Taste 4. Oxygen flow furnished by the Scott automatic constant flow regulator No.
25620-3 as measured at Normal Temperature Pressure Dry (NTPD) 22°C, 760 + 0.5 mm
He, using the orifice supplied with the new prototype version of the Scott Sky Mask. ‘This
mask incorporates a porous dilution valve. Automatic flow by increased pressure was
activated by exposing the regulator to the indicated altitudes and measured as shown in
Figure Seven. One outlet was used and the supply pressure maintained at 335 psi.

Barometric Line Flow Calculated
Altitude (Feet) Pressure Pressure © L/Min NTPD Flow L/Min BTPS.
mm. Hg. p. si.
0 760 40 0.00
8,000 565 42 Less than 1.00
18, 000 380 58 2.05 4.93
25,000 282 7 3.02 10.28
30, 000 226 74 3.63 16, 23
34,000 188 78 3.95 22, 44

Same orifice and conditions as above, but with seven additional Scott Sky Masks plugged
into the system.

0 760 41 0.00
8,000 565 42 Less than 1.00
18,000 380 58 1.98 4.77
25,000 282 70 2,92 9.94
30, 000 226 74 3.46 15.47
34,000 188 78 3.82 21.70

Taste 5. Oxygen flow furnished by the Scott automatic constant flow regulator No.
25620-3 as measured at Normal Temperature Pressure Dry (NTPD) 22°, 760 + 0.5 mm Hg,
using the orifice supplied with the prototype Scott mask. This mask incorporates a mask-
mounted microphone and a phase dilution valve. Automatic flow by increased pressure was
activated by exposing the regulator to the indicated altitude and measured as shown in
Figure Seven. One outlet used and the supply pressure maintained at 335 psi.

Barometric Line Flow Calculated
Altitude (Feet) Pressure Pressure L[Min NTPD Flow L/Min BTPS
mm. Hg, p. 8.4.
0 760 41
8,000 565 44 Less than 1.00

18, 000 380 58 2.15 5.17

25,000 282 70 3.09 10,51

30, 000 226 1 3.67 16.41

34,000 188 79 4.05 23.01

Same orifice and conditions as above, but with seven additional Scott Sky Masks plugged
into the system.

0 760 40
8,000 565 43 Less than 1.00
18, 000 380 58 2.07 4.98
25,000 282 71 3.00 10.21
30, 000 226 75 3.54 15.83
34,000 188 79 3.92 22.27

i



analyzed composition of end expiratory gas
withdrawn from a sampler inserted into one
nostril (Figure 4).

Fiaure 4.—Two sizes of end expiratory nasal samplers
and integrating reservoir.

In the evaluation of oxygen mask efficiency,
one of the most important factors is the partial
pressure of gases in the inspired gas. A re-
breathing mask defies direct measurement of
these parameters, due to the rapidly varying
non-homogeneous gas mixtures introduced from
instant to instant in the facepiece of the mask.
The per cent of gases in the facepiece of the
mask is averaged by an integrating reservoir
and indicates a trend, but this average is in-
fluenced 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 technique is based on
the assumption that the end expiratory gases
from the lungs have become mixed and represent
a homogeneous mixture.

‘As an inert gas, nitrogen does not participate
in metabolic exchange. If the absorption of O2
and the production of CO. were exactly the
same, the amount of nitrogen inspired would

equal the amount expired; ie., nitrogen mole-
cules inspired = nitrogen molecules expired.
The metabolic respiratory quotient (R.Q.) would
_ COz produced
~ “Og consumed
and is not normally equal to one, or unity. Un-
der these conditions there may be a relative dif-
ference in the per cent of inert nitrogen inspired
and expired. (The metabolic R.Q. depends upon
the predominance of carbohydrates (1.0), pro-
tein (0.82) or fat (0.71) being metabolized).
The normal value of a mixed diet approximates
0.83, The respiratory R.Q. may vary temporar-
ily from the metabolic R.Q. due to unsteady
states such as hyperventilation. The increased
lung ventilation produces a blow-off of CO:
from the blood and an apparent but misleading
increase in CO, production with a resultant R.Q.
greater than 1.0. Conversely, hypoventilation
and retention of CO, indicate an apparent but
misleading decrease in CO, production which
results in an R.Q. less than 0.7.

