U.S. patent number 3,794,021 [Application Number 05/195,199] was granted by the patent office on 1974-02-26 for dual mode mixed gas breathing apparatus.
Invention is credited to Christian J. Lambertsen.
United States Patent |
3,794,021 |
Lambertsen |
February 26, 1974 |
DUAL MODE MIXED GAS BREATHING APPARATUS
Abstract
Breathing apparatus, including provisions for carbon dioxide
scrubbing and rebreathing, wherein basic resting oxygen supply is
maintained by constant mass flow of an oxygen-containing gas, and
oxygen in a ventilating gas in excess of the basic requirement is
provided, in each inhalation cycle, by a demand valve actuated by
collapse of a flexible gas storage chamber, the expansion of which
is limited to normal exhalation volume for a predetermined level of
physical exertion and means for dumping the exhalation volume in
excess of that amount and sub-assemblies of such apparatus. By
utilizing, as the demand supplied gas, a gas leaner in oxygen than
that supplied at a constant mass flow rate, the tendency to oxygen
toxicity during periods of exertion is reduced. Preferably, the
system includes a flow-responsive, fail-safe valve to inactivate
the rebreather circuit upon failure of the constant mass flow
supply.
Inventors: |
Lambertsen; Christian J.
(Ardmore, PA) |
Family
ID: |
22720419 |
Appl.
No.: |
05/195,199 |
Filed: |
November 3, 1971 |
Current U.S.
Class: |
128/204.28;
128/205.17 |
Current CPC
Class: |
A62B
7/00 (20130101) |
Current International
Class: |
A62B
7/00 (20060101); A62b 007/04 () |
Field of
Search: |
;128/142.2,142.3,142,140,142.4,147 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,130,272 |
|
Feb 1957 |
|
FR |
|
969,272 |
|
Sep 1964 |
|
GB |
|
Primary Examiner: Rosenbaum; Charles F.
Assistant Examiner: Cohen; Lee S.
Attorney, Agent or Firm: Paul & Paul
Claims
I claim:
1. Dual mode breathing apparatus comprising
a. first and second gas source inlet lines connected to high
pressure sources of a first and a second oxygen-containing
breathing gas, respectively, said first gas having a higher partial
pressure of oxygen than said second gas,
b. a collapsible gas storage chamber with gas storage chamber inlet
and gas outlet lines, said chamber having a first positive means to
permit gas to flow, upon collapse of said chamber, from said second
gas source inlet line to said gas storage chamber outlet line, and
a second positive means to limit the volumetric expansion of said
chamber to no more than one liter,
c. means for delivering said first gas from said first gas source
inlet line at a constant mass flow rate to said collapsible gas
storage chamber and further including a closed breathing chamber
adapted to communicate with the breathing passages of a user of
said apparatus, said breathing chamber also communicating with said
gas outlet line from said collapsible gas storage chamber through
an inhalation valve means and with said gas inlet line to said
collapsible gas storage chamber through an exhalation valve
means.
2. Breathing apparatus, as recited in claim 1, further including
means for removing carbon dioxide from gas flowing in said gas
inlet line of said collapsible storage chamber.
3. Breathing apparatus, as recited in claim 1, further including a
dump valve means for releasing gas from said collapsible chamber to
the environment surrounding said apparatus in response to said
collapsible chamber reaching its fully expanded state and the
pressure in said chamber exceeding that in said environment by some
predetermined increment.
4. Breathing apparatus, as recited in claim 3, and further
including a means, downstream of said dump valve, for removing
carbon dioxide from gas flowing in said gas inlet line of said
collapsible storage chamber.
5. Breathing apparatus, as recited in claim 1, wherein said
breathing chamber comprises a mouthpiece adapted to engage the
mouth area of a user of said apparatus.
6. Breathing apparatus, as recited in claim 1, wherein said
collapsible gas storage chamber comprises a flexible enclosure
housed in a rigid supporting member having openings therein, said
flexible enclosure including a rigid portion adapted, upon collapse
of said enclosure, to engage a valve operator which together with
its associated valve comprises said first positive means recited in
part (b) of claim 1.
