CHAMBER
WALL

- NITROGEN ‘

SENSOR

TO PASSENGER mask

OXIMETER
AMPLIFIER

<—_
|

& MONITOR

TO RECORDER

+ exe monitor

L IMPEDANCE
| PNEUMOGRAPH

PRE AMPLIFIER

@ HYPODERMIC NEEDLE -MICROCATHETER SAMPLING ORIFICE— MASK
EAR OXIMETER © ELECTROCARDIOGRAPH LEADS (©) OXYGEN
REGULATOR — DILUTER DEMAND— PRESSURE BREATHING A-14

© IMPEDANCE PNEUMOGRAPH LEADS

‘IGURE 2.
altitude of 14,000 feet.

apidly donned the Sierra passenger mask
Figure 3). Each subject wore a new mask;
qs six masks were used in this evaluation.
‘he flow of oxygen to the mask was regulated
y an altitude-sensitive regulator of the type
sed in multi-passenger oxygen systems of trans-
ort aircraft. The flow from this regulator,
istead of being transmitted directly to the sub-
set, was first routed outside the chamber through
flowmeter and needle-valve arrangement in
rder to obtain precise measurement and control
Ef the flow (Figure 3). Excess oxygen as ‘pro-
ided by the regulator was vented outboard out-
de the chamber.
The subject exercised for three minutes at each
titude and rested during the climb to each
vcessive higher altitude level. The chamber
as leveled off at 14,000, 21,500, 29,000, 35,000
id 40,000 feet and readings were taken pre-
sercise, during the first minute and last minute
* exercise followed by post-exercise recordings

Instrumentation of subjects prior to nitrogen washout and determination of minute volume at an
Subject wearing a crew-type mask.

at 14,000, 21,500, 29,000, 35,000 and 40,000 feet.
Motion pictures were taken of the subjects dur-
ing the maximum altitude portions of the flights
and closed-circuit television was used to monitor
the subjects at all times,

Mask Efficiency. Two Custom Engineering
and Development Company Model 300 AR
Nitralyzers were used to continuously measure
the mask nitrogen. These instruments exhibit
an initial response latency of 0.024 second, 90%
response being obtained in 0.044 second. A
vacuum pump, regulated to 0.6 mm, set the
sampling rate at 3 ce per minute. The contin-
uous sample was drawn through a needle valve
and microcatheter tubing (PE 60) of 0.030 inch
internal diameter. The small, extremely light-
weight, microcatheter tubing connected to the
mask did not require extensive modification of
the mask nor did it add significant weight; thus,
fit and operational characteristics of the mask
were not compromised.



1

t

I
RESPIRATION

|
|
|
|

i
HEART RATE

OXIMETER'

77

1
i
1
I
l
f
v
!
I
I
I
t
i
1
1
1

I
|
|
|
ALTITUDE ! 40,000 FT.
4 |
STOP EXERCISE H
| |
EXERCISE RESTING |
I I
I I
170 180 190 200
TIME -SECONOS
Ficure 9. Sample. Physiograph recording showing

rapid blood oxygen re-saturation following cessation
of exercise at 40,000 feet. Subject No, 2.

cated a relatively low blood oxygen saturation
(without a commensurate lowering of tracheal
oxygen partial pressure) at the end of the third
minute at 29, 35, and 40 thousand feet. Rapid
recovery of blood saturation following cessation
of exercise is shown in a sample recording from
this subject (Figure 9). This subject did not
exhibit a marked change in respiration when
compared to the 14,000-foot baselines; however,
he exhibited one of the most consistently elevated
heart rates during exercise at 85 and 40 thousand
feet, which may be indicative of his response to
hypoxic stress, state of physical condition, or
both.

IV. Discussion

The National Aerospace Standard (NAS)
recognizes gas analysis and blood-oxygen-satura-
tion determination as the two principal alternate
methods to be used in altitude-chamber evalua-
tions of passenger masks.

In this study, the experiments were designed
to measure both of these variables simultaneously.

Exercise time at altitude was held to a mir
mum in order to minimize the probability
bends and to reduce fatigue.

Previously, high altitide evaluations of p
senger masks have been carried out on resti
subjects. In some evaluations, a brief episc
of voluntary hyperventilation took place to
crease minute volumes to 30 liters/minute. T
procedure is recommended in NAS 1179, but
is practically impossible for a sedentary subj
to maintain this level of respiration for m
than 30 to 45 seconds without experiencing sev
symptoms of hypocapnia (dizziness, paraesthe:
muscular cramps, etc.).