One must keep in mind that the unequal ex-
change 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 oxygen were consumed
and 0.25 liters of CO2 produced (R.Q. = 0.88),
the resultant difference of 0.05 liters on the seven
or eight liters passing through the lungs during
the same period of time is relatively small. This
produces an error of only a few per cent, well
within the experimental error of the determina-
tions of end expiratory nitrogen.

All nitrogen diluting the inspired gas origi-
nates from ambient air with the exception of
nitrogen derived from the tissues which, after
six to eight minutes of breathing oxygen under
a steady state condition, has been shown to con-
stitute less than one per cent of the lung volume.

equal one. The metabolic R.Q.

Using calculations suggested by Luft’, the ad-

mixture 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

Using these formulas, the percentage of dilu-
tion, supply oxygen, oxygen from the ambient



310
300
290
280
270
260
250
240
230
220 F
210 F
200 F
190 F
180
170 F

fo)

160 F
150 F
140 F
130 F
120 F-
HOF

1 1 j
100 18 25 30 34

ALTITUDE THOUSANDS OF FEET

Fieure 10.—Comparison of calculated resting tracheal
oxygen partial pressures. Summary of data from
Tables 1, 2 and 3.

TRACHEAL OXYGEN PARTIAL PRESSURE

% DILUTION VALVE MASK
@ POROUS DILUTION PORT MASK
© OPEN DILUTION PORT MASK

oxygen partial pressures than the similar mask
equipped with open dilution ports. Had oxygen
flows been lower it is anticipated that this dif-
ference would be exaggerated. In addition, if
the tracheal oxygen partial pressure is reduced
to a point approximating 90 to 100 mm Hg,
hypoxic drive of respiration may ensue. In this
case, a vicious cycle may develop when using
constant flow diluter masks in that the mask

300 -
290 Ff
280 F
270

% DILUTION VALVE MASK
@ POROUS DILUTION PORT MASK
O OPEN DILUTION PORT MASK ~
260 +
250 +
240 +
230
220
210
200
190 £
180 + ©
170 + i
160 +
150 +
140
130 +
120 F if
lo F y
J

100 : ;
18 25 30 34

ALTITUDE THOUSANOS OF FEET.

Figure 11—Comparison of calculated tracheal oxygen
partical pressures during exercise. Broken lines and
arrows at 30,000 and 34,000 feet indicate magnitude
of depression of tracheal oxygen partial pressure
induced by high inspiratory flows characteristic of
speech (reading). Summary of data from Tables
1, 2 and 3.

TRACHEAL OXYGEN PARTIAL PRESSURE

of——0

wearer may reflexly hyperventilate. The in-
creased ventilation results in more ambient air
being drawn into the mask, diluting the oxygen,
which in turn increases hypoxia and hyperventi-
lation, continuing reduction of mask efficiency
and resulting in an increased deterioration of
the physiological condition of the mask wearer.



air, and total oxygen may be derived according

to the following calculations :

Per Cent Dilution Se ee
Oxygen from supply = 100 Per cent of dilution
Oxygen from ambient = Per cent dilution +
oxygen from ambient
Total oxygen = oxygen from supply + oxygen
from ambient

Calculated inspired oxygen partial pressure =
(Pz - 47) x Per cent total oxygen
Where: Py = Total pressure in mm Hg at am-

bient altitude,
| 47 = Pressure, in mm Hg, of saturated
| water vapor at body temperature.
| A Waters ear oximeter was affixed to the anti-
| helix of the ear of each subject in order to obtain
blood oxygen saturation under all conditions. A

Statham pressure transducer was connected to
the system in order to record the line pressure
response of the regulator to altitude. Closed
circuit television was utilized in order to monitor
each subject’s condition. Motion picture pho-
tography was also used to record the reservoir
bag condition and volume. Instrumentation of
the subjects is shown in Figure 5.

