 ft.

Because commensurate spirometric data from general
aviation pilots did not appear to exist in the published
medical literature, a parallel study was made. The forced
vital capacity (FVC), the l-s forced expired volume (FEV,),

the forced midexpiratory flow (FEF, 5 754) the FEV, /FVC x
100 (FEV,4), and the maximum ventilatory volume were quanti-

tatively assessed in 181 male general aviation pilots. This
population sample included nonsmokers, smokers, and ex-smokers
in approximately equal numbers. Based on the combined data

for FEV, % and FEF) 5_9579 minor or greater degrees of spiro-

metric impairment were manifested by 25.4 percent of the
pilots and moderate or greater degrees by 12.7 percent. Most
of the impairment was manifested in the smokers and ex-smokers.
The first sharp rise in moderate impairment for these two
subgroups occurred in the fourth decade of age. Details of
this study have been published in a previous report (9).