7. Breathing apparatus, as recited in claim 1, further including a
sensing means for sensing a failure in said constant mass flow and
for interrupting gas flow from said storage gas chamber inlet to
said breathing chamber in response thereto.
Description
This invention pertains to breathing apparatus, usually used as a
self-contained portable unit, useful to provide breathing gas in a
hostile atmospheric environment, such as, under water, in heavy
smoke, in noxious atmospheres, etc. More specifically, it relates
to a system incorporating rebreather and selective dumping
characteristics and inherently safer due to redundancy and
automatic compensation for decreased oxygen tolerance during
periods of physical exertion.
Various types of breathing apparatus systems, particularly portable
breathing apparatus carried in a backpack by underwater swimmers,
fire fighters, etc., have been developed. Each of these systems has
certain characteristic disadvantages. For example, one such system
supplies gas in response to the demand of the user, based on the
negative pressure in the system produced by inhalation. This type
of system is typically open circuit, i.e., the entire volume of
exhalation gas is simply vented from the system. Therefore a large
volume of breathing gas must be carried in the portable
apparatus.
In other prior art systems, a constant flow of breathing gas is
supplied, and exhalation gas is either partially or fully recycled.
Recycled exhalation gas must, of course, have the carbon dioxide
removed therefrom and this is typically done by contact with
CO.sub.2 absorbent material. It is also known that the last part of
the exhalation gas is that which is highest in CO.sub.2 content,
and selective dumping of this part of the exhalation gas conserves
breathing gas by permitting recycle of exhalation gas substantially
lower in CO.sub.2 content and from which less CO.sub.2 must
therefore be removed.
Constant supply systems necessarily involve a trade-off as to
volume of gas and oxygen content of gas supplied. In order to
reduce the total volume of the portable supply, it is desirable
that a high oxygen concentration in the supply gas be maintained.
However, high oxygen concentration in the gas breathed is
undesirable under certain conditions particularly at high ambient
pressures such as at some depth under water and during periods of
physical exertion at high ambient pressures when the user is
predisposed to oxygen toxicity. Moreover, the constant supply must
necessarily be sufficient to provide for the oxygen requirements of
a user during periods of physical exertion, in which case the
supply is in excess of that needed during periods of rest.
In still other types of breathing apparatus, a closed circuit is
used, i.e., breathing gases are continually recycled, and oxygen is
added to the system only as necessary to maintain some
predetermined oxygen level in the breathing gases. The
disadvantages of this type of system are the inherent difficulties
in sensing and maintaining proper oxygen concentration and the
inconvenience of varying the oxygen content, depending on whether
the user is at rest or in a period of physical exertion. Failure to
take this variable into account also may lead to excessive oxygen
concentration during a period of physicial exertion at high ambient
pressure and predisposition to oxygen toxicity as a result.
It is therefore an object of the present invention to provide a
hybrid breathing system wherein the various disadvantages are
eliminated.
Another object of this invention is to provide a portable breathing
apparatus which is inherently efficient with respect to the volume
of gases used.
Still another object of this invention is to provide a breathing
gas system wherein the oxygen level is automatically
physiologically controlled to compensate for the decreased oxygen
tolerance of a user during periods of physical exertion at
increased ambient pressure.
These and other objects, which will be apparent in the course of
the subsequent description, are met by a breathing apparatus which
includes means for supplying two separate breathing gases, one of
which has a higher oxygen content, or partial pressure, than its
counterpart. That gas having the higher oxygen content is supplied
at a constant mass flow rate through a collapsible gas storage
chamber, the expansion of which is limited to a predetermined
volume generally corresponding to the exhalation volume of a user
at rest or during a period of limited physical exertion. The
collapsible gas storage chamber also includes means, such as a
rigid portion engaging a valve operator, to permit gas to flow, in
response to the collapse of the collapsible storage chamber, from
that gas supply having a lower oxygen content. The gases thus
supplied are then delivered through an outlet line in the
collapsible gas storage chamber, to the user. Typically, the user
would receive the breathing gases thus supplied through a closed
breathing chamber adapted to communicate with the breathing
passages of the user and also communicating, through an inhalation
valve, with the gas supply line. Preferably, this closed breathing
chamber comprises a mouthpiece or mask of conventional design, also
including an exhalation valve through which the mouthpiece or mask
communicates with a recycle line by which exhalation gas is
delivered through a carbon dioxide removing means, such as a
chemical CO.sub.2 scrubber, back to the collapsible gas storage
chamber. After the collapsible gas storage chamber has been fully
expanded by the exhalation gas, any excess exhalation gas is vented
by an overpressure or dumping valve provided for that purpose.