A bicycle ergometer was modified so that it
could be operated by each subject while seated
in an aircraft type seat. After the subject was
instrumented and ground level baselines recorded,
the chamber pressure was decreased to equivalents
of 10,000 and 14,000 feet for recording of addi-
tional air breathing baselines. Chamber pres-
sure was then increased to an equivalent of 8,000
feet in order to determine the subject’s ability
to equalize middle ear pressure. After the sub-
ject had donned the test mask, the chamber

chamaen
WALL
OXIMETER AMPLIFIER
AND MONITOR:
WITROGEN | | NITROGEN U
SENSOR SENSOR
OXYGEN A
\ a SUPPLY my ry
FINGER ‘
| THGHT
| OFF
|
\
F
LINE PRESSURE PLUG IN ORIFICE Flow r
RECORDER INOICATOR Fy}
ELECTROCARDIOGRAPH
IMPEDANCE H
PHEUMOGRAPH
AMPLIFIER .
PRE AMPLI NASAL SAMPLER =@ INTEGRATOR © EAR OXIMETER
ELECTROCARDIOGRAPH LEADS © IMPEDANCE PNEUMOGRAPH LEADS
STATHAM PRESSURE TRANSDUCER @ CONSTANT FLOW REGULATOR

Ficure 5.—Instrumentation of subjects and diagram of oxygen system.


air, and total oxygen may be derived according
to the following calculations :

Per Cent Dilution = Serre ee

Oxygen from supply = 100 Per cent of dilution

Oxygen from ambient = Per cent dilution +

oxygen from ambient

Total oxygen = oxygen from supply + oxygen

from ambient
Calculated inspired oxygen partial pressure =
(Ps - 47) x Per cent total oxygen

Where: Ps = Total pressure in mm Hg at am-
bient altitude.
47 = Pressure, in mm Hg, of saturated

water vapor at body temperature.

A Waters ear oximeter was affixed to the anti-
helix of the ear of each subject in order to obtain
blood oxygen saturation under all conditions. A

CHAMBER
waLt

OXIMETER AMPLIFIER

Statham pressure transducer was connected to
the system in order to record the line pressure
response of the regulator to altitude. Closed
circuit television was utilized in order to monitor
each subject’s condition. Motion picture pho-
tography was also used to record the reservoir
bag condition and volume. Instrumentation of
the subjects is shown in Figure 5.

A bicycle ergometer was modified so that it
could be operated by each subject while seated
in an aircraft type seat. After the subject was
instrumented and ground level baselines recorded,
the chamber pressure was decreased to equivalents
of 10,000 and 14,000 feet for recording of addi-
tional air breathing baselines. Chamber pres-
sure was then increased to an equivalent of 8,000
feet in order to determine the subject’s ability
to equalize middle ear pressure. After the sub-
ject had donned the test mask, the chamber

AND MONITOR

wrTnooee J

OD

see, |)
12 SUPPLY my

LINE PRESSURE

PLUG IN OnIF
RECORDER we

Oe

TQ
Gh
tA

Va

ELECTROCARDIOGRAPH

IMPEDANCE
PNEUMOGRAPH

PRE AMPLIFIER

WASAL SAMPLER
ELECTROCARDIOGRAPH LEADS © IMPEDANCE
‘STATHAM PRESSURE TRANSDUCER

@ iwrecnator © CAR oximeren —
PHEUMOGRAPH LEADS
@ CONSTANT FLOW REGULATOR

Fieure 5,—Instrumentation of subjects and diagram of oxygen system.

4


@-Orifice supplied with new prototype
2 mask incorporating a porous dilution
a valve. One outlet of system in use.
5 A 45h Scott automatic constant flow oxygen
o regulator No. 25620-3. Supply
w & pressure to regulator 335 p.s.i.
N
2 40F .
Sf
oO
Ras fa
OE ©
& q 3.57 °
ES
72
L ry
BE sO be
Se
ho
Ze 25F
we
S
x
i} 2.0F 8
O- Same orifice with seven additional Scott
Sky masks added to the system.
LS 1 4 4

15 20 25 30 35
ALTITUDE THOUSANDS OF FEET

Ficure 8—Oxygen flow as determined by regulator and
orifice as supplied with mask described above. Plot
of data from Table IV.

@-Orifice supplied with new prototype
mask incorporating a solid dilution
a valve, mask mounted microphone and
~& A. 4.55 Duo-Seal valve. Scott automatic constant
BS flow oxygen regulator No. 25620-3.
° Supply pressure to regulator 335 p.s.i.
a One outlet of system in use. °
25 797 Tf,
= £ é ve
= .
9 — 3.57 °
a 8
EO
ae
3 e,
o 3.0F 2
= =
Se
ae 2s
gs ~
oN
Qe
3S 2.0F
©-Same orifice with seven additional
Scott Sky masks added to the system.
15 L 1 1 1

15 20 25 30 35
ALTITUDE THOUSANDS OF FEET

Fraure 9.—Oxygen flow as determined by regulator and
orifice as supplied with mask described above. Plot
of data from Table V.