In addition, voluntary hyperventilation
duces the alveolar and blood carbon diox
partial pressures by the washout effect. By
mere physical reduction of the carbon diox
partial pressure, an increase in alveolar oxy.
partial pressure is induced. As pointed
previously, this physiologically unsteady st
may be maintained for only brief peri
Changes in blood chemistry and cerebral bl
flow induced by voluntary hyperventilation :
detract from its usefulness in mask evaluati

A controlled and measured work load
used in these experiments to stimulate resp
tion to the 30 liters/minute standard witl
imposing severe changes in respiratory
blood-gas composition.

Admittedly, increased work load produces
increase in oxygen consumption. The leve.
work load used in these experiments should
duce an increase in oxygen consumption of
proximately .35 to .50 liters/minute above
resting value.?”

Neither voluntary hyperventilation nor e
cise is entirely a satisfactory means of eleva
the minute volume; voluntary hyperventila
tends to over-estimate the physiological effec
ness of a mask, and exercise tends to un
estimate this value. The use of exercise, how
increases the margin of safety and assur
that an adequate blood oxygen saturation
be maintained during periods of increased
piration.

One disadvantage of using exercise in 1
evaluations at altitude is the increased susc
bility to the development of bends. The de
of denitrogenation, altitude profile, and expc
time must be carefully considered in relatic
the use of exercise.


misleading, increase in CO, production and an
R.Q. greater than 1.0. Conversely, hypoventila-
tion and retention of CO, indicate an apparent,
but misleading, decrease in CO; production re-
sulting in a decreased R.Q. which may be less
than 0.7.

One must keep in mind that in a steady state
condition the unequal exchange of oxygen and
carbon dioxide involves only that portion of the
gases consumed and produced. For example, if
during a one-minute period at rest 0.3 liters of
O, were consumed and 0,25 liters of CO, were
produced (R.Q.=0.83), the resultant volumetric
difference of 0.05 liters in the seven or eight
liters passing through the lungs during this one
minute would be relatively small, and the error
(only a few per cent) would be well within the
experimental error of the determinations of end
expiratory nitrogen.

All of the nitrogen which dilutes the inspired
gas originates from air by mask leakage or
dilution-valve activation with the exception of
that derived from the tissues; after six to eight
minutes of breathing oxygen under a steady
state condition this constitutes less than one per
cent of the lung volume.

Using calculations suggested by Luft,’ the
admixture of air can be determined; ie.:

Admixture of air _ Inspired nitrogen fraction

100 Nitrogen fraction of air

By substituting end expiratory nitrogen for
inspired nitrogen:

End expiratory _nitrogen_

Admixture of air=Nitrogen fraction of air

100

Using these formulas, the percentage of dilu-
tion, supply oxygen, oxygen from the ambient
air, and total oxygen may be derived according
to the following calculations:

End expired N- x 100

2 of air (79.08)

% Oxygen from Supply=100%—9% dilution
Oxygen from Ambient

Per Cent Dilution=

=Per cent dilution x oxygen
contained in ambient air.

Total oxygen=oxygen from supply++oxygen from am-

bient air.
Calculated inspired oxygen partial pressure=(Pn—47)
x Per cent
total O:.
Where: Pa=Total pressure in mm Hg at ambient
altitude.

47=Pressure, in mm Hg, of saturated water
vapor at body temperature.

Ill. Results

The oxygen flow of the passenger mask NTPD
(normal temperature pressure dry, 70° F.—760
mm-dry) and BIPS (body temperature pressure
saturated, 37° C.—ambient—saturated) is shown
in Figure 4. The flow to Subject 5 was increased
at 29,000 and 35,000 feet during exercise due to
a precipitous fall in blood oxygen saturation.
Flows to the remaining subjects were adjusted
to the minimal values, according to FAR Part
25.