By limiting the volume of the collapsible gas storage chamber to
the volume of a normal inhalation of a resting individual the
hazard of failure of gas flow is limited by the physiological
tendency to take deeper breaths when a gas is partially rebreathed
to the point of lowering the inspired oxygen concentration. Such
deeper inhalation draws new gas from the demand supply system on
emptying the collapsible reservoir then, on exhalation, conserves
the oxygen in the last portion of the inhalation (the "dead-space"
oxygen) by exhaling it into the collapsible storage container and
selectively discharging the gas with lower oxygen concentration
from the last portion of the exhalation. Preferably, a
flow-sensitive valve, which closes in response to a failure of the
constant mass flow gas supply, prevents passage of any exhalation
gas back to the collapsible gas storage chamber in the event of
such failure, thereby converting the system to a straight
demand-supply system and preventing rebreathing of oxygen-depleted
gas.
This invention may be better understood by reference to the
following detailed description, taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a schematic assembly view of a breathing apparatus
subassembly embodying the basic features of the present
invention;
FIG. 2 is a cross-sectional detail view of a fail-safe valve which
may be incorporated in a breathing apparatus of the type taught
herein;
FIG. 3 is a schematic assembly view of a breathing apparatus in
accordance with the present invention, in which a subassembly
slightly different than that shown in FIG. 1 is utilized;
FIG. 4 is a cross-sectional detail view of an overpressure valve
shown in the assembly view of FIG. 3;
FIG. 5 is a series of graphical illustrations of gas flows in a
system of the type shown in FIG. 3.
Referring more specifically to FIG. 1, there is shown a schematic
illustration of a subassembly incorporating the basic features of
the present invention. More specifically, a collapsible gas storage
chamber 2, housed in a perforated rigid enclosure 4 which limits
its volumetric expansion, but exposes it to ambient pressure,
communicates with gas inlet line 6 adapted to receive breathing gas
with a relatively high conventration of oxygen delivered through a
constant mass-flow metering device, all of which is not shown in
FIG. 1. Line 6 delivers breathing gas through orifice 8 to chamber
2. A second gas inlet line, namely, demand flow gas inlet line 10,
is adapted to receive breathing gas of relatively low oxygen
concentration from a source thereof and through a pressure reducer
such that gas is delivered through inlet line 10, at a
predetermined pressure increment above ambient, through orifice 12
and demand valve 14 (shown in a closed position in FIG. 1), to a
lower section 16 of chamber 2. Lower section 16 of chamber 2
communicates with the main part of chamber 2 through fail-safe
valve 17 and is closed at its opposite end by diaphragm 18, which
operatively engages demand valve actuator 20 so that demand valve
14 is opened in response to collapse of diaphragm 18. Diaphragm 18
is also protected from and exposed to ambient pressure by a rigid
perforated housing 22. Collapsible gas storage chamber 2 together
with the lower section thereof 16 also include a gas outlet line 24
adapted to be connected to a breathing chamber or breathing mask or
mouthpiece through an inhalation valve 26, which opens in response
to the negative pressure produced by inhalation. Inhalation valve
26 may be located in the breathing apparatus subassembly shown in
FIG. 1 or alternatively may be located in the breathing chamber,
mask, mouthpiece, etc. Similarly, collapsible gas storage chamber 2
communicates with a gas inlet line 28 adapted to communicate,
through an exhalation valve 30, with the breathing chamber, or
breathing mask, or breathing mouthpiece, which in turn is in
communication with the breathing passages of a user of the
apparatus.