Ill. Results.

Oxygen flow as provided by the regulator was
sufficient to maintain the subjects’ indicated
blood oxygen saturations well above their 10,000
and 14,000 feet baselines and equalled or ex-
ceeded their ground level (1,273 feet) baselines
(Tables 1, 2 and 3). It should be emphasized
that the masks were carefully fitted to the sub-
jects to provide a good seal to the face. Addi-
tionally, all subjects were young, healthy males
24-88 years of age with previous high altitude
experience.

From the standpoint of relative efficiency,
calculated inspired oxygen partial pressures in-
dicate that the phase dilution masks which in-
corporated either a porous dilution port or a
dilution valve were comparable (Figures 10 and
11). The open dilution port mask produced
lower tracheal oxygen partial pressures at all
altitudes during rest and exercise. The effect
of one minute of reading aloud was evaluated
at 30,000 and 34,000 feet with this mask. This
activity, due to high peak inspiratory flow rates
and mask displacement, reduced the tracheal
partial pressure to a greater extent than did
exercise (Figure 11). However, since reading
was limited to one minute, the reduced tracheal
partial pressures did not appear to produce a
significant effect upon the blood oxygen satura-
tion.

The flows as provided by orifices furnished
with the porous dilution port mask and solid
dilution valve may be compared in Tables 4 and
5. Although the orifice furnished with the
prototype mask incorporating a solid flutter
type dilution valve provided slightly higher flow
rates, this appears to be a function of manufac-
turing tolerance.

IV. Discussion.

The Scott Oxymatic automatic constant flow
regulator when equipped with the proper orifices
and efficient masks is designed automatically to
provide sea level equivalents of oxygen flow to
an altitude of 30,000 feet. Physiological evalua-
tion of subjects at altitude indicated that the
system, when utilized with new prototype re-
breathing masks, maintained the subject’s blood
oxygen saturation and inspired tracheal oxygen
partial pressure equal to or in excess of the
ground level equivalent. Masks of this type
provided higher and more consistent tracheal


AM 67-9

PERFORMANCE CHARACTERISTICS OF CONSTANT-FLOW
PHASE DILUTION OXYGEN MASK DESIGNS FOR
GENERAL AVIATION

Ernest B. McFadden, M.S.
Hiley F. Harrison
James M. Simpson

Approved by Released by

S ir A PYS8, 4
P. V. Srecxr, “

J. Rosert Diniz, M.D.
Cmumr, Crvm Azromepicat InstiruTe Fepera Arr Surcron

May 1967

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



Taxus 1. Physiological response of subjects wearing the new prototype version of the Scott Sky Mask incorporating a
porous dilution valve. Flight profile as shown in Figure 1. Oxygen flow as determined by single metering orifice is
shown in Table 4.

Oxi- Line % Oxygen % O2 Total % Oz Baro- Insp. O2

Resp. Heart meter Pres- % End %Dilu. From From Supply-+ metric Partial

Subject Activity Altitude © Rate Rate % Sat. sure Exp. tion Supply Am- %Am- Pressure Pressure
ft. psi, Na bient dient (P —47) (Py —47)x

mm Hg Total Oz

JS. Resting Ground 15 69 97.0

Resting 10,000 20 81 89.3
%Ne Resting 14,000 20 76 85.5
MEAN Exercise 14,000 26 101 84.0