30°
zal ALTITUDE NTPD. BPS
eb 215 1.02.85 °
z 29 1837.73
2r 35 258 18.62
Zeal 40 3.10 26.37
© sol 35 3.10 18,76
a 29 2.58 10.90 °
2 18- '
WileP }
aap
BTPS
= of 9
z 7 © Flow increased !
oS er Subject No. 5 oO
Xe
lo}
ab NTPO Q
° x
L __——
2 —
1 i 1 L i
10 14 2.5 29 35 4.0
ALTITUDE (Thousand Feet)
/
Figure 4. Oxygen flow rate.
Heart Rate. Predictably, the mean heart

rates increased with exercise, this being more
pronounced in the third minute of exercise.
There was also an over-all increase in mean
heart rate with increase in altitude (Figure 5).
These latter increases at similar exercise levels
may have been partially due to subject appre-
hension with increase in altitude; however, the
main stimulus appears to, be hypoxic stress as
indicated by lower blood oxygen saturations and
lower oxygen partial pressures at the higher
altitudes (Figures 6 and 7). At 40,000 feet, the
average tracheal oxygen partial pressure dropped
from 86.4 mm Hg at the end of the first minute
to 77.2 at the end of the third minute (Figure
7). A typical nitralyzer record is shown in
Figure 8. The oximeter earpiece used on Subject



ROBERTSHAW 0C-9
REGULATOR

CHAMBER
WALL

PASSENGER FLOW
CONTROL UNIT

1

Og SUPPLY

¢ L_-

FLOWMETER

MERCURY
MANOMETER

NEEOLE
VALVE

ry
LU,
NITROGEN Pe]

OXIMETER
AMPLIFIER
@ MONITOR

NEEDLE
VALVE

TO RECORDER:

EKG MONITOR

IMPEDANCE
|_PNEUMOGRAPH
PRE AMPLIFIER

Ficure 3.
volumes.
sure control regulator within the chamber through

was reduced to standard conditions and returned to the mask.

overboard.

In the evaluation of oxygen mask efficiency,
one of the most important measurements is that
of the partial pressures of inspired gases. A
continuous flow mask, while worn by a human
subject, defies direct measurement of these pa-
rameters (without compromise of mask perform-
ance) due to the rapid changes in gas composition
at the facepiece. The percentage of gases in the
facepiece of the mask may be averaged by an
integrating reservoir; this average indicates a
trend, but is influenced by the inactive gases of
the facepiece and anatomical dead space. In
order to estimate the composition of inspired
gases an indirect approach was used; this tech-
nique is based on the assumption that the end-
expiratory gases are completely mixed and have
equilibrated with the blood in the alveoli.

Nitrogen is not involved in metabolic ex-
change. If the absorption of O, and the produc-

@ HYPODERMIC NEEOLE ~ MICROCATHETER SAMPLING -MASK
@® EAR OXIMETER ©) ELECTROCARDIOGRAPH ©) IMPEDANCE
PNEUMOGRAPH LEADS

Instrumentation of subjects following completion of nitrogen washout and determination of minu
Subject has completed passenger mask-donning.

Oxygen flow to the mask was routed from a pre
the passenger flow orifices outside the chamber where
Excess oxygen from the regulator was dumpt

tion of CO, were exactly the same, the amow
of nitrogen inspired would equal the amou:
expired; i.e., nitrogen molecules inspired =nitr
gen molecules expired. The metabolic respir
tory quotient (R.Q.) would equal one. Howeve

CO, produced
O, consumed

normally equal to one, or unity. Under the
conditions there may be a relative difference
the nitrogen composition of inspired and expir
gases. The metabolic R.Q. depends upon t
predominance of carbohydrates (1.0), prote
(0.82), or fat (0.71) being metabolized and
usually about 0.83. The respiratory R.Q. m
vary temporarily from the metabolic R.Q. d
ing unsteady states such as hyperventilatic
The increased lung ventilation produces a blo
off of CO, from the blood with an apparent, I

the metabolic R.Q.= and isn


S) a)
8 8
7 7
* /\ AA ih Apt °
4
EXERCISING
3 3
START EXERCISE
12 +2
ke 30 SEconps ———_________
tl ll

cre 8. Nitralyzer record of Subject No. 4 at 29,000 feet.
Numbers 0-1.0 equal 0-100% nitrogen subject to calibration correction.
ve should not be confused with flow, volume or mechanics of respiration. (1)
(3) Continuing.

ed PrO; due to exercise.

rvoir, (2) Dilution valve activated.
End expiratory nitrogen concentration.

