to search for useful correlations not obviously
discernible.

The demand on this laboratory’s creative
capability is demonstrated in an all electronic
measuring and magnetic tape recording system
in the Cardiovascular Laboratory and a new
analog computer for the reduction of pulmonary
function data.

The range of activities of this laboratory in-
cludes the design and development of trans-
ducers for measuring physiological function,
data conditioning systems, data acquisition sys-
tems, on-line and off-line data reduction systems
and the application of the latest state-of-the-art
in biophysics and electronics to problems in civil
aviation medicine.

Computer demands and statistical guidance
for the appropriate analysis in such a program
are evident, so that the inclusion of epidemio-
logical supervision for our staff is mandatory.
Eventually, a verification of laboratory studies
is planned in an airborne environment.

12

In conclusion we may say that we can hope,
with several years of consecutive studies on in-
dividuals, to:

1. Develop from the foregoing procedures a
significant set of techniques by which the physi-
ological aging rating for that individual may
be ascertained.

2, Develop a profile of physiological capabil-
ities which insures performance demand.

3. Develop more refined techniques of eval-
uating the significance of pathological states,
as well as their detection at the earliest possible
age, so that some alleviation may be effected to
preclude the ultimate development of incapaci-
tating decrements.

4, Aid in the formulation of physical stand-
ards determined by physiological rather than
chronological age, thus lengthening the produc-
tive period in the life of qualified aviation
personnel.

‘FrU,S. GOVERNMENT PRINTING OFFICE: 1964 O—748-~490


STUDIES ON AGING
IN AVIATION PERSONNEL

Civil aviation represents an area of activity
which, in its various facets, is obliged to deal
with the entire age range of the general popu-
lation, both in its user and in its operational
personnel. Thus it presents to the Federal
Aviation Agency, its regulatory agency, prob-
lems which are unique in many respects, and
which have not been encountered in the develop-
ment of military aviation activities, since the
latter does not engage in extensive air carrier
activities and its operational personnel are sub-
ject to mandatory limitations. Therefore, the
Federal Aviation Agency, in the organization
of its medical service and in acknowledging the
importance of identifying in the individual air-
man decrements in performance resulting from
physiological changes (some of which are noted
to occur more rapidly in certain individuals
than in others), created an Aeromedical Re-
search and Education Division.

The AR&E Division is charged with the
responsibility of accurately detecting such
changes, as well as with investigating the hu-
man factors problems affecting safety in flying.
This research is necessary because at the present
time no medical methods exist for evaluating
an adult human being in terms that will provide
a useful estimate of his overall status as an
aging individual. To make fullest use of the
extensive experience and skills developed by
older air crewmembers, it is necessary to develop
medical guidelines to determine when decreas-
ing capabilities cancel the benefits of experience.
This becomes an increasingly important con-
sideration as additional technical demands of
high-speed aircraft evolve.

Chronological age fails to serve as an accurate
index of the rate at which these capabilities
change in every individual. Men who are in
their fifth and sixth decades may demonstrate a
physiological performance commensurate with

second- and third-decade function, whereas
young men may be “old for their age.” This
particular study in FAA’s research effort is
oriented toward improving methods for more
accurate measurements of these changes and for
their detection at the earliest possible chrono-
logical age.

To insure the validity of the results of such
research, which will proffer, ultimately, guide-
lines to a Federal regulatory agency and to
acquire the professional talents and capabilities
needed to undertake studies of this proportion,
the Federal Aviation Agency has sought to
integrate its research facilities with those of
universities which are outstanding in their re-
search efforts. Such a group of medical scien-
tists has undertaken the clinical aspects of the
problems of aging in aviation personnel, orga-
nized as the Georgetown Clinical . Research
Institute, located in. the Georgetown Univer-
sity Medical Center in Washington, D.C.

Significant aging changes may be identified
in all physiological systems. The changes in
some systems can be evaluated with greater
facility and offer a closer age correlation than
others, so that in selecting a battery of studies
which could reasonably be expected to reflect
significant aging changes, and where existing
techniques afford promise of refinement, these
several factors were taken into consideration.
Investigative work has therefore been under-
taken in the cardiovascular, neurological, pul-
monary, visual and. auditory, and biochemical
systems, and to appropriately relate the func-
tional status of these systems to performance,
behavioral tasks have been incorporated in the
individual survey.