15 Resting «18,000 «12S 74-«497.0 538.0 10.0 90.0 2.0 92,0838 806
38 Exercise 18,000 :13-« 86.-««97.5 «5338.0 48.0 «52.0 10.0 62.0 388206,
15 Resting «25,000.10. 72:s«96.5 63380 4.09608 97.0 285228
15 Exercise 25,000 15 «87 «98.0 636.0 80 92.016 94.0 28521
10 Resting «30,000 Ss «9s 79 «97.6 «69 4.05.0 9510.0 96.0797
10 Exercise 30,000 16S 8898.0 70 «8.0 «10,0 90.0 2.0 92,0179 165
1 Resting 34,000 «12S 77-s«97.5 78-99. SSK
2 Exercise 34,000 15 «90 «98.0 «730.569.4940
P.F. Resting Ground 18 55 96.0
Resting 10,000 27° «5989.8
%N2 ‘Resting 14,000 22 6487.6
MEAN Exertise 14,000 35 93 86.0
20 Resting 18,000 16 «5396.5 «50 «15,0 19.0 81.0 = 4,085.0 388283
32 Exercise 18,000 28 71 97.0 50 26.0 33.0 67.0 6.9 74.0 333 246
8 Resting 25,000 16 55 97.0 60 4.0 5.0 95.0 1.0 96.0 235 226
13 Exercise 25,000 27° -««73-«97.060«10,0 13.0 87.0 2.6 = 90.0285 212
1 Resting 30,000 2256 «98.0 65S GSH...
8 Exercise 30,000 25 «72 :«98.0 66 «= 4.05.0 95.01.0959 179172
3 Resting 34,000 «16S 60 «99,0 -72,)S«1.0s1.0 99.0.3 99,0440
3.5 Exercise 34,000 28 76 99.0 72 2.0 3.0 97.0 0.5 980 141 138



Hypoxic hyperventilation does not produce
this same effect when air is breathed at, for ex-
ample, 14,000 feet, since the inspired partial
pressure remains constant. Similarly, at higher
altitudes when demand oxygen equipment is used,
the ratio of oxygen to air is accomplished by the
demand regulator which is so designed and pro-
grammed that this ratio remains constant at a
specific altitude regardless of the ventilation and
respiratory activity of the mask wearer. How-
ever, with constant flow systems and masks, dilu-
tion ratios at a specific flow rate are largely
determined by introduction of ambient air into
the mask. Mask design, phase of the respiratory
cycle in which dilution occurs, inspiratory flow
rates and volume are the determiners of the
oxygen/air ratios at a specific oxygen flow.

Although it was not measured, CO2 accumula-
tion in the rebreather bag did not appear to
present a problem with the prototype masks.
In previous mask evaluations it was found that
the use of rapid response infra-red CO, analyzers
which require relatively high sample flow rates
compromised the determinations of end expira-
tory gases. Since the minimum required sample
flow of 250 cc per minute represented a signifi-
cant portion of the inspired gas, it could not be
discarded but was returned by a closed circuit
to the rebreather bag. However, as the sample
was returned to the rebreather bag continuously
and not in phase with the respiratory activity of
the subject, measurement of other expiratory
gases was rendered erratic and erroneous.

The respiratory center is very sensitive to
CO, and it is anticipated that had significant
quantities of CO, accumulated in the rebreather
bag, the subject’s respiratory rate would have
been increased out of proportion to that expected
for the degree of activity in which the subject

was engaged. These data do not indicate this
response.

It must be realized that these evaluations were
carried out at altitude on young, healthy male
subjects under favorable conditions with the
masks correctly donned and providing a good fit
to the face. Under actual conditions of use, care
and caution may not be extended to this degree.

V. Summary and Conclusions.

1. Oxygen flow as provided by the Scott Oxy-
matic automatic constant flow regulator, when
used in conjunction with either of the prototype
phase dilution—rebreather test masks and proper
orifices, was sufficient to maintain the subjects’
indicated blood oxygen saturations equal to or
in excess of their ground level (1,278 feet) base-
lines.

2. With the same oxygen flow rates the proto-
type porous and dilution valve masks provided
higher tracheal oxygen partial pressures than
the open port masks at all altitudes tested during
rest and exercise.

3. The slight reduction of flow rates as pro-
vided by the Scott Oxymatic regulator when
eight orifices were plugged into the system as
opposed to one orifice is not considered to com-
promise significantly the performance of the
system.

4, Heart and respiratory rates of all subjects
indicate normal response, with the maximum
generally occurring during exercise and hypoxia
induced during establishment of air breathing
baselines at 14,000 feet.

5. At the same flow rates a greater amount
of oxygen was derived from the supply and less
lost by the prototype phase-dilution rebreather
masks as compared to the open port type mask.


pressure was decreased to equivalents of 14,000,
18,000, 25,000, 30,000 and 34,000 feet, leveling off
at each altitude with the subject engaged in
three-minute intervals of rest and light exercise
at each altitude (Figure 6).

