Note: Descriptions are shown in the official language in which they were submitted.
CA 02198889 2002-11-26
1
GAS ANALYZER CUVETTES
TECHNICAL FIELD OF THE INVENTION
The present invention relates to novel,
improved cuvettes; to methods for manufacturing those
devices and to novel, improved gas analyzers employing
the cuvettes.
DEFINITIONS
Cuvette: a device which is configured to
contain a static or dynamic gas sample and in which the
concentration of a designated gas ixi the sample can be
ascertained.
Sampling Passage: a cavity in a cuvette which
confines a sample composed of one car more gases to a
particular flow path traversed by an optical flow path
between an infrared radiation emitter and an infrared
radiation detector (dynamic sample) or to a particular
location along a flow path of that. character (:static
sample) .
WO 96/07886 PCT/US95/10550
~~.~8889
2
BACKGROUND OF THE INVENTION
U.S. patents Nos. 4,859,858 and 4,859,859
were issued to Knodle et al. on 22 August 1989; and
U . S . patent No . 5 , 15 3 , 4 3 6 was issued to Apperson et
al. on 6 October 1992. These three patents disclose
analyzers for outputting a signal indicative of the
concentration of a designated gas in a sample being
monitored by the apparatus.
The gas analyzers disclosed in the 'R58;
'859, and '436 patents are of the non-dispersive type.
They operate on the premise that the concentration of
a designated gas can be measured by: (1) passing a
beam of infrared radiation through the gas, and (2)
then ascertaining the attenuated level of the energy
in a narrow band absorbable by the designated gas.
This is done with a detector capable of generating a
concentration proportional electrical output signal.
One important application of the invention
at the present time is monitoring the level of carbon
dioxide in the breath of a medical patient. This is
typically done during a surgical procedure as an
indication to the anesthesiologist of the patient's
condition, for example. As the patient's wellbeing,
and even his life, is at stake, it is of paramount
importance that the carbon dioxide concentration be
measured with great accuracy.
In a typical instrument or system employing
non-dispersive infrared radiation to measure gas
concentration, including those disclosed in the '858,
'859, and '436 patents, the infrared radiation is
emitted from a source and focused into a beam by a
mirror. The beam is propagated through a sample of
WO 96107886 PCT/US95/10550
3
the gases being analyzed. Af~terYpassing through the
body of gases, the beam of infrared radiation passes
through a filter. That filter reflects all of the
radiation except for that in a narrow band centered on
a frequency which is absorbed by the gas of concern.
This narrow band of radiation is transmitted to a
detector which produces an electrical output signal
proportional in magnitude to the magnitude of the
infrared radiation impinging upon it. Thus, the
radiation in the band passed by the filter is attenu-
ated to an extent which is proportional to the concen-
tration of the designated gas. The strength of the
signal generated by the detector is consequently
inversely proportional to the concentration of the
designated gas and can be inverted to provide a signal
indicative of that concentration.
In a typical medical application of the gas
analyzers just described, a cuvette is employed to
sample a patient's gas exchange via a nasal cannula or
to connect an endotracheal tube to the plumbing of a
mechanical ventilator. The cuvette confines expired
and inspired gases to a specif is f low path; and it
furnishes an optical path between an infrared radia-
tion emitter and an infrared radiation detector unit,
both components of a transducer which can be detach-
ably coupled to the cuvette.
A typical cuvette is molded from an appro-
priate polymer, and it has a passage defining the flow
path for the gases being monitored. The optical path
traverses the flow path with apertures in the wall of
the cuvette and aligned along and on opposite sides of
the flow passage allowing the beam of infrared radia-
tion to enter the cuvette; traverse the gases in the
WO 96107886 PCT/US95110550
i 'r ~i. : . , . .
~y ~.~ a
4
flow passage; and, after being attenuated, exit from
the cuvette to the filter and radiation detector.
Transmissive sapphire windows in the apertures confine
the gases to the cuvette flow passage and keep out
foreign matter while minimizing the loss of infrared
energy as the beam enters and exits from the cuvette.
Sapphire is a relatively expensive material.