Collapsible gas storage chamber 2 communicates with lower section
thereof 16 through fail-safe valve 17, which is maintained in the
open position by bellows 32 under the pressure of the constant mass
supply gas with which bellows 32 is in communication through
orifice 34. Valve member 36 is seated against separator 38, which
separates the upper part of collapsible gas storage chamber 2 from
the lower part 16 thereof, in response to a drop in the pressure of
the constant mass gas supply. This closes the rebreather circuit in
the event of failure or exhaustion of the constant mass gas supply
converting the system to an open circuit demand system and
preventing rebreathing of oxygen-depleted gas. Valve 14 then
becomes operative to supply gas, directly from the demand
supply.
In the operation of a breathing apparatus incorporating the
subassembly shown in FIG. 1, a constant mass flow of gas with a
relatively high oxygen content, calculated to satisfy, for example,
the basic metabolic needs of a user at rest and under other given
conditions, is introduced through inlet line 6. Breathing gas in
collapsible gas storage chamber 2 is exhausted to the user on
inhalation through inhalation valve 26 and outlet line 24. During
exhalation, the exhalation gas is returned to collapsible gas
storage chamber 2 through inlet line 28 and exhalation valve 30
after passing through a carbon dioxide removal means, not shown. By
use of high mass flow of gas with a small volume for the
collapsible gas storage chamber the requirement for a carbon
dioxide removal means can be eliminated. An overpressure valve 40
may be used to vent excessive pressure in storage chamber 2,
although such an overpressure valve is preferably located, as
described more fully hereinafter, at or near the breathing mask or
breathing chamber upstream of the carbon dioxide removal means.
In the event the breathing gas needs of the user exceed that
provided by the constant mass flow supply line, such as in periods
of physical exertion, the volume of gas in storage chamber 2 and
provided contemporaneously with inhalation by constant mass supply
line 6 will be inadequate. The negative pressure of inhalation then
causes collapse of diaphragm 18 thereby opening demand valve 14
through actuation of demand valve actuator 20 and thus providing
for the delivery of additional breathing gas, as required, to the
breather through inhalation valve 26.
To prevent rebreathing of breathing gases exhausted of their
necessary oxygen content, fail-safe valve 17 closes upon exhaustion
of the constant mass flow gas supply or a drop in pressure thereof.
Obviously, various other types of sensing means, such as pressure
sensors, rotometers, etc. may also be used to sense a failure of
the constant mass flow. Thereafter, the rebreathing circuit is
closed and the apparatus operates as a pure demand system with
valve 37 closing and opening, respectively on exhalation and
inhalation. As in any demand system, the user is warned of
approaching supply exhaustion by difficulty in inhalation due to
pressure drop in the supply. Similarly, if the demand supply fails,
the volume of the collapsible gas storage chamber 2 is too small
for full inhalation in even moderate exertion, providing immediate
warning of failure of the demand supply. The volume of constant
mass flow supply will ordinarily be inadequate to meet a user's
needs for inhalation in periods of physical exertion, thereby also
making inhalation difficult. In either event, therefore, the user
is warned of system failure. If the demand system gas supply fails
and physical exertion is continued the limitation of inhalation
volume is accompanied by a progressive decline in inspired oxygen
concentration from the rebreathed gas in the collapsible gas
storage chamber, due to metabolic consumption of oxygen. At rest
the inspired oxygen concentration will not fall.
Because the additional gas needed for breathing during periods of
physical exertion is provided by the demand supply which is of a
lower oxygen concentration or partial pressure, the danger of
oxygen toxicity caused by breathing of high oxygen content gas
during periods of physical exertion is inherently minimized in the
hybrid breathing system of the present invention.
Turning now to FIG. 2, there is shown in detail an improved form of
fail-safe valve 17, in which constant mass flow gas supply passes
through orifice 34 into bellows 32 and thence, when valve 17 is
open, out of bellows 32 and through separator 38. In this
embodiment of valve 17, valve member 36, valve stem 42, and valve
operator 48 are moved via valve guide 44 into the open position by
the constant mass flow gas stream. Bellows 32 encounters stop 33
preventing its further expansion when valve 17 is open. Failure of
this constant mass flow stream permits relaxation of valve spring
46 and the collapse of bellows 32, in turn causing valve member 36
to seat on separator 38.