The bicycle ergometer was operated by each
subject at 45 rpm and a workload'setting of 45

&

DESCEND FOR
EAR CHECK
‘AND DON MASK

oe
a

8

25

AIR
BREATHING
BASELINES

R= RESTING
E + EXERCISE

ALTITUDE / THOUSANDS OF FEET
nr
3

A ee
05 10 15 20 25 30 35 40 45 SO 55 60 65 75
ELAPSED TIME IN MINUTES

Ficure 6.—Altitude chamber flight profile.

OXYGEN SUPPLY
CONSTANT FLOW

REGULATOR SCOTT]
No, 25620-3

ALTITUDE CHAMBER WALL

On
QD has
ort
SCOTT MASK
OXYGEN HOSE ASSEMBLY
OUTLETS

SCOTT MASK
INDICATOR NO, 8540

D
[_[iie3s a

Crwe IN
ORIFICE

a)

watts, approximately equivalent to walking at
a rate of 3.0-3.4 miles per hour on level terrain.

Oxygen flow provided to the mask is a func-
tion of the altitude response of the regulator
which produces an increase in line pressure to
fixed calibrated plug-in orifices incorporated in
the mask hose. As altitude is increased, pres-
sure and resultant flow to the mask are increased,

Oxygen flow, as provided by the regulator
and orifices furnished with the mask, was de-
termined by separately exposing the regulator
to the same altitudes as the human subjects and
recording the flow under standard conditions
outside the chamber as shown in Figure 7. The
capacity of the regulator to maintain pressure
and resultant flow with a single as well as eight
orifices connected to the system, was also de-
determined (Figures 8 and 9). Representative
oxygen flow rates during the human subject tests
with a single outlet in use are shown in the first

portions of Tables 4 and 5.

E PRESSURE
ADJUSTING
E CLAMP

E BROOKS
ROTAMETER
E 0-10 L/min,

TYPE 6-II1
viencuny)

SERIAL
10660-1385/i
MANOMETER

a aoe

Figure 7—Diagram of test method for determining flow characteristics of the automatic constant flow regulator

and orifices.

5.

‘Regulator and outlets installed inside chamber and exposed to altitude.



purposes, one test was conducted using a currently
manufactured Scott Sky Mask incorporating
rebreathing and open dilution ports (Figure 1).

One of the prototype rebreathing masks was
similar in design to the Scott Sky Mask, but
instead of open dilution ports incorporated a
foam porous restrictive dilution port (Figure 2).
The other prototype incorporated a mask-
mounted microphone and a non-porous flapper
type valve in lieu of the open dilution ports
(Figure 3). A Scott automatic constant flow
regulator Model Number 25620-3 and eight
outlets were installed in the altitude chamber
similar to an aircraft installation. Electrocar-
diograph and impedance pneumograph electrodes
were affixed to the subjects in order to obtain
heart and respiratory rates. Mask and end ex-
piratory nitrogen were monitored continuously
by two nitralyzers connected to the mask through
microcatheter tubing (PE 60) of .03 inches in-
ternal diameter. One of the nitralyzers was
connected to an integrating reservoir mounted
on the mask. The other nitralyzer continuously

Freure 1—Subject wearing the open dilution port Scott
Sky Mask engaged in light exercise on the bicycle
ergometer at altitude.

Ficure 2.—Subject wearing a Scott prototype mask in-
corporating a foam porous restrictive dilution port.

Ficure 3.—Subject wearing a Scott prototype mask in-

corporating a nonporous flapper type valve. Mask
is also equipped with maskmounted microphone.


REFERENCES

I. Bert, P. Barometric Pressure, Researches in Eaperi-
mental Physiology (translated from the French by
M. A. Hitchcock and F. A. Hitchcock). College Book
Co., Columbus, Ohio, 1943.

Drayton, F. A. and Cartson, L. D, Evaluation of
Prototype Passenger Orygen Mask Assemblies, Report
No. D6-1954, Boeing Airplane Co., Transport Div.,
Feb. 9, 1959,

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

2.

3.

12

4,

. BALKE,

Koester, N, BE. and Enrmann, E, Emergency Oxygen
Mask Development and Tests. Scott Engineering
Report No, 554, Nov. 30, 1956,

. National Aerospace Standard, NAS-1179, Aerospace

Industries Assn. of Amer.
B. Continuous Determination of Nitrogen
Concentrations During the Respiratory Cycle. Pro-
Ject Number 21-1201-0014, Report No. 5, USAF
School of Aviation Medicine, June 1954,

Lurr, U. ©. Evaluation of the K-S Disposable Oxy-
gen Mask. Special Project, USAF School of Aviation
Medicine, Jan. 1951.