Consequently, cuvettes of the character just described
are invariably cleaned, sterilized, and reused. The
cleaning and sterilization of a cuvette is time
consuming and inconvenient; and the reuse of a cuvette
may be perceived as posing a significant risk, espe-
cially if the cuvette was previously employed in
monitoring a patient suffering from an infectious
disease. Another disadvantage of using sapphire
windows is that adhesive bonding is the only viable
technique for mounting. the windows to the cuvette.
This technique is slow and expensive, and care must be
taken that the windows are accurately positioned.
Efforts have been made to reduce the cost of
cuvettes by replacing the sapphire cuvette windows
with windows fabricated from a variety of polymers.
These efforts have heretofore been unsuccessful.
One, if not the major, problem encountered
in replacing sapphire cuvette windows with windows
fabricated from a polymer is that of establishing and
maintaining a precise optical path length through the
sample being analyzed. This is attributable to such
factors as a lack of dimensional stability in the
3o polymeric material, the inability to eliminate wrin-
kles, and the lack of a system for retaining the
windows at precise locations along the optical path.
WO 96107886 PCT/US95/10550
z1 x$889
One proposal for solving this problem is
made in U.S. patent No. 5,067,492 issued 26 November
1991 to Yelderman et al. The patented approach is to
squeeze the cuvette between two housing segments of
5 the transducer with which it is used in the course of
assembling the cuvette to the transducer. If the same
transducer is employed and if its housing is dimen
sionally stable, this will in theory ensure that the
distance between the two cuvette windows is the same
each time the same cuvette is used.
This solution has major drawbacks. Squeezing
the cuvette is apt to wrinkle or otherwise distort the
perhaps initially not distortion-free plastic windows;
and this may affect the transmittance of the windows
enough to cause a significant error in the concentra-
tion of the gas being monitored. Furthermore, in the
Yelderman et al. design, the windows are spaced
inwardly from the flow passage-associated ends of the
optical path apertures. This leaves cavities communi-
Gating with the flow passage in which unwanted debris
can collect; and these crevices can adversely affect
the flow of gases through the cuvette. Also, the
structure employed to position and retain the plastic
windows in the body of the cuvette is important; and
Yelderman et al. contains only the sketchiest of
suggestions of how this might be accomplished, let
alone a description of a window retaining system that
would minimize wrinkles and other distortions and
accurately hold the windows in place, particularly
considering the squeezing of the cuvette needed to
assemble the cuvette to its adapter. Another problem
with the Yelderman et al. hardware is that of assem
WO 96/07886 PCT/US95/10550
;; t ~, ,
~l9sssy...
6
bling the cuvette to the adapter because of the
interference fit between these two components.
SUMMARY OF THE INVENTION
Now invented and disclosed herein are new
and novel cuvettes which can be manufactured cheap
enough that it is practical to dispose of them after
use with a single patient or if the-cuvette becomes
unusable due to contamination or a dirty window, for
example. At the same time, those novel cuvettes are
free of the defects and drawbacks of previously
proposed cuvettes with sapphire-substitute windows
including the one disclosed in the above-cited Yelder
man et al. patent.
The cuvettes disclosed herein resemble those
heretofore proposed to the extent that they include a
flow passage for the gas(-es) being monitored, aper-
tures to and from the flow passage for transferring
infrared radiation propagated along an optical path
traversing the gases in the flow passage, and radia-
tion transmitting windows in those apertures for
confining the gases) to the flow passage. However,
the cuvettes of the present invention differ from
those heretofore proposed in a number of important
respects.
One is the material from which the windows
are fabricated. The conventional polyethylenes and
polypropylenes heretofore proposed by Yelderman et al.
and others is inherently not very strong in the
thicknesses required for acceptable infrared transmis-
sion. As a result of this lack of strength, such
windows will stretch and move when exposed to the
WO 96!07886 PCT/US95/10550
X198889
~. r
changes in airway pressure inherent in breathing
circuits. The resulting changes in pathlength natu-
rally cause variations in system calibration and
accuracy. Additionally, such windows are very suscep-
tible to damage in the course of normal handling and
installation in the breathing circuit.
Instead of the conventional polymers em-
ployed by Yelderman et al., the windows of the novel
cuvettes disclosed herein are preferably fabricated
from a malleable homopolymer; most preferably a
biaxially oriEnted polypropylene (BOPP), in the
thickness range of 0.001 in to 0.005 in. Polymers of
this character are widely available, strong in thin
gauges, malleable, and relatively transparent to
infrared radiation; and much better control over the
thickness of the film can be obtained.