Yeygen Partial Pressure. The tracheal oxy-
partial pressure remained above 83.8 mm Hg
ul subjects under all conditions of altitude for
first minute of exercise except for Subject
5, who experienced a drop in PrO.
71 mm Hg at the end of the first
ute of exercise at 40,000 feet. In the third
st) minute of exercise, the PrO, of this sub-
dropped to 70, 71, and 64 mm Hg at altitudes
29, 35, and 40 thousand feet, respectively. To
t the precipitous drop in P;O, and blood
gen saturation at 35,000 feet, the flow was
eased from 2.58 Ipm to 3.10 Ipm; the post-
‘cise P7O, climbed to 93 mm Hg and 99%.
vid recovery after 114 minutes of exercise, in
ch the PO, and blood oxygen saturation
oped to 64 mm Hg and 80%, was accom-
aed at 40,000 feet by merely discontinuing
‘cise; this produced a rapid climb in P,O,
blood oxygen saturation to 93 mm Hg at
»
espiration. Subject No. 5 was the oldest (age
and the largest (225 lbs.) of the subjects used

Slope of line indicates increased dilution and re-
Nitrogen
Inspiration of oxygen from
(4) Oxygen, inspired primarily at (1) above, exhaled.

in this series of experiments. His larger body
surface area undoubtedly increased his oxygen
consumption in comparison to the other subjects.
He exhibited marked increases in respiratory rate
from 14 respirations per minute at 14,000 feet
(at which time the baseline minute volume was
determined) to 24, 25 and 24, respectively, at
29, 85 and 40 thousand feet. A crude estimate
of this effect may be made by assuming that the
baseline tidal volume (determined during exer-
cise at 14,000 feet) remained constant (1,857 cc)
during subsequent ascent to higher altitudes.
The indicated increase in respiratory rate would,
therefore, increase the baseline minute volume
from 26 lpm (BTPS) at 14,000 feet to 44.6 Ipm
at 29,000 and 40,000 feet, and 46.4 Ipm at 35,000
feet, an overall minute volume increase of 48%
to 54% above the specified Ipm. With these
conditions prevailing, the basic design criterion
of the mask is exceeded by approximately 50%.

Subject No. 2 exhibited satisfactory P,O, and
blood oxygen saturation levels at the end of the
first minute of exercise; however, oximetry indi-



TECHNICAL REPORT STANDARD TITLE PAGE
T. Report No. 2. Government Accession No. 3. Recipient's Catalog No.

FAA~AM-72-10

al

Title and Subtitle 5. Report Date
PHYSIOLOGICAL EVALUATION OF A MODIFIED JET TRANSPORT March 1972
PASSENGER OXYGEN MASK

6. Performing Organization Code

7 Rather's) 8. Performing Organization Report No.

Ernest B. McFadden, M.S.

9, Pertorming Organization Name and Address 10. Work Unit No.
FAA Civil Aeromedical Institute
P. 0. Box 25082 TT. Contract or Grant No.

Oklahoma City, Oklahoma 73125

13. Type of Report and Period Covered

12. Sponsoring Agency Name ond Address

Office of Aviation Medicine OAM Report
Federal Aviation Administration
800 Independence Avenue, S.W. 1. Sponsoring Agency Code

Washington, D.C. 20591
Supplementary Notes

Research leading to preparation of this report was performed under Project
No. AM-A-69-PRS-13.

& Absvact THis paper describes altitude chamber experiments conducted with human sup=
eects using a new continuous-flow disposable passenger mask applicable for emergency
se to maximum altitudes of 41,000 feet. This mask design differs in configuration
com the previous omni-directional maska designed to meet the requirements of National
srospace Standard 1179 and FAA Technical Standard Order C-64 in that the inner face
lap or seal has been eliminated and the cylindrical shape reduced to a modified

one. The primary goal of this study was to determine if design modification of the
ask induced an increase or decrease in physiological efficiency. Of paramount con-
2mm was the possibility that modification of the configuration and facial seal might
icrease the leakage rate of ambient air into the mask, and thereby compromise its
vility to provide the level of protection required at the maximum altitude of the
reraft, Subjects were instrumented to obtain a variety of physiological data.

is included EKG impedance pneumograph, ear oximetry, and expiratory nitrogen, and
mute volume. The continuous flow of oxygen delivered to the passenger mask was
mtrolled and precisely measured. The mask was evaluated at altitudes of 14,000
.,500, 29,000, 35,000 and 40,000 feet. The average inspired tracheal oxygen partial
‘essure remained above 83.8 mm Hg under all conditions of rest and exercise at all
titudes except for the third and last minute of exercise at 40,000 feet. If a
iderate degree of physical activity is to be maintained for more than a few minutes,
tygen-flow rates should be increased commensurate with the anticipated level of
tivity. Larger subjects with increased body surface areas exhibit lower blood
ygen saturations and tracheal oxygen partial pressures at a standardized oxygen

ow due to increased oxygen consumption.