The format of an aging study, if an indi-
vidual evaluation of the physiological compe-
tence of each airman is to be identified with
the passage of time, must be one of a longi-



alter the O, dissociation curve may occur in the
“normal” population with some degree of fre-
quency. Since alterations in the O, dissociation
curve may be of significance in determining
tissue oxygen delivery on exposure to low at-
mospheric O, tensions, this area warrants
consideration.

A series of patients free from detectable
cardiopulmonary disease and ranging in age
from 20 years upward will be studied. Each
study will include one or more of the following
measurements :

1, Static lung volumes.
2. Dynamic lung volumes.
8. Helium mixing time.
4, Minute ventilation, oxygen uptake and

CO, output.
. “Single breath” nitrogen test.
. Nitrogen clearance curve.
. “Single breath” carbon monoxide dif-

fusing capacity.
. “Steady state” carbon monoxide diffus-

ing capacity.

9, “End-tidal” carbon dioxide tension.

10. O, dissociation curve.

11. Oxygen cost of respiration during var-

ious maneuvers.
12. Ventilatory response to exercise, CO.-
rich and oxygen-poor gas mixtures.
The above battery obviously cannot be carried

out in the required 30-60-minute time period.
It is planned, therefore, to study small “pilot
groups” of approximately 100 subjects with one
or more components of the above battery to
ascertain which measurements are providing
first, the most reproducible data (in terms of
the lack of first vs. second test variation on
the same day) and second, the most promising
data in terms of age-related trends. As such
information becomes available, certain tests will
be chosen for inclusion in the eventual standard
protocol for establishing a PAR with regard to
pulmonary function, while others will be
dropped from the study schedule. Thus, in
stepwise fashion an ultimate standard protocol
will be derived. This standard protocol will
then be applied in a large series of subjects
(300-500), and the results of individual tests
will be correlated’ with one another and with the

nos

@~

data obtained in other sections of the clinical
research institute.

The high-altitude, high-speed nature of mod-
ern aircraft offers a number of actual and poten-
tial situations wherein acute or chronic altera-
tions in pulmonary function may have a bearing
upon pilot performance and passenger safety.
Certain alterations in respiration may produce
undesirable physiologic changes in patients with
normal pulmonary function, changes which may
be exaggerated in subjects with underlying pul-
monary or cardiovascular disease. Other respi-
ratory alterations may be important only in
persons with significant pre-existing pulmonary
disease.

Ayperventilation is a frequent accompani-
ment of high-altitude flying and of a variety
of anxiety-producing situations which may oc-
cur in flight. Some data exist indicating that
hyperventilation is associated with:

a. Electrolyte alterations in blood and
tissue,

b. Bronchospasm due to low alveolar CO:
concentration.

c. Cardiac arrhythmias,

d. Central nervous system aberrations.

Since pilots, passengers and any personnel in-
volved in anxiety-producing situations may
hyperventilate, it would seem important to de-
termine the response of a series of subjects to
this event, with special attention devoted to the
possible exaggeration of cardiac or central nerv-
ous system abnormalities with advancing age,
or pre-existing cardiac or pulmonary disease,

Exposure to High Inspired Oxygen Ten-
sions may well occur in pilots of advanced-type
aircraft and in instances where pure oxygen
inhalation is called for by loss of pressuriza-
tion. The effects of exposure to high oxygen
tensions upon body metabolic processes are
poorly understood. However, some data indi-
cate that such exposure can significantly de-
crease mental and physical performance. More
data are required to define the influence of high
oxygen tensions and the critical level of tension
at which decrements in performance may occur.

Eaposure to Low Inspired Oxygen Tension
may also occur in aircraft. Such exposure is
likely to have especially severe consequences in
patients with pre-existing pulmonary disease,


These are considered diagnostic consultations
in internal medicine and are extensive in scope.
A comprehensive cardiovascular review and ex-
amination are therefore an integral part of the
examination.

Laboratory studies supplementing this exam-
ination are blood sugar and serum cholesterol.
Serum triglycerids and phospholipids will be
incorporated as well. Because there is now ex-
perimental evidence to indicate that subjects
with abnormalities in lipid metabolism and
atherosclerosis also have difficulties in handling
carbohydrate, it is planned to do insulin levels
with glucose tolerance tests. The appearance
of a delayed insulin response to a CHO load as
seen in diabetes may be an early clue to the pres-
ence of an accelerated atherosclerosis process,
especially when related to our other aging
parameters.