BOPP offers numerous advantages. The high
strength of BOPP allows the windows to be self-sup-
porting and sufficiently rigid to eliminate the need
to secondarily define the pathlength with the sensor
in order to prevent movement with changes in airway
pressure (In the preferred embodiment described in
Yelderman et al., "portions of the gas analyzer
housing protrude and slightly squeeze the optical
windows of the adapter body so as to accurately locate
the optical windows...so that the membranes of the
optical windows are a predetermined distance from each
other").
BOPP is sufficiently strong to maintain,
without relaxation, the tension imparted during
assembly to produce a flat, distortion-free window.
Also, BOPP windows are more durable and less apt to be
damaged and rendered unusable in normal use. BOPP
WO 96/07886 PCT/US95110550
2198gg9
f i lms are suf f iciently strong to withstand the stress-
es of the mechanical installation and retention. By
the nature of the manufacturing process for BOPP
films, thickness variations are minimized, thus
providing improved reproducibility of the pathlength
and less variability in the optical properties.
Because BOPP's are inexpensive, it is
practical to dispose of cuvettes with windows fabri
cated from these materials after a single use or if
the cuvette should become dirty, contaminated, or
otherwise unusable without cleaning, disinfection, and
the like.
A zero calibration can be performed on the
transducer after the cuvette is assembled to it. This
calibration is important because it allows one to
achieve optimum accuracy by zeroing out spectral
tolerances in the window material. This eliminates
errors which might otherwise be caused by deviations
from nominal tolerances in the lot-to-lot chemical
composition as well as thickness and other physical
specifications of the stock material.
Another advantage of the present invention
is that the polymeric materials from which the windows
are formed are also, by virtue of their biaxial
polymer chain orientation, resistant to wrinkling,
warping, and other forms of accuracy-affecting distor-
tion. Yet they are malleable, which makes the materi-
al easy to form to a shape in which they span and seal
the apertures in the cuvette.
Yet another advantage of employing the
preferred polymeric window materials is that cuvettes
with windows formed from those materials are backwards
compatible. That is, cuvettes with windows fabricated
WO 96!07886 PCT/US95/10550
2~ ~888.~
9
from such materials can be substituted for cuvettes
with sapphire windows without redesigning the trans-
ducers with which the cuvettes are used.
Another significant feature of the present
invention is the mounting of the windows with their
inner faces flush with that surface of the cuvette
bounding the flow passage. This eliminates debris
trapping and flow affecting nooks and crannies such as
those in the Yelderman et al. cuvettes.
Still another important feature of the
present invention is the use of skeletal snap-in
retainers or rings to immobilize the windows at
precise locations in the cuvette bodies. These
retainers can also be employed to collapse the window-
forming material around those components as they are
installed. This provides gastight seals between the
retainers and the body of the cuvette. At the same
type, this novel technique for installing and sealing
the cuvette windows eliminates the need to heat the
windows if heat sealing were employed. This is
important as heat could well ruin the optical flatness
required for accurate carbon dioxide measurement.
Other advantages attributable to the snap
ring system employed to hold the windows in place are:
(1) fast, reliable, inexpensive manufacture
of the adapters is promoted;
(2) adhesives and the attendant require-
ments for careful handling, dispensing, and curing are
eliminated;
(3) heat sealing is not required;
(4) the adapter body can be molded from
high strength polymers which have better dimensional
stability than the conventional polyethylenes and
CA 02198889 2002-11-26
polypropylenes employed by Yelderman et al as the adapter body and
the windows do not have to be fabricated from similar material.
The apertures in the cuvettes are configured to precisely
locate the windows along the gas traversing optical path and the
cuvette is fabricated from a rigid, deformation resistant material.
As a result the length of the optical path can be depended upon to
remain constant within the very close tolerances .required for
accurate measurement without employing the Yelderman et al cuvette
squeezing assembly technique or another equally inconvenient method
of providing an accurate optical path length.
The cuvette apertures are also configured to provide the
just-discussed snap-in assembly of the window retainers to the body
of the cuvette and eliminate the need fax heat sealing or adhesives.