In FIG. 3, a somewhat different form of breathing apparatus
subassembly (than that shown in FIG. 1) is shown as is an overall
breathing apparatus in which it is incorporated. Using like numbers
to refer to members previously described, collapsible gas storage
chamber 2, the volumetric expansion of which is limited by
perforated rigid enclosure 4 (through which collapsible gas storage
chamber 2 is exposed to ambient pressure) communicates through
fail-safe valve 17 (of the type shown in FIG. 2) with the
inhalation tube 52 of a breathing mask or mouthpiece 54, in which
is included inhalation valve 26 and exhalation valve 30. Through
exhalation valve 30, breathing mask 54 communicates with exhalation
tube 56 through which exhalation gases are passed to a carbon
dioxide cannister or scrubber 58 (conventionally a housing
containing a chemical absorbent for carbon dioxide) and thence back
through fail-safe valve 17 to collapsible gas storage chamber 2.
Relatively high oxygen concentration breathing gas is supplied
through a constant mass flow metering device, not shown, inlet line
6 and bellows 32 of fail-safe valve 17 to collapsible storage
chamber 2. When gas from line 6 and from the rebreathing circuit is
inadequate, such as in periods of physical exertion, perforated
plate 60 in collapsible gas storage chamber 2 operates demand
actuator 20 to open demand valve 14 and thereby provide additional
breathing gas, of lower oxygen concentration for reasons described
above, from demand gas flow inlet line 10.
On exhaustion of or other failure of the mass flow gas supply and
consequent closure of the fail-safe valve 17, inhalation of gas
released into storage chamber 2 from demand valve 14 occurs via
one-way valve 37, the opening of which is assisted by the negative
pressure in the inhalation tube 52 operating on the downstream side
of the valve 37 which is responsive to a pressure difference across
its face.
Overpressure, exhaust or dump valve or vent 40 in this embodiment
of the invention is located near or in the breathing mask or
mouthpiece 54. As shown in FIG. 4, the exhaust valve here utilized
comprises a rigid perforated enclosure 62 with bellows 64 tending
to hold valve member 66 in its closed position seated against
separator 69. Bellows 64 communicates with pressure-compensating
tube 68 by which valve member 66 is biased into the closed position
with a pressure equal to that in the breathing gas storage chamber
2, which is in turn balanced against ambient pressure by virtue of
its exposure to ambient through perforated enclosure 4.
Thus upon exhalation, the exhalation gas is delivered
preferentially through the CO.sub.2 scrubber to the collapsible gas
storage chamber 2. Preferably the volume of that chamber in its
fully expanded condition is a predetermined volume related to the
expected exhalation volume of the user under some preset condition
such as a user at rest. In that case, the system will effectively
be a total rebreather system. However, when the exhalation volume
exceeds this amount, such as in periods of physical exertion, the
exhalation will produce a pressure build-up such that the pressure
on valve member 66 will exceed by some predetermined increment that
in collapsible gas storage chamber 2 and force valve member 66 to
open, thus venting the remainder of the exhalation gas. Since it is
well known that the last part of an exhalation is substantially
higher in carbon dioxide content, particularly during periods of
physical exertion, than those portions of the exhalation which
precede it, location of dump valve 40 upstream of CO.sub.2 scrubber
58 causes dumping of that gas containing a maximum of CO.sub.2
thereby prolonging the life of the CO.sub.2 scrubber chemical by
reducing the amount of CO.sub.2 which it must remove.
The function of the breathing apparatus of the present invention
may best be illustrated by the graphical analysis of various gas
flows into and from the system and within the system shown in FIG.