Special studies are then carried out; these
include electrocardiograms at rest, radiocardio-
grams during exercise, and the conventional
Double Masters test. Vectorcardiograms are
being recorded to supplement this data and to
assess its own merit in regard to early myo-
cardial changes. Studies already completed
suggest that VCG supplies only supplementary
and complementary data and the accumulated
results aro being readied for publication. Other
recently reported results indicate that, using
Mattingly’s criteria, subjects who have abnor-
mal RKG’s during exercise manifest positive
conventional Masters tests. Unsuspected con-
duction disturbances and alterations in rhythm,
however, are often seen on RKG and not on the
conventional resting tracing or Masters trac-
ings. Because the RKG does appear to provide
valuable additional data it forms an integral
part of our evaluation.

Phonocardiography with EKG and with ree-
ords of precordial movements (apex cardio-
gram) is used to provide an objective baseline
in all subjects of ascultatory and palpatory
events. This method also allows sequential com-
parison of these events and documents murmurs
and extra heart sounds. For example, Gallop
Rhythm has been interpreted in older individ-
uals as abnormal. We are currently assessing
this statistically in normals and correlating its
appearance and frequency with our other evi-

dence, to determine its significance and its value
ag an indicator of aging.

Because of our requirements for indirect
methods of assessing myocardial function we
are also attempting to devise, standardize, and
quantitate conventional and new methods for
indirect assessment of the heart. This latter
program utilizes patients with known heart dis-
ease who undergo conventional cardiac catheter-
ization and in whom an opportunity is there-
fore present to simultaneously record and relate
internal and external circulatory events.

Ballistocardiographic changes with age have
been known to occur. A much-improved system
for recording the ballistocardiogram has grad-
ually evolved and the superiority of this new
“ultra-low frequency” (ULF) BCG method is
conceded by the leaders in this field, both in this
country and elsewhere. Its physical require-
ments are not critical and it readily lends itself
to standardization and calibration. Justifiable
dissatisfaction and confusing multiplicity of
older, technically inferior BOG techniques have
made capable investigators and research groups
reluctant to attempt a reappraisal of this whole
area with the newer method until convincing
proof of its value was demonstrated. This atti-
tude and the lack of a suitable, commercially
available instrument have greatly hindered
progress in this field at a time when physiologic
and biophysical studies are providing strong
evidence of the ultimate potential value of this
technique in clinical medicine. The method
clearly deserves a careful, clinical reappraisal.
It is a well-documented fact that in most pa-
tients with overt cardiovascular disease the bal-
listocardiogram is abnormal in waveform.
Furthermore, studies have shown it to be abnor-
mal in about 80 percent of subjects with definite
coronary artery disease; and in a considerable
number of these, the ballistocardiogram pro-
vided the only evidence of abnormality.

One of the most promising areas for research.
in ballistocardiography has been that dealing
with the association of the ballistocardiogram
and age. Past experience has revealed that in
normal persons the amplitude of the ballisto-
cardiogram progressively declines with increas-
ing age from 20 to 40 years, but waveform or
“pattern” remains relatively normal over this



tudinal or long-range observation of his per-
formance capability. Coincident with such an
evaluation, there must be an evaluation of the
pathological changes which have presented
themselves with the passage of time, in relation
to the individual’s physiological capability.
Depending upon the basic requirements of the
man to perform a specific task, we know that
certain physiological alterations and patho-
logical changes per se do not interfere with per-
formance. However, the significance of such
changes in relation to the total performance of
the man must be determined to give him a fair
consideration.

The subjects for these studies have been se-
lected from aviation personnel. A relatively
gross screening was accomplished by limiting
the subjects examined to those who require air-
man’s certification. Inasmuch as there are sev-
eral groups of aviation personnel whose basic
tasks are significantly different but all of whom
are required by Jaw to carry airman’s certi-
fication, data are analyzed in relation to a
specific work category. Thus, factors ulti-
mately identified as contributing to an accel-
erated aging process will be considered in the
light of the part they may play in the man’s
specific work category. To satisfy the statis-
tical requirements of a randomly selected group
of subjects, personnel submit themselves for
the experimental test battery. This includes
all of the examinations required for the issu-
ance of an airman’s certificate in addition to the
many studies performed in conjunction with
the research of their physiological appraisal.
Only information required by current physical
standards is forwarded to the Certification Divi-
sion and serves as the basis for the airman’s
certification, The remainder of the informa-
tion is analyzed and stored for use in research
projects. Statistically significant numbers
have been selected for each 10-year age group;
these subjects are examined annually and dec-
rements noted with the passage of time, so
that ultimately a profile for each individual
will be determined. Subsequently, changes in
this profile will be correlated with the man’s
performance capability.