The inner, flow passage-associated ends of the cuvettes are
preferably so dimensioned that a window or retainer can not pass
through the aperture if it is accidentally dislodged. This is a
significant safety feature as it keeps a dislodged retainer or window
from perhaps passing to a mechanical ventilator or other equipment
or, even worse, being pumped through an endotracheal tube into a
patient's lungs.
The invention in one broad aspect provides a gas analyzer
for outputting a signal indicative of the concentration of a
designated gas in a sample which may contain that gas. The gas
analyzer comprises a casing which houses an infrared radiation
emitter, an infrared radiation detector and a cuvette for so
confining the sample that infrared radiation propagated along an
optical path between the infrared radiation emitter and the infrared
radiation detector traverses the gas in the sample. The cuvette
comprises wall means bounding a sampling passage, apertures in the
wall means aligned along the optical path on opposite sides of the
sampling passage and windows in the apertures, the perimeter of each
aperture having an inner segment configured to provide a retainer
stop for locating the window in that aperture relative to a boundary
of the sampling passage and an outer, undercut segment for holding
the retainer against the stop and immobilizing the window in the
CA 02198889 2002-11-26
iaA
selected location relative to the boundary of the sampling passage.
The cuvette divides the casing into firs: and second compartments
located on opposite sides of the cuvette. The infrared radiation
emitter and the infrared radiation detector are located in the first
compartment with the emitter being so oriented as to direct radiation
through the cuvette to the second compartment. The gas analyzer
further comprises mirror means in the second compartment for
redirecting the infrared radiation reaching that compartment back
through the cuvette to the infrared radiation detector.
The objects, advantages and features of the present
invention will be apparent to the reader from the foregoing and the
appended claims and as the ensuing detailed description and
discussion proceeds in conjunction with the accompanying drawings.
WO 96/07886 PCT/US95/10550
z1 ~~ssg , .
11
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded view of a gas analyzer
comprising: (a) an airway adapter type of cuvette
which embodies the principles of the present invention
and which provides a particularized flow path for a
gas being analyzed, and (b) a transducer which gener-
ates a beam of infrared radiation, propagates that
beam along an optical path traversing the cuvette flow
path, detects the beam as attenuated by a designated
gas in the flow path, and outputs a signal indicative
of the concentration of the designated gas;
FIG. 2 is a section through the airway
adapter/transducer assembly;
FIG. 3 is an exploded view comprised of: a
transverse section through the airway adapter; one of
two windows which transmit infrared radiation to the
airway adapter flow passage and, after it has been
attenuated by the designated gas, from the flow
passage to the exterior of the airway adapter; and a
retainer which holds the window in place in the body
of the airway adapter;
FIG. 4 is a simplified view of one machine
that can be used to install the windows and retainers
in the airway adapter of FIG. 1 and to seal the gaps
between the retainers and the apertures in which they
are installed;
FIGS . 5 is a fragmentary section through the
airway adapter showing one of its radiation transmit
ting windows in an initial stage of being installed
with the technique depicted in FIG. 3 and the machine
illustrated in FIG. 4;
WO 96/07886 PCT/US95/10550
J >. _f ., s~., ~,
12
FIG. 6 is a view like FIG. 5 but showing the
window completely installed;
FIG. 7 is a simplified vertical section
through a second gas analyzer with a cuvette which
also embodies the principle of the present invention;
FIG. 8 is a top view of the cuvette of FIG.
7:
FIG. 9 is a view like FIG. 7 of a third gas
analyzer with a cuvette which embodies the principles
of the present invention;
FIG. 10 is a top view of the cuvette shown
in FIG. 9;
FIG. 11 is a fragment of FIG. 4 to an
enlarged scale;
FIG. 12 is a perspective view of a sampling
airway adapter employing the principles of the present
invention;
FIG. 13 is a second perspective view of the
sampling airway adapter; and
FIG. 14 is a section through FIG. 12 taken
substantially along line 14-14 of the latter figure.
WO 96/07886 PCT/US95/10550
219888
13
DETAILED DESCRIPTION OF THE INVENTION
Referring now the drawing, FIGS. 1 and 2
depict a gas analyzer 20 composed of: (1) an airway
adapter 22 embodying the principles of the present
invention and designed for connection between an
endotracheal tube inserted in a patient's trachea and
the plumbing of a mechanical ventilator; and (2) a
complementary transducer 24 for outputting: (a) a
signal proportional in magnitude to the concentration
of carbon dioxide flowing through airway adapter 20,
and (b) a reference signal. These signals can be
ratioed in the manner disclosed in the above-cited
'858, '859, and '436 patents to provide a third signal
accurately and dynamically representing the concentra-
tion of the carbon dioxide flowing through the airway
adapter.