. Key Words 18, Distribution Statement
ygen masks, decompression, hypoxia, Availability is unlimited. Document may
otection, altitude, passengers be released to the National Technical

Information Service, Springfield,
Virginia 22151, for sale to the public.

v Security Classif, (of this report) 20. Security Classif, (of this page) i No, of Pages | 22, Price

Unclassified Unclassified iL $3.00
‘m DOT F 1700.7 (8-69)



feet, and again fluctuated to a marked degree at
40,000 feet on oxygen. It appeared that this
“hunting” phenomenon was more marked when
some degree of hypoxia was present. In general,
the ear-oximeter readings appeared to be more
stable during exercise than at rest.

Maintenance of an adequate blood-oxygen
saturation is the desired end result. Instrumen-
tation artifacts and variations in the physiologi-
cal response of the mask-wearer may result in
considerable variation in the ear-oximetry indi-
cations of blood-oxygen saturation.

The function of the mask is to deliver sufficient
oxygen to produce an adequate tracheal oxygen
partial pressure. Since pressure breathing is
not involved in passenger systems, the mask can-
not provide partial pressures in excess of those
provided by a 100% concentration of oxygen.
A hypothetical leak-free passenger mask, cap-
able of delivering undiluted 100% oxygen to the
alveoli throughout inspiration would therefore
exhibit maximum efficiency. The resulting oxy-
gen partial pressure, therefore, becomes merely
a function of the ambient barometric pressure
minus the vapor pressure of saturated gas in-
spired, ie.: (Pp—47).

It should be pointed out that a discrepancy
exists between the performance of any oxygen
equipment evaluated at constant altitude, as pre-
sented in this report, and the dynamic changes
which occur during rapid decompression. Ex-
periments have been conducted in this area by
Bryan and Donaldson,*** but are beyond the
scope of this report.

V. Conclusions

1. The average inspired tracheal oxygen par-
tial pressure remained above 83.8 mm Hg under
all conditions of rest and exercise at all altitudes
except for the third (last) minute of exercise at
40,000 feet.

2. The average blood oxygen saturation during
exercise remained above the 14,000-foot air
breathing baseline (90.8%) during the first

10

minute of exercise except at an altitude of 40,0C
feet where it dropped to 89.6%.

3. Following three minutes of exercise, mea
blood oxygen saturation dropped below th
14,000-foot air breathing control baselines at a
altitudes by differences of 0.7, 4.8, 5.9, and 6
per cent at 21.5, 29, 35 and 40 thousand fee
respectively.

4, The average respiratory rate at the max
mum altitude increased 20% during the fir
minute of exercise, and 37% during the la
minute of exercise when compared to baseli
minute volumes determined at 14,000 feet breat
ing 100% oxygen. Providing tidal volumes 1
mained constant, the mean volumes wou
approximate 28,8 to 32.8 litersminute. The
were large individual variations, however, wi
the 30 Ipm minute volume requirements of TS
C-64 being exceeded by as much as 50%.

5. As in previous evaluations“ larger st
jects with increased body surface area exhibit
lower blood oxygen saturations and tracheal p:
tial pressures at a standardized oxygen flow ¢
to increased oxygen consumption.

6. An ideal technique for increasing the r
piratory minute volume to the levels specified
NAS-1179 and TSO C-64 is not readily atta
able. Originally formulated by general conc:
sus of a number of physiologists, physicians, a
engineers, these levels are representative of
anticipated minute volume that a naive pass
ger would exhibit during the excitement of
aircraft rapid decompression.

7. Voluntary hyperventilation leads to
overestimation of the efficiency of a mask desi
whereas evaluation during exercise undere
mates mask efficiency within the framework +
intent of NAS 1179 and the Federal Aviat
Regulations.

8. If a moderate degree of physical activ
is to be maintained for more than a few minu
oxygen flow rates should be increased ¢
mensurate with the anticipated level of activ


The increased minute and tidal volumes de-
eloped during exercise impose efficiency require-
jents of mask performance in excess of similar
valuations conducted on the sedentary, resting
ubject.