The study of the effect of the aging process
in aviation personnel and the assessment of

pathology as it may affect the performance of
aviation personnel, are currently being under-
taken in the various laboratories of the Insti-
tute. A brief description of the work being
pursued in the individual laboratories follows.

CARDIOVASCULAR LABORATORY

It is important to reemphasize the dearth of
knowledge concerning the circulatory adapta-
tions to age. Circulatory diseases are foremost
causes of death at the present time and represent
@ major cause of morbidity. Recent evidence
also indicates that younger segments of the
population are victims of these diseases, and in
fact, atherosclerosis has been shown to be a uni-
versal finding in the adult American male. The
clinical manifestations of this change are most
common after 40 years of age with almost
exponential frequency each decade thereafter.
The years after 40 are the fruitful years—the
time when learning has been tempered with
experience, the time of an individual’s greatest
productivity.

The loss of these trained individuals repre-
sents to the community a major economic drain
and causes social consequences that can be as
catastrophic as the initial clinical manifesta-
tions of the disease process. For those of us
in aviation medicine the implications of such
losses are all too visible. Also apparent is the
need for definitive, scientifically sound knowl-
edge of the alterations in circulatory capacity
with time which can serve as a basis for detect-
ing early significant changes which represent a
hazard to personal and public safety, i in the
citizen’s role as aviator.

A.major consideration in the design of the
studies has been methodology. The subjects to
be participants in the projects are healthy avia-
tion personnel; and the studies, while requiring
a high degree of precision, must therefore be
adaptable to outpatients. In addition, the usual
type of hemodynamic studies which require in-
travascular techniques are not acceptable for
this subject population.

For these reasons the following generally ac-
cepted and widely employed techniques have
been incorporated in the series of studies on
each subject. The general protocol includes a
complete history and medical examination.


reproducible or sensitive, are not likely to prove
completely satisfactory. The functional re-
serve of the respiratory apparatus is so large
that resting abnormalities are, in reality, in-
dicative of rather far-advanced disorders.
Studies of this reserve capacity would appear
to be essential if we are to detect age-related
decrements, since such decrements are likely
to be expressed primarily as a loss of functional
reserve.

Therefore, studies of pulmonary function
which will achieve the objectives of this project
must include observations made upon the sub-
ject during various forms of stress, as well as
the usual basal, resting type of observations.

The choice of tests which will provide the
type of data sought must be arbitrary at the
outset, since data permitting definite selection
are not currently available. The situation re-
quires, therefore, that a rather wide spectrum
of tests be investigated from which final selec-
tion of a suitable test battery can be made.
Literature review and experience suggests that
each of the following parameters warrants
consideration :

1. Statice Lung Volwmes.—Vital Capacity,
Residual Volume, Total Lung Capacity. Data
exist indicating that there is a definite relation-
ship between chronologic age and the vital
capacity (VC) and residual volume (RV).
The VC decreases and the RV increases with
age.

2. Dynamie Lung Volumes. — Maximum
Breathing Capacity, Timed Vital Capacity,
Mid-expiratory Flow Rates, etc. Prior studies
have indicated there is a definite age-related
decling in these measures of expiratory flow
rate.

3. “Diffusion Capacity”—The studies of
Bates and others have indicated that the diffus-
ing capacity for oxygen and carbon monoxide
(DO, and Deo) both decline with age.

4. Distribution of Inspired Air—With the
lmown age-related alterations in the thoracic
cage and pulmonary structure it is likely that
an age-related distribution abnormality exists—
the same can be said of measurements of the
mechanics of breathing ; i.e., that the total work
of breathing and its subdivisions will increase
with age.

5. The Respiratory Responsiveness to Altera-
tions CO:, 0. and pH, and to Ewercise—There
is little information as to the relationship be-
tween age and the respiratory response to vari-
ous stimuli, This is a complex relationship, of
course, in which the central nervous system is
intimately involved. Since the speed and ade-
quacy with which the respiratory apparatus
responds to various stimuli is of considerable
importance in aerospace problems particularly,
this is an area which deserves further explora-
tion. Data of this type is not obtained by “rou-
tine” pulmonary function testing; yet, it may
be a critical determinent of functional integrity
under certain circumstances (¢.g., the sudden
loss of pressurization at high altitudes).