FIG. 1 shows primarily the polymeric hous-
ing 26 of transducer 24. The transducer also includes
an infrared radiation emitter unit or source 28 and a
detector unit 30 (see FIG. 2).
That casing 26 of transducer 24 in which the
infrared radiation emitter unit 28 and detector
unit 30 are housed has first and second end
sections 32 and 34 with a rectangularly configured
gap 36 therebetween. With the transducer assembled to
airway adapter 22, the two sections 32 and 34 of
transducer casing 26 embrace airway adapter 22,
integrating the adapter and transducer into a single,
easily handled unit or assembly.
Optically transparent windows 38 and 40 are
installed in transversely aligned apertures 42 and 44
provided in the inner end walls 46 and 48 of transduc-
WO 96/07886 PCT/US95/10550
,F _,
14
er housing 26. These windows allow the beam 49 of
infrared radiation generated in unit 28 in the left-
hand end section 32 of transducer housing 26 to pass
along optical path 50 to airway adapter 22 and from
the airway adapter to the detector unit 30 in the
right-hand section 34 of the transducer housing. At
the same time, windows 38 and 40 keep gases from
escaping and keep foreign material from penetrating to
the interior of the transducer casing.
1o Unit 28 is employed to emit infrared radia-
tion, to form that energy into beam 49, and to propa-
gate the beam along the optical path 50 traversing the
gas being monitored as it flows through airway adapter
22. Unit 20 includes: (1) a thick film infrared
radiation emitter 52, (2) an emitter protecting
cap 54, (3) a parabolic, gold-over-copper-plated
mirror 56 for collating the energy outputted from
emitter 52, and (4) an emitter-, mirror-, and cap-
supporting base 58.
Detector unit 30 includes a boxlike housing
60 mounted on a printed circuit board 62. A monolith-
ic, heat conductive, isothermal support 64 is in-
stalled in housing 60. Supported from and mounted in
support 64 are: (1) data and reference detectors 66
and 68 , ( 2 ) a beam splitter 70, ( 3 ) detector heaters
72 and 74, and (4) a thermistor-type current flow-
limiting device 76. The system in which heaters 72
and 74 and thermistor device 76 are incorporated (see
above-cited patent No. 5,153,436) is employed to keep
the reference and data detectors 68 and 66 at the
same, selected temperature, typically with a tolerance
of not more than 0.01°C.
WO 96!07886 PCT/US95110550
~1 ~~~$9 , v
Detectors 66 and 68 are preferably fabricat
ed with lead selenide detector elements because of the
sensitivity which that material possesses to electro
magnetic energy having wavelengths which are apt to be
5 of interest.
Each of the two detectors 66 and 68 is
mounted in a stepped recess 78 opening onto the front
side of heat conductive support 64. A gap 80 around
the periphery of the detector and between the detector
10 and isothermal support 64 electrically isolates the
detector from the also conductive, isothermal support.
Beam splitter 70 has a generally parallel
epipedal configuration. This component is fabricated
from a material such as silicon or sapphire which is
15 essentially transparent to electromagnetic energy with
wavelengths of interest. The exposed front surface 82
of the beam splitter is covered with a coating 84
which will ref lect to data detector 66 as indicated by
arrow 86 in FIG. 2 energy having a wavelength longer
than about 4 microns. The energy of shorter wave-
lengths is, instead, transmitted through the beam
splitter to reference detector 68 as is suggested by
arrow 88 in the same figure.
Bandpass filters 90 and 92 limit the elec
tromagnetic energy respectively reflected from and
transmitted by beam splitter 70 and impinging upon
detectors 66 and 68 to energy in selected bandwidths.