PERFORMANCE CHARACTERISTICS OF CONSTANT-FLOW
PHASE DILUTION OXYGEN MASK DESIGNS FOR GENERAL AVIATION

I. Introduction.

Recent technological advances in general avia-
tion have resulted in the development of aircraft
with increased altitude capability and service
ceilings. On January 11, 1966, a stock model
single-engine Cessna Turbo-System Centurion
set a new world altitude record of 39,334 feet for
light aircraft.

Oxygen in aviation was first used by French
aeronauts and scientists in the famous flight of
the Zenith, a balloon ascension which on April
15, 1875, attained an altitude in excess of 8600
meters (28,000 feet). Oxygen was breathed
from goatskin bags through a scented wash bot-
tle and a small rubber tube held in the mouth.
Unfortunately, in attempting to conserve their
supply of oxygen, these high altitude pioneers
became severely hypoxic and lost consciousness.
Of the three members aboard the Zenith flight,
only one survived. Up until the development of
the constant flow BLB mask just prior to World
War II, the mouth-held tube or pipestem was
still the most common method of administering
oxygen in aviation, Not until late in World
War II and thereafter were the demand and
pressure demand oxygen systems developed.

Constant-flow rebreather type oxygen masks
similar in concept to the BLB are most fre-
quently used in general aviation, due to their
relatively low cost and oxygen economy afforded
at lower altitudes. One basic disadvantage of
constant flow oxygen masks is their inherent
inability automatically to adjust to the require-
ments of the user as influenced by his emotional
or physical activity.

Dilution of oxygen in constant flow masks is
generally afforded by orifices or dilution ports
of a predetermined size which allow a varying
amount of air to enter the mask, depending upon
the oxygen flowing to the mask and the respira-
tory activity of the individual wearing the
mask. Portions of the exhaled gas, higher in

oxygen concentration than air, are returned to
the rebreather reservoir bag for re-use. Other
portions are vented out through the dilution
ports, maintaining carbon dioxide at an accept-
able level. At higher altitudes, it becomes in-
creasingly difficult to control and assure high
concentrations of oxygen with these types of
constant flow or economizer masks unless the
mask is flooded with’ oxygen at uneconomical
flow rates. With the advent in 1955 of require-
ments for short duration emergency protection
of commercial jet passengers to altitudes of
40,000 feet following the loss of cabin pressuri-
zation, the continuous flow phase dilution mask
was developed.*+ This oxygen mask, which
conforms to the National Aerospace Standard
NAS 1179, does not employ rebreathing and is
so designed that 100% oxygen is delivered to the
lungs at the beginning of inspiration® This is
most advantageous since toward the end of in-
spiration air is admitted by a valve only after
the oxygen in the reservoir is depleted. Air in-
troduced by the valve may penetrate the mask
and physiological dead space only. This portion
of the tidal volume is the first to be expelled
upon initiation of exhalation, Air under these
circumstances never reaches the alveoli of the
lungs and is therefore physiologically ineffective.

The continuous flow oxygen masks described
in this report and designed primarily for general
aviation are outgrowths of these developments
and incorporate features of rebreathing and
phase dilution masks.

IL Methods.

Two prototypes of new experimental rebreath-
ing—phase dilution masks manufactured by the
Scott Aviation Corporation were evaluated at
altitude on resting and active subjects, These
tests were designed to evaluate the physiological
adequacy and efficiency of the mask as well as
the oxygen system as an entity, For comparative



Qualified requestors may obtain Aviation Medical Reports from Defense Documentation
Center. The general public may purchase from Clearinghouse for Federal Scientific
and Technical Information, U.S. Dept. of Commerce, Springfield, Va. 22151


Tapte 2. Physiological response of subjects wearing a new prototype Scott mask incorporating a mask-mounted
microphone and phase-dilution valve. Flight profile as shown in Figure 1, Oxygen flow as determined by single
metering orifice is shown in Table 5.