6. The Arterial Blood Gases at Rest and Dur-
ing Ewercise—As mentioned above, arterial O2
and CO, tension and pH ultimately are altered
by pulmonary functional impairment. Often,
blood gas abnormalities are absent or minimal
at rest and can be disclosed only by an exercise
test. Occasionally, study of arterial blood gases,
particularly during exercise, will detect an
abnormality which is not disclosed—or only
suggested by—the other pulmonary function
studies (e.g. some forms of diffusion in-
sufficiency).

7. Pulmonary Hemodynamio Alterations.—
Alteration of pulmonary function frequently
Jeads to deviation in pulmonary hemodynamic
behavior. In some instances, hemodynamic ab-
normalities may precede abnormalities in pul-
monary function detectable by other means
(eg. in primary pulmonary hypertension).
Furthermore, alterations in pulmonary hemo-
dynamic behavior may well correlate with age.
In particular, the capacity of the pulmonary
vascular bed and the ability to lower pulmonary
vascular resistance in response to an increase in
pulmonary blood flow may diminish with age.

8. Oxyhemoglobin Dissociation Curve.—It is
known that the hemoglobin oxygen dissociation
curve is altered in a variety of patients with
variant types (other than A) hemoglobin. It
is not known whether hemoglobin maintains its
biochemical integrity throughout the life span.
Interest, attaches to the possibility that the O.
dissociation curve may alter with age and to
the possibility that hemoglobinopathies which



AM 641

STUDIES ON AGING IN AVIATION PERSONNEL

By ARTHUR E. WENTZ, M.D.
DIRECTOR

Georgetown Clinical Research Institute

Approved by Released by
Arthur E. Wentz, M.D. M. S. White, M.D.
Director, GCRI Federal Air Surgeon
AUGUST 1964

FEDERAL AVIATION AGENCY
Office of Aviation Medicine
Georgetown Clinical Research Institute
Washington, D.C.



In the endocrine field, methodology in some
areas is more satisfactorily developed. This
laboratory is primarily interested in the outflow
from the adrenal cortex and in the gonadal
hormones.

Since the target organs of the endocrine sys-
tem are under the direct control of the trophic
hormones from the anterior lobe of the pitui-
tary gland, it may be interesting to study
changes in the ratio of peripheral blood concen-
tration of various endocrine hormones with age.
It is known that gonadal function changes with
age; and it is to be expected that the stress
mediating mechanisms become less efficient with
age. Whether these differences in function are
due to peripheral changes, changes in the pitui-
tary-adrenal axis or changes in the neural inte-
grating mechanism isnot known.

The second major interest of this laboratory
is to study stress factors in the field of aviation.

It has been established for a number of years
that stressor agents cause hyperplasia of the
adrenal cortex in animals. It is known also that
a hyperplastic adrenal cortex is under the in-
fluence of the ACTH secreted from the anterior
lobe of the pituitary gland. Further, research
has established the fact that the enlargement of
the adrenal cortex in response to stressor agents
can be prevented by the administration of gluco-
corticosteroids to the test animal prior to expos-
ing the animal to the stressor agent. Biochemi-
cally, the response to stressor agents is seen as
an increase in the peripheral blood levels of
17-hydroxycorticosteroids (17-OH Cs).

In view of these findings it seems reasonable
to expect that the adrenal cortex of a person
under stress should be hyperplastic if the work
situation acts asa stressor agent. In such a.case
the kinetic response of the adrenal cortex to a
test dose of ACTH should be different from
that of a normal.

In many pathological states the biochemical
systems of the body undergo changes that may
be objectively measured. Often these biochemi-
cal measurements prove valuable as a primary
criterion of disturbed body function, as in the
case of blood sugar measurements on a diabetic
individual. In this study selected biochemical
determinations are being performed on subjects
being evaluated under other projects of this re-

10

search area. Orientation will be toward clarify-
ing other clinical data by biochemical deter-
minations and toward identifying certain deter-
minations with the greatest value in predicting
performance capabilities.

COAGULATION LABORATORY

The development of intravascular blood clots
can lead to acute disability, as can the appear-
ance of a bleeding tendency. The delicate bal-
ance which maintains blood in its normal fluid
state is known to be altered by a variety of
factors. For example, “stress” has been said
to accelerate clot formation—but also is known
to enhance fibrinalytic activity. Little is
known regarding the effect of hypercapnic
acidosis, hypocapnic alkalosis, hyperoxemia and
hypoxemia upon the status of the blood clotting
mechanism. If these conditions do affect co-
agulation, they may have important bearing
upon thrombotic risk in patients breathing oxy-
gen or subjected to conditions producing hyper-
ventilation or hypoventilation.