Reference detector filter 92 in detector unit 30 is
centered on a wavelength of 3.681 ~cm and has a half
power bandwidth of 0.190 ~cm. The data detector
bandpass filter 90 is centered on a wavelength of
4.260 ~Cm and has a bandwidth of 0.10 ~,m. This is two
times narrower than the band passed by filter 92. The
WO 96/07886 PCT/US95/10550
21988:88r- - « w
16
carbon dioxide absorption curve is fairly narrow and
strong, and bandpass filter 90 centers the transmis-
sion band within that absorption curve. Therefore, if
there is a change in carbon dioxide level in the
gases) being analyzed, the maximum modulation for a
given change in carbon dioxide level is obtained.
Each of the bandpass filters 90 and 92 is
installed in that stepped recess 78 in monolithic,
isothermal support 64 in which the associated detector
66 or 68 is mounted.
The upper edge 94 of beam splitter 70 is
fitted into a recess 96 in monolithic, isothermal
support 64 midway between the bandpass filter 90 in
front of data detector 66 and the bandpass filter 92
in front of reference detector 68. The opposite,
lower part 98 of the beam splitter is fixed to an
inclined, integral lip 100 which extends inwardly from
detector unit casing 60.
The electromagnetic energy in beam 49
reaches beam splitter 70 through an aperture 102 in
the front side of detector unit casing 60. A sapphire
window 104 spans aperture 102 and keeps foreign
material from penetrating to the interior of housing
60.
To exclude extraneous energy, and thereby
ensure that only the energy in beam 49 reaches beam
splitter 70, light traps 106 and 108 are provided.
The first of these is a triangularly sectioned,
inwardly extending projection of monolithic isothermal
support 64. The second, cooperating light trap 108 is
aligned with, fixed in any convenient fashion to, and
extends inwardly from the casing-associated ledge 100
supporting beam splitter 70.
WO 96107886 PCT/I1S95/10550
~~~..r r.
17
The operation of transducer 24 is believed
to be apparent from the drawings and the foregoing,
detailed description of the transducer. Briefly,
however, electromagnetic energy in the infrared
portion of the spectrum is generated by heating the
source or emitter 52 of emitter unit 28, preferably by
applying bipolar pulses of electrical energy to the
emitter unit. The energy thus emitted is propagated
toward the concave, emitter unit mirror 56 as shown by
arrow 110 in FIG. 2. Mirror 56 collimates and focuses
this energy and propagates it in the form of beam 49
along optical path 50 across the gases) flowing
through airway adapter 22.
Energy in a species specific band is ab
sorbed by the gas of interest flowing through the
airway adapter (typically carbon dioxide) to an extent
proportional to the concentration of that gas.
Thereafter, the attenuated beam passes through the
aperture 102 in detector unit casing 60, is intercept
ed by beam splitter 70, and is either reflected toward
data detector 66 or transmitted to reference detector
68. The bandpass filters 90 and 92 in front of those
detectors limit the energy reaching them to specified
(and different) bands. Each of the detectors 66 and
68 thereupon outputs an electrical signal proportional
in magnitude to the intensity of the energy striking
that detector. These signals are amplified and then
ratioed to generate a third signal accurately reflect-
ing the concentration of the gas being monitored. The
signal processor used for this purpose is independent
of airway adapter 22 and transducer 24, is not part of
the present invention, and will accordingly not be
disclosed herein.
WO 96107886 PCT/US95/10550
219888~.:~: .,.:
18
Resistance heaters 72 and 74 and thermistor
76 are installed in isothermal support 64, producing
efficient, conductive heat transfer between the
heaters and the support. The spatial relationship
between heater 72 and data detector 66 and between
heater 74 and reference detector 68 are identical, and
the spatial relationship between thermistor 76 and
each of the heaters 72 and 74 is also identical.
Furthermore, the two heaters 72 and 74 are so located
with respect to the associated detectors 66 and 5R
that the thermal energy emitted from the heaters
travels first across the detectors and then across the
current flow-limiting thermistor 76 to heat dumps
provided by gaps 118 and 120 between isothermal
support 64 and detector unit housing 60 (The heat flow
paths are identified by arrows 122 and 124 in FIG. 2).
As a consequence of the foregoing and the high thermal
conductivity of isothermal support~64, the data and
reference detectors 66 and 68 can readily be main-
tained at the same temperature as is required for
accuracy of gas concentration measurement.