At 40,000 feet, 3.1 liters/minute NTPD equals
6.4 liters/minute BTPS. A subject breathing
0 liters/minute will empty the reservoir bag and
raw in air through the ambient air valve. The
verage composition of inspired gas is shown in
‘igure 10.

If, however, there are significant and uncon-
trolled openings around the periphery of the
mask, ambient air may be drawn through these
during peak inspiration rather than through the
check valve of the reservoir bag.

The ear-oximeter determinations exhibit some
degree of variability, depending upon physical
activity and subject movement. Fluctuation of
the ear oximeter was pronounced during resting
and air breathing at 14,000 feet, became more
stable with 100% oxygen and exercise at 14,000

100
90Fr S
80
Q 70F
©
w
© 60F
oa
2 50r
we
S 40
b
ai
WwW 30
a
a 20
10
ie)
ACTIVITY] RP IE LE RA| RP IE LE RA| RP IE LE RA|RP IE LE RA
ALTITUDE 21,500 29,000 35,000 40,000
7.
[7] 0, DERIVED FROM AMBIENT RP — RESTING PRIOR TO EXERCISE
i] 0, vERIVeD FROM SUPPLY 1E — FIRST MINUTE OF EXERCISE
LE — LAST MINUTE OF EXERCISE
[J OTHER DILUTING GASES RA — RESTING AFTER EXERCISE

jure 10, Histogram showing dilution of inspired gas with ambient air as calculated from the end expiratory
nitrogen concentrations.

9



Ex. 100% Op (Crew Mask)

HEART RATE,
8
T

90+
eob
Rest Air © After | min. Exercise
Toh X Lost min, Exercise
sob © Rest Og
@ Exercise Og
50 NeS

cn hit OO

100 % Op (Crew Mask)
° on L n n J
lo 14 ais 29 35004

ALTITUDE (Thousand Feet)

RESPIRATION
w
8
T

Ficure 5. Average heart and respiratory rates. Note
the increase in heart rate from the first to the last
minute of exercise at altitude.

No. 1 appeared erratic and unstable with read-
ings, for example, of 90% blood saturation while
breathing 100% oxygen at 14,000 feet. The ear-
piece and amplifier were replaced. The average
blood oxygen saturation dropped to its minimum
value at the end of three minutes of exercise at
40,000 feet (83.6%); however, re-saturation to
an average of 90.8% occurred within a short
period of time (30-45 seconds) following cessa-
tion of exercise (Figure 6).

Blood Oxygen Saturation. The National Aero-
space Standard states that blood oxygen satura-
tion baselines established at 10,000 and 14,000
feet should be obtained with the subject engaged
at the same level of activity as during the eval-
uation at higher altitudes. Comparison as the
mean blood oxygen saturation of the subjects at
rest breathing air at 14,000 feet (93.8%) to that
at the last minute of exercise (89.9%) indicates
a difference of 3.9% which agrees with results
obtained in a previous study.® Average blood
oxygen saturation levels prior to exercise ex-
ceeded the resting baseline (93.8%) at all alti-
tudes. Post-exercise saturations were 1.3% to
4.6% lower than the above baselines.

Nz Washout 100% O2 (Crew Mask)
Q
90F

'Y Resting Pre Exercise
sob © Resting Post Exercise
© After Imin, Exercise
40r x After 3 min. Exercise

30h N=6

PER CENT BLOOD OXYGEN SATURATION
8
T

20+

an
° 14 Ll 4 1 fl

1014 215 29 35 40

ALTITUDE (Thousand Feet)

Ficure 6. Average blood oxygen saturation as deter
mined by ear oximetry. Note the decrease in bloo¢
oxygen saturation from the first to the third minute
of exercise.

160 Np Washout 100% Op (Crew mask)
150 > on Passenger Mask
40 F i
| \
130+ Hl
1
20 + |
nob \
Wook
Py A
fp 90F
mm Hg 80> LO
70> Air Breathing Basetines
60+
SOF & Resting Pre Exercise
40 Ol Resting Post Exercise
| © After I min. Exercise
30 x After 3 min. Exercise
zo Nes
tof
° 14 f 1 1 ,
014 215 2 288

ALTITUDE (Thousand Feet)

Ficure 7. Average inspired oxygen partial pressure
The air breathing baseline at 10,000 and 14,000 fe
is merely a function of barometric pressure; i¢
(Ps-47) x 20.94% and is identical irrespective «
physical activity. The combination of a crew mas
and breathing 100% oxygen at 14,000 feet caus:
the inspired tracheal oxygen partial pressure to ¢
off scale to a calculated value of approximate
400 mm Hg.