% O2Total % O: Baro- Insp. Oz

Oxi- Line % End % Dilu- % Oxygen From Supply metric Partial

Subject Activity Altitude Resp. Heart meter Pres- Exp. tion From  Am- %Am- Pressure Pressure
ft. Rate Rate % Sat. sure Nz Supply dient bient (P:—47) (Py — 47)x

psi. mm Hg Total 02

C.H. Resting Ground 20 95 96.0

Resting 10,000. 8987.5

Resting 14,000 -_ 100 84.5

Exercising 14,000 17 115 78.0

Resting 18,000 14 85 «97.0 «529.0886 4.833 308
Exercising 18,000 18 92 97.0 52 23.0 29.1 70.9 6.1 77.0 333 256
Resting 25,000 16 86 98.0 60 0.5 0.6 99.4 0.1 995 235 284
Exercising 25,000 19 96 98.5 62 25 3.2 968 0.7 97.5 235 . 229
Resting 30,000 17 87 «99.0 69 0.0 0.0 100.0 0.0 100.0 179 179
Exercising 30,000 23 101 97.0 69 0.5 0.6 99.4 0.1 99.5 179 178

Resting 34,000, ee eee
0.5 Exercising 34,000 22 105 99.0 72 0.2 0.3 998 O12 998 141 141

G.F. Resting Ground 22 88 95.5

Resting 10,000 19 87 92.0
%N2 “Resting «214,000 2292 88.0
Mean Exercising 14,000 26 122 82.0

12.0 Resting 18, 000 20 81 97.5 52 9.0 1.4 88.6 2.4 91.0 333, 303
40.0 Exercising 18,000 27 99 98.2 52 37.0 46.8 53.2 9.8 63.0 333 210
0.0 Resting 25,000 21 87 «97.2 61 0.0 0.0 100.0 0.0 100.0 235 235
33.0 Exercising 25,000 24 107 98.0 61 26.0 33.0 67.0 7.0 74.0 235, 174
1.0 Resting 30,000 19 89 97.2 69 0.5 0.6 99.4 0.1 99.5 179 178
13.0 Exercising 30,000 27 «109 98.0 697.0 8.9 91.1 1.8 92.9 179 166
0.5 Resting 34,000 22 90 96.5 72 0.2 0.2 99.8 0.1 99.9 141 141
1.0 Exercising 34,000 29 106 «97.2 72 0.5 0.6 99.4 0.1 99.5 141 140

Tazz 3. Physiological response of a subject wearing a Scott Sky Mask incorporating open dilution ports. Flight profile
as shown in Figure 1 with the exception that for the first minute of each three minute resting period at 30 and 34,000 feet
the subject was requested to read in order to evaluate the effect of speech upon mask performance. Oxygen flow as
determined by the single metering orifice shown in Table 4.

% Or Total %0: Baro- Insp. Oz

Oxi- Line % End % Oxygen From Supply+ metric Partial

Subject Activity Altitude Resp. Heart meter Pres- Exp. % Dilu- From Am- %Am- Pressure Pressure
ft. Rate Rate % Sat. sure Nx tion Supply dient ~—bient-- (P:47) (Py —47)x

psi. mmHg Total Oz

C.B. Resting Ground 15 74 (95.3

Resting 10,000 17-75 (91.3
%N2 ‘Resting «14,000 16 7889.5
MEAN Exercising 14,000 20 99 83.3

32 Resting 18, 000 16 77 96.0 52 30 38.0 62.0 8.0 70.0 333 233
40 Exercising 18,000 19 92 96.5 53 38 48.1 51.9 10.1 62.0 333, 206
22 Resting 25,000 17 78 96.0 62 18 22.8 17.2 4.8 82.0 235 193
25 Excerising 25,000 21 97 96.5 62 23 29.1 70.9 6.1 77.0 235 181
30 Reading 30,000 21 97 96.5 70 27 34.2 65.8 7.2 73.0 179 131
15 Resting 30, 000 17 87 97.0 70 13 16.4 83.6 3.4 87.0 179 156
18 Exercising 30,000 20 96 «496.2 70 16 20.2 79.8 4.2 84.0 179 150
26 Reading 34,000 19 102 95.5 74 24 30.4 69.6 6.4 76.0 141 107

9 Resting 34,000 18 82 97.2 74 4 5.0 95.0 1.0 96.0 141 135
15 Exercising 34,000 22 94 96.5 74 13 16.5 83.5 3.5 87.0 141 123

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