Referring more specifically to FIGS. 1-3,
airway adapter 22 embodies the principles of the
present invention and is typically molded from a
polycarbonate or a comparable rigid, dimensionally
stable polymer. The airway adapter has a generally
parallelepipedal center section 126 and two cylindri-
cal end sections 128 and 130 with a sampling (or flow)
passage 132 extending from end-to-end through the
adapter. Left-hand and right-hand airway adapter end
sections 128 and 130 are axially aligned with center
section 126.
WO 96107886 PCT/US95/10550
2198889-''
19
The central section 126 of airway adapter 22
provides a seat for transducer 24. An integral,
U-shaped casing element 134 positively locates trans-
ducer 24 endwise of the adapter and, also, in that
transverse direction indicated by arrow 136 in FIG. 1.
That arrow also shows the direction in which airway
adapter 22 is displaced to detachably assemble it to
transducer 24. The airway adapter snaps into place
(see the above-cited '858 and '859 patents); no tools
are needed to assemble or _remove the adapter.
Aper-tures 138 and 140 are formed in the
center section 126 of airway adapter 22. With trans-
ducer 24 assembled to the airway adapter, these
apertures are aligned along optical path 50. Thus,
infrared radiation beam 49 can travel from the infra-
red radiation emitter unit 28 in transducer 24 trans-
versely through airway adapter 22 and the gases)
flowing through airway adapter flow passage 132 to the
infrared radiation detector unit 30 of transducer 24.
To: (a) keep the gases flowing through
airway adapter sampling passage 132 from escaping
through apertures 138 and 140 without attenuating the
infrared radiation traversing optical path 50, and
(b) keep foreign material from the interior of the
airway adapter, the apertures 138 and 140 are sealed
by windows 142 and 144 which have a high transmittance
for radiation in the infrared portion of the electro-
magnetic spectrum.
As discussed above, that casing 26 of
transducer 24 in which the source unit 28 and detector
unit 30 are housed has first and second end
sections 32 and 34 with a rectangularly configured
gap 36 therebetween. With the transducer assembled to
WO 96!07886 PCT/US95/10550
airway adapter 22, the two sections 32 and 34 of
transducer casing 26 embrace those two inner side
walls 146 and 148 of airway adapter central
section 126 in which energy transmitting windows 142
5 and 144 are installed. This securely attaches airway
adapter 22 to transducer 24 with airway adapter
windows 142 and 144 and transducer windows 38 and 40
all aligned along optical pathway 50, allowing infra-
red radiation beam 49 to travel from emitter unit 28
10 to detector unit 30 through the gases) in sampling
passage 132.
Heretofore, the windows of cuvettes such as
that shown in FIGS. 1-3 as well as cuvettes of other
configurations have been fabricated from sapphire
15 because of that material's favorable optical proper-
ties; stability; and resistance to breakage, scratch-
ing, and other forms of damage. However, as dis-
cussed above, sapphire windows are expensive; and this
makes it impractical to discard the cuvette after it
20 is used to monitor a single patient. Instead, the
cuvette must be cleaned, sterilized, and reused, which
is inconvenient and often perceptually hazardous.
It has now been found that the cost of
manufacturing a cuvette can be reduced -- even to the
point of making it practical to dispose of the cuvette
after a single use -- by fabricating the cuvette
windows from an appropriate polymer rather than the
many times more expensive, heretofore employed sap-
phire.
It is essential to accuracy that the polymer
transmit a usable part of the infrared radiation
impinging upon it. As discussed above, the preferred
window material is biaxially oriented polypropylene.
CA 02198889 2002-11-26
21
Referring now specifically to FIGS, 2, 3, 5 and 6, windows
142 and 144 are installed in airway adapter apertures 138 and 140
such that the inner surfaces 150 and 152 of the windows are flush
with the inner surfaces 154 and 156 of airway adapter center section
side walls 146 and 148. This eliminates any recesses in optical path
apertures 138 and 140 in which debris might collect and obscure the
optical aperture. The flush-mounting also minimizes flow resistance
and assures that there are no edges which would interfere with the
delivery of medication or the introduction of catheters or other
cannula through the airway adapter.