5. As the graph titles in FIG. 5 indicate, gas flow is illustrated
for four sets of conditions, namely, with the user at rest in an
ambient pressure of 1 atm., with the user in a period of physical
exertion at an ambient pressure of 1 atm., with the user at rest in
an ambient pressure of 3 atm., and with the user in a period of
physcial exertion in an ambient pressure of 3 atm. The first
horizontal set of curves illustrate tidal volumetric flow to and
from the user. It will be noted that volumetric flow is roughly the
same at rest regardless of whether the user is at an ambient
pressure of 1 atm. or 3 atm., but substantially higher during
periods of physical exertion at the two ambient pressures
illustrated.
The second horizontal set of graphs illustrate that the volumetric
flow rate of the constant mass flow supply is constant regardless
of the physical state of the user, but is substantially reduced
when the ambient, and therefore the system, pressure increases to 3
atm. The cumulative volume flow as the bag is emptied and as it is
filled is shown in the next two horizontal sets of charts, and in
both of these cases it will be noted that the bag is substantially
emptied and substantially filled in phase with inhalation and
exhalation when the user is at rest. During periods of physical
exertion, however, the bag is emptied and filled, respectively,
much faster and the remaining inhalation gas is provided, as shown
in the horizontal set of graphs titled Demand Flow, by the demand
supply which takes over after the bag is completely emptied.
Similarly, the remaining exhalation gas after the first part of the
exhalation has filled the bag, is vented to the ambient environment
as shown in the bottom horizontal set of graphs. Finally, also in
the bottom horizontal set of graphs, entitled Gas Venting
Cumulative Volume, a relatively small quantity of gas is shown to
be vented in each breathing cycle even when the user is at rest.
This corresponds roughly to the volume of diluent gas introduced
into the system along with the constant mass flow supply when that
supply utilizes a breathing gas with an oxygen content of less that
100 percent.
The graphical analyses as shown in FIG. 5 are not drawn to scale
and are based on estimated relative proportions rather than tests
or numerical calculations.
In Table 1 (below) there is shown a summary of various gas flows
and volumes, as well as gas concentrations, for various conditions
of collapsible chamber storage volume, user's physical state (at
rest or in a period of exertion) and for various constant mass flow
rates in a system of the type shown in FIG. 3. It will be noted
that two values of CO.sub.2 concentration are given, the first of
which is the CO.sub.2 content of the exhaled gases at the end of
the inhalation cycle, and the second is the average in the total
exhalation. The values for breathing volumes and concentrations are
all based on physiological tests. The gas flow rates and
concentrations within the system are based on calculations for
these various sets of conditions. Nevertheless, Table 1
illustrates, inter alia, that with a constant mass flow supply of
100 percent oxygen, as may be tolerated by user at rest at one
atmosphere of ambient pressure, the percentage of oxygen in the
breathing gas decreases substantially, to on the order of 20
percent (comparable to ordinary air) under conditions of exercise.
Table 1 also shows various interrelationships between collapsible
chamber volume, constant mass flow rates, oxygen and CO.sub.2
concentrations, and physical state of user which permits the design
and adjustment of a system tailored to the particular needs of any
user.
Other advantages of the breathing apparatus of the present
invention include minimization of the resistance to breathing by
providing peak inspiratory flow from a "fractional breathing bag"
(collapsible chamber less than breathing volume for each cycle) in
parallel with the demand unit. By selection of the appropriate,
small volume for the "fractional breathing bag," the overall
apparatus weight required to accomplish neutral buoyancy for
underwater use is reduced.
Extension of the gas-saver principle, previously patented by the
inventor herein, see U. S. Pat. No. 2,871,854, Lambertsen, retains
the feature of selective dumping of the last part of each
exhalation, with increasing efficiency of CO.sub.2 dumping as the
degree of physical exercise increases.
As mentioned above, employment of dual gases provides for automatic
compensation for the decreased oxygen tolerance of exercise.
While this invention has been described with reference to
particular embodiments thereof, it should be understood that
numerous other embodiments and various modifications of all of
these embodiments may be made within the true spirit and scope of
the present invention. The appended claims are intended to cover
all such embodiments and modifications as would be obvious to one
skilled in the art. ##SPC1##
* * * * *