With the introduction of jet-transport pas-
senger aircraft certified to operate at high alti-
tudes, new oxygen systems and masks were
designed and evaluated.?* Subsequently, stand-
ards for passenger oxygen masks were compiled
and published. The National Aerospace Stand-
ard 1179* and Federal Aviation Administration
Technical Standard Order (TSO) C-64* set
forth manufacturing, material, and testing
standards for passenger oxygen masks.

An excellent description of the basic phys-
iological rationale of oxygen equipment design
for aircraft has been prepared by the SAE
A-10, Aircraft Oxygen Equipment Committee.°
An additional report delineates the basic criteria
and design philosophy of jet transport passenger
oxygen systems.’

II. Methods

Procedure. The altitude chamber flight pro-
file is shown in Figure 1. Six subjects who had
received altitude indoctrination within the past

PASSENGER MASK EVALUATION

404
CHAMBER {Per FAA TSO-C64
PROFILE: Per. NAS II79
35
30
gz
= 254
5
3
220 mv.tv
= BASELINE
S| o, eascune |
S15
5
a

S

DON CREW MASK

T T T T t
io) 10 20 30 40 50 60
TIME (minutes)

Ficure 1. Altitude chamber profile used in evaluation
of the Sierra 239-601 series prototype disposable
passenger oxygen mask.

two years were employed. Instrumentation i
shown in Figures 2 and 3. The mask was no
donned until after air-breathing baselines wer
established at 10,000 and 14,000 feet. A safet:
observer accompanied each subject.

A Waters ear oximeter, Model XE 350, wa
affixed to the antihelix of the subject’s ear 10 t
15 minutes prior to the chamber flight, to allov
stabilization. The output of the earpiece wa
fed into an XE-350 oximeter and continuous!
recorded on a Physiograph. The latter was als
used to record signals from EKG electrodes an
the output from impedance pneumograph ele
trodes attached to the subjects. The impedanc
pneumograph was included in the experimer
to attempt to determine if changes in the re
piratory activity baseline occurred during sul
sequent ascent to altitude, At the present tin
there is no satisfactory method of measurir
respiratory volumes and activity while wearir
a passenger mask without compromising tl
performance of the mask.

After a preliminary assurance of the subjec’
capability to equalize ear pressures, the subje
rested quietly at 10,000 feet until the ear oximet
reading indicated a stabilization of blood oxyg
saturation. Then the subject was depressuriz
to 14,000 feet to establish similar resting a
exercise baselines at this altitude.

When it appeared the blood saturation w
stabilized at 14,000 feet, the subject donned
crew-type demand oxygen mask and commenc
breathing 100% oxygen. Immediately followi
crew-mask donning, exercise on a bicycle ergo
eter (modified so that it could be operated
each subject while seated in a passenger ty
aircraft seat) was initiated. The exercise le
was set at 45 rpm (speed) and 45 watts (loa
to obtain the desired respiratory activity (¢
proximately 25 to 30 liters/minute). This
regarded as a light to moderate work load ¢
proximately equivalent to walking at 3.0 to
mph.

Exercise was continued until the desired m
ute volume, as indicated by a dry gas meter, ¥
obtained and stabilized. The subjects beca
denitrogenated during this period, thereby
ducing the possibility of bends with exercise
the subsequent higher altitudes.

After completion of nitrogen washout at 14,
feet, the subject removed the crew mask ¢