The perimeters 162 and 164 of. the two window-receiving
apertures 138 and 140 have a configuration which is designed to
position the energy transmitting window 142 or 144 in its aperture
138 or 140 with the window in the above-discussed flush relationship
with the inner surface (154 or 156) of the airway adapter side wall
in which the aperture is formed. Aperture 140 is typical. The
perimeter 164 of aperture 140, which is shown to an enlarged scale
in FIGS. 5 and 6, has an inner segment 1..66. That segment tapers
inwardly (toward the centerline 168 of aperture) from: (1) a plane
170 lying between and parallel to the inner land outer surfaces 156
and 172 of airway adapter side wall 148, t.o (2) the inner side wall
surface 156. A second, integral segment 174 of the aperture tapers
inwardly (also toward aperture centerline 168) over that span lying
between plane 170 and outer side wall surface 172.
Windows 142 and 144 are held in place (or
immobilized) in the associated apertures 138 and 140
WO 96/07886 PCT/US95/10550
2198889
22
in the flush-mounted relationship just described with
skeletal, elastically compressible, snap-in retainer
rings 176 and 178, which are typically made from
brass. Brass has the advantage that it is cheap,
easily machined, and readily plated with other metals
such as nickel, if desired. However, other materials
may be employed in place of brass although many
polymers are not suitable as they would not be able to
withstand the forces generated during the installation
of the retainers.
The two retainers 176 and 178 are identical;
accordingly, only retainer 178, best shown in FIGS. 5
and 6, will be described in detail. That airway
adapter component has a circular configuration. Its
periphery has a first, inner segment 180 which comple-
ments the inner segment 166 of window aperture perime-
ter 164; like the latter, it is tapered toward aper-
ture centerline 168 from plane 170 to airway adapter
inner side wall surface 156. The ring also has an
integral, outer segment 182 complementing the outer
segment 174 of the aperture 140 perimeter. That
retainer ring segment tapers toward aperture center-
line 168 from plane 170 to airway adapter side wall
outer surface 174. -
By virtue of the complementary configura-
tions just described, retainer ring 176 snaps into
aperture 140. It is thereby positively retained in
that exact location shown in FIG. 6 in which it
retains window 144 in aperture 140 in the flush
relationship to airway adapter inner wall surface 156
described above.
Referring now most specifically to FIGS. 3,
5, and 6, the initial step in installing window 144 is
WO 96/07886 PCT/US95110550
..
23
to die cut or otherwise form a circular blank 184 from
an appropriately thick sheet of the selected infrared
radiation transmitting polymer. As shown in FIG. 3,
blank 184 and retainer ring 176 are positioned adja-
cent airway adapter side wall 160 in axial alignment
with and centered along the centerline 168 of aperture
140. The blank and retainer ring are then displaced
toward airway adapter 22 and into aperture 140 as
indicated by arrow 186 in FIG. 3. As blank 184 and
retainer ring 176 are forced through aperture 140
toward sampling passage 132, the margin 188 of blank
184 -- particularly if the blank is made from a
malleable polymer as is preferred -- is molded first
around the inner segment 180 of retainer ring 178 (see
FIG. 5) and then around the outer segment 182 of the
retainer ring (see FIG. 6). This results in the
marginal segment 188 of the blank forming a gastight
seal in the gap 190 between the perimeter 164 of
aperture 140 and the periphery of retainer ring 178
when the blank and retainer ring reach the assembled,
or final, FIG. 6 position. At the same time, the
rigidity and toughness of the material and the just
described installation process result in the window
segment 140 of the blank being placed under tension
and therefore being flat and free of distortions which
might produce an error in the signal outputted by
transducer 24.
One machine for forming blank 184 and for so
pressing that blank and retainer ring 178 into aper-
ture 140 as to form and immobilize window 144 with the
retainer ring snapped into place and the gap 190
between it and the perimeter 164 of aperture 140
sealed is illustrated in FIGS. 4 and 11 and identified
CA 02198889 2002-11-26
24
by reference character 192. That machine includes an airway
adapter-supporting mandrel 194, a die 196 and a hollow punch 198
supported by a second mandrel 200 for movement in the arrow 186 and
opposite directions (the same machine is of course used to form and
install window 142 and retainer ring 176?.
Airway adapter-supporting mandrel 194 is dimensioned and
configured to match the sampling passage x.32 through airway adapter
22. This mandrel is employed to position the airway adapter with
aperture centerline 168 in axial alignment with the longitudinal
centerline 201 of die 196 and punch 198. The mandrel also backs up
the side wall 148 of the airway adapter as the window