Multiple studies have suggested that patients
with atherosclerosis differ from normals with
respect to the speed of coagulation, the degree
of clot-dissolving activity and the level of cer-
tain coagulation factors in the blood. Little is
known regarding the age-relation of such
changes in coagulation. There also have been
studies indicating that the likelihood of clot
formation may be predicted by the finding of
coagulation changes suggesting the presence of
“hypercoagulability.” If these studies can be
validated, they may offer a new approach to the
detection of subjects with atherosclerosis and,
more critically, those in whom the risk of throm-
bosis may be particularly high.

BEHAVIORAL SCIENCES LABORATORY

Recent behavioral studies indicate substantial
decrements in certain aspects of mental and
behavioral functions with age, not only in old
age, but from youth to middle age. The func-
tions most affected involve such factors as speed
of computation and skilled movements, speed
of perception and goodness of short-term mem-
ory, particularly in complex or distracting situ-
ations. Unfortunately, all of this work has


even though such disease might be subclinical
under most circumstances.

The individual with normal pulmonary func-
tion utilizes a certain amount of oxygen in car-
rying out respiratory work. As respiratory
work increases (due to increased ventilation),
the oxygen utilized increases. In patients with
respiratory disease, the oxygen requirement per
unit of respiratory work is in excess of normal.
Measurement of the oxygen utilized/unit respi-
ratory work increase may detect early derange-
ments of pulmonary function and indicate pa-
tients in whom sudden demands for increased
respiratory work will be poorly tolerated.

VISUAL AND AUDITORY LABORATORY

Evaluation of the visual system includes
fundus photography, the resultant colored slides
of which yield information regarding the min-
ute as well as the gross changes of the eye
grounds. Such information relates to the oc-
currence of vascular changes in aging. Use of
a photometer in conjunction with the Fundus
Camera has been used to investigate retinal
metabolism. With an electronic pupillograph,
the dynamic measurement of the pupils, sep-
arately and consensually, is recorded on a strip
chart record. Concurrently, the latency period
of light stimulus to iris response is recorded
on a memory oscilloscope. These pupillary re-
actions activated by both light and sound stim-
uli and directed by the autonomic nervous sys-
tem, are indicative of physiological aging
processes,

Refractive measurements include visual acu-
ity findings (with both Landolt Rings and con-
ventional letter symbols), keratometric read-
ings, retinoscopy, stereopsis, phorias and duc-
tions, and amplitudes of accommodation and
convergence. The tests are performed at 20
feet, intermediate, and near distances.

Visual fields are tested using the multiple
pattern screening method, the perimeter and
the tangent screen.

Intra-ocular pressures are taken by means
of the manual and electronic tonometers.

In addition, critical flicker fusion, dark adap-
tation, brightness contrast sensitivity, color dis-
crimination and span of recognition (tachis-
toscopy) evaluations are made and recorded.

Where indicated, Slit-Lamp study and other
procedures are followed.

Hearing tests include both pulsed and con-
stant pure-tone threshold tests using a Bekesy
audiometer and/or other audiometric equipment
together with a sound chamber. Facilities are
available for studies with and without back-
ground noise, monaurally and binaurally.

PHARMACOLOGY AND
BIOCHEMISTRY LABORATORY

Certain physiological and pathological
changes occurring in the older age groups are
reflected by changes in body chemistry. The
Pharmacology and Biochemistry Laboratory is
interested in making biochemical determinations
of such changes which can be correlated with
clinical and physiological measurements. Sev-
eral areas in such a broad field may be fruitful,
but in this laboratory attention is focused on
blood lipids and cholesterol, and on the endo-
crine products. The development of coronary
disease is thought to be closely related to the
blood lipid and cholesterol levels. These bio-
chemical methods are being developed.

Conventional chemical procedures for meas-
uring plasma lipid fractions are difficult, time-
consuming, and not very reproducible. Also,
these methods require large amounts of starting
material. The gas chromatograph is a rela-
tively new instrument which offers the qualities
of high sensitivity with a high degree of accu-
racy, and precision of measurement. The work,
primarily of Sweeley, Horning, and others, in-
dicates that this instrument is particularly
adaptable to the analysis of cholesterol, triglyc-
erides, fatty acids, and phospholipids. There-
fore, one might expect to be able to do adequate
analytical work with minimal amounts of blood.