PHYSIOLOGICAL EVALUATION OF A MODIFIED JET TRANSPORT
PASSENGER OXYGEN MASK

» Introduction

This report describes altitude chamber experi-
1ents conducted with human subjects using new
ierra Engineering Series 289-601 disposable
assenger oxygen masks. ‘These masks, applic-
ale for emergency use to 40,000-foot altitudes,
iffer in configuration from the previous Sierra
ask (although both are designed to meet. re-
uirements of NAS 1179 and FAA TSO C-64)
. that the inner face flap or seal has been elim-
ated and the cylindrical shape reduced to a
odified cone.
The unique characteristics of continuous-flow
xygen masks, in terms of human respiration,
‘e frequently not well understood. Although
3s costly than crew masks and deceptively
mple in appearance, continuous-flow passenger
asks have physiological performance character-
tics that are relatively complex.
Continuous-flow, phase-dilution type masks,
signed to the NAS 1179 and FAA TSO C-64
quirements, employ a unique design in which
@ reservoir is interposed between the delivery
be and the mask. The reservoir is separated
om the mask by a sensitive check valve. The
ntinuous flow of oxygen fills the reservoir bag
wing the respiratory pause and exhalation.
ie flow also continues at the same rate during
spiration. The mask-wearer receives 100%
ygen from the reservoir during an entire in-
iration unless the bag is emptied; if this occurs,
spring-loaded valve in the mask opens, and
abient air is introduced to provide sufficient
lume to meet the remainder of the inspiration.
te flow of 100% oxygen is provided at the
ost advantageous point in the respiratory cycle,
the beginning of inspiration. For example,
a human subject’s tidal volume is 650 cc, and
3 reservoir contains only 500 cc at the begin-
ig of inspiration, the 500 ce of 100% oxygen
ll be inspired first and delivered to the active
xas of the lungs. The ambient air valve will

then open and deliver 150 cc of ambient air,
which will enter the mouth, trachea, and other
“dead” or inactive spaces of the respiratory
system. Upon expiration, this dead-space air is
the first to exit through the exhalation valve.
This process is repeated with each respiratory
cycle. In normal practice, the reservoir bags
are capable of containing a maximum of 1,100 ec
which provides for increased tidal and minute
volumes.

In summary, continuous-flow, phase dilution
masks offer the following advantages:

1. Oxygen economy is afforded by use of a
reservoir bag that fills and retains the oxygen
flow during both the respiratory pause and ex-
halation.

2, At lower altitudes, reduced oxygen flow
rates may be employed and the air-oxygen dilu-
tion controlled in a manner more reliable than
other methods employed in constant-flow oxygen
masks.

3. Oxygen concentrations approaching 100%,
required at 35,000 to 40,000 feet, may be obtained
with moderate and reasonable flow rates.

One basic disadvantage of all continuous-flow
oxygen systems is their inability to adjust auto-
matically to the respiratory changes associated
with changes in emotional and physical activity
of the wearer. A healthy young male breathing
air at rest normally exhibits a (volume/breath)
tidal volume of about 550 ce and a minute volume
(volume/minute) of 7,700 cc. Emotional and/or
physical activity may cause these values to in-
crease greatly. Concern with this problem is
reflected in the Federal Aviation Regulations
Part 25 (formerly Part 4B), 25.1443, which re-
quires maintenance of a mean tracheal oxygen
partial pressure of 83.8 mm Hg at a tidal volume
of 1,100 ce, and a 30-liter BTPS (body tempera-
ture pressure saturated) minute volume for alti-
tudes of 18,500 to 40,000 feet.





REFERENCES

. Federal Aviation Regulations, Part 25. Airworthi-
ness Standards, Transport Category Airplanes.

. Evaluation of Prototype Passenger Oxygen Mask
Assemblies, Boeing Airplane Company Report D6-
1954, Transport Division, Renton, Washington, Feb.
9, 1959.

- Qualification Test Report, Passenger Oxygen Mask,
QTR-59-6. Aro Equipment Company of California,
Los Angeles, Calif., Jun. 24, 1959.

National Aerospace Standard, 1179, Revised. Aero-
space Industries Association of America, Washing-
ton, D.C., Mar. 31, 1961.

Federal Aviation Agency: Technical Standard Order
C64, Ang. 28, 1961.

Oxygen Equipment for Aircraft, Aerospace Infor-
mation Report 825. Society of Automotive Engi-
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A Design Analysis of a Jet Transport Passenger-
Oxygen System. Douglas Report SM-42564, Missile
and Space Systems Division, Douglas Aircraft Com-
pany, Santa Monica, California, March 1963.

Luft, U. C.: Evaluation of the K-S Disposable
Oxygen Mask. Special Project. USAF School of
Aviation Medicine, January 1951.

1

9.

10.

i.

138.

14,

. Donaldson, R. T.:

McFadden, E. B.: Evaluation of the Physiological
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April 1966.

NASA Life Sciences Data Book, First Edition, June
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Bryan, C. A, and Leach, W. G.: Physiological Ef-
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Aircraft. Aerospace Medicine 31(4) :267-275, 1960.
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McFadden, FE. B., Harrison, H. F., and Simpson,
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McFadden, E. B., Harrison, H. F., and Simpson,
J. M.: Physiological Evaluation of a Cessna Mask
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22560