Many investigators have reported that an in-
crease in cholesterol and other lipid fractions
js seen in atherosclerotic patients. Probably
because lipid measurements are so difficult to
do, not much data is recorded correlating lipid
fraction with objective measures of cardiovas-
cular function. If the gas chromatographic
measurements prove to be satisfactory it will be
possible for us to attempt such a correlation
using the wave-forms of the ballistocardiogram
and EKG measurements.



age span. However, above the age of 40 there
is a rather striking increase in waveform ab-
normality in clinically normal subjects such
that above the age of 50 approximately 50 per-
cent of these individuals have ballistocardio-
grams that are clearly abnormal. These re-
sults were based on cross-sectional studies and
these age trends are generally similar to those
for the incidence of development of clinical
coronary disease, severity of coronary athero-
sclerosis at autopsy, and frequency of death
due to atherosclerosis and coronary heart dis-
ease. However, it has not been proven that the
abnormal ballistocardograms observed in these
“normal” individuals are a direct consequence
of “subclinical” coronary artery disease, al-
though this remains a good possibility; other
age-related changes, such as decrease in arterial
elasticity, are probably implicated. The sin-
gle most important question involved here is
the clinical significance—both diagnostic and
prognostic—of the age-associated ballistocardi-
ographic abnormalities observed in individuals
considered normal on the basis of studies with
currently available methods, known to be in-
sensitive. This matter assumes even greater
importance since such changes are found in
individuals whose ages make the presence of
anatomical coronary atherosclerosis in some de-
gree a virtual certainty.

One of the best methods for answering this
basic question is to carry out long-range, longi-
tudinal studies on normal airmen in different
age groups with careful clinical followup. If
it could be shown that those individuals whose
ballistocardiograms were abnormal at the out-
set developed cardiovascular disease (and spe-
cifically coronary disease) earlier or more fre-
quently than did those with normal ballisto-
cardiograms, then it would become evident that
ballistocardiography is a remarkably sensitive
method for demonstrating progressive deteri-
oration of circulatory function with increasing
age. Although final proof of this relation has
not been obtained, there is a substantial and
increasing body of evidence which supports it.
Starr’s recently published results representing
a 20-year followup revealed that cardiovascu-
lar disease (and especially coronary heart dis-
ease) had developed with far greater frequency

in those individuals whose original ballisto-
cardiograms were either very small or abnormal
in waveform than in those whose records were
normal. Preliminary results from a similar
study by Scarborough, Baker and others,
though with shorter followup, appear to be
rather similar. Moss, Graybiel, and their asso-
ciates, in studies on Naval aviators, have found.
that the ballistocardiogram provides a means
of detecting “accelerated cardiovascular aging”
in these airmen. Inasmuch as the insidious de-
velopment of advanced circulatory disease
(especially coronary heart disease) in aging avi-
ation personnel is one of the most difficult prob-
Jems that confronts the FAA’s Office of Avia-
tion Medicine, longitudinal and cross-sectional
ballistocardiographic studies on airmen would
seem to be a most promising kind of research
ina critical area.

The Cardiovascular Laboratory is well
equipped to conduct investigations of this kind;
ballistocardiographic instruments of the ultra-
low-frequency type, as well as the older, con-
ventional Starr type, are in routine use for
studies on normal individuals and subjects with
various cardiovascular disease states. To pro-
vide intercorrelations, a variety of other physi-
ologic events (EKG, respiration, heart sounds,
apex cardiograms, arterial pulses, etc.) are re-
corded simultaneously. Acquisition of these
data on magnetic tape, as well as on conven-
tional media, is now in progress and this will
not only permit easy recall of the data in elec-
trical analog form at a later date, but also per-
mit analyses and correlation by computer
methods.

Routine radiographic methods have also been
used thus far; and as indicated by the require-
ment of our subject: population and known ab-
normals in the hospitalized population to which
we have access, coronary arteriography and
other special methods are employed.

Exercise and pharmacologic stress and the
circulatory adaptations to such stress, are being
used to assess overall circulatory capacity.
Astrand, Reeves, Bishop, and others have com-
piled an extensive body of data on isolated
aspects of these adaptations. The value of this
approach is without question, and while our
own information is not yet subject: to analysis,


PREFACE

This report was originally presented at the dedication of the Civil Aero-
medical Research Institute of the Federal Aviation Agency in Oklahoma
City, Okla., on October 20, 1962, It has been brought up to date and
revised to include a more detailed description of work being done in the
individual laboratories of the Georgetown Clinical Research Institute.

Many passages of this paper are contributions from the various members
of the Georgetown Clinical Research Institute staff, in their respective
specialties,

iv


RClo 54
USAY
1964

FOREWORD

‘This publication represents the first report of a new series issued by the
Office of Aviation Medicine, Federal Aviation Agency.

The Office of Aviation Medicine reports will include technical and re-
search reports emanating from the medical divisions in the regions, the
divisions in the Office of Aviation Medicine and the research institutes.
The publishing of reports from the Civil Aeromedical Research Institute,
Oklahoma City, and the Georgetown Clinical Research Institute, Wash-
ington, D.C., under separate institute covers, has been discontinued since
they will be included in this series.

The number of copies available for distribution will be limited. It is
requested that optimum circulation be given to these publications by the
personnel to whom they are sent.

Inquiries regarding the contents and availability of these reports should

be addressed to the Office of Aviation Medicine, Federal Aviation Agency
Headquarters, Washington, D.C., 20553.

Mf Whee

M. S. Wurtz, M.D.,
Federal Air Surgeon.

iii

438





been piecemeal in that behavioral test findings
have not been related to each other or to physi-
ological and clinical findings in a global fash-
jon. The intercorrelation with a broad variety
of carefully chosen behavioral task scores with
elaborate and precise clinical data, should yield
valuable insights into the processes of aging,
ag well as the behavioral implications of certain
physiological findings. Behavioral test pro-
ficiency scores will be especially carefully inter-
related with tests of goodness of visual and
auditory sensory functioning, so as to separate
peripheral from the more central kinds of
deficits.
‘The tests now in use include:

1. Perceptual motor speed tests:
a, Serial, choice reaction-times.
b. Serial stimulus matching reaction-times.

2. The Wechsler Digit symbol substitution
test and the Reitan Trails Making Test, two
brief, well-standardized speed tests which are
good discriminators of age and brain dysfunc-
tion, respectively.

8. Running short-term memory test.

4, Speech intelligibility test for digits, using
unfavorable signal-noise ratios and two degrees
of frequency-band limitation, designed to dis-
criminate between sensory and perceptual
disability.

5. The Halstead Tactual Performance Test
and Wechsler Block Design Tests, both good
indices of organic brain impairment.

6. The Halstead Categories Test, an excel-
lent index of organic brain impairment.

7. Visual flicker-fusion thresholds (CFF)
are measured by the Visual and Auditory
Laboratory.

8. The Cattell 16PF Personality Inventory
is given on the second or later visits.

Groups of older people are almost invariably
slower on the average than groups of younger
people, at almost any psychological test, and
frequently are somewhat poorer also. Much
of this so-called “age decrement” in perform-
ance may be due to cardiovascular disease which
produces cerebrocirculatory insufficiency. If
true, this fact would be of the first importance
in establishing policy in regard to age, health,
and flying.

ii

Results from behavioral tests have already
demonstrated that cardiovascular disease is
statistically associated with some impairment of
mental efficiency. Further statistical correla-
tions will be obtained on a continuing basis, and
special types of cardiovascular cases will be re-
cruited and tested. It is particularly impor-
tant to find sizable numbers of cases of parallel
age range and ranges of severity of disease of
several types, who are on different medical
regimens.

An attempt will be made to assess the nature
of this impairment by comparing test profiles
of cardiovascular disease cases with cases
suffering known kinds of organic brain
impairment.

From the longitudinal studies of various
physiological and behavioral characteristics,
masses of data will be obtained. In order to
extract and identify these elements of diag-
nostic or prognostic significance, these data
must be subjected to sophisticated statistical
analyses. In addition, electronic computer
techniques must be utilized in analysis and in-
terpretation of continuous wave-form data gen-
erated by medical techniques, such as electro-
cardiography and electroencephalography.

BIOPHYSICS AND ELECTRONICS
LABORATORY

Since the solution to current and anticipated
problems in aeromedical research can only be
solved by using a team approach, the Biophy-
sics and Electronics Laboratory plays an inte-
gral part in the multidisciplinary activities of
the Institute. In the development of new tech-
niques and procedures for clinical evaluation
of the functional status of aviation personnel,
experiments are becoming more complex, and
more variables must be accounted for or con-
trolled. In order to delineate physiological
parameters more precisely between individuals,
increased accuracies in measurements are re-
quired. The development of integrated data
handling systems has contributed greatly to the
growing sophistication of research instrumenta-
tion in medicine. As a consequence, the use of
computers has become a necessity, both on-line
and off-line, to analyze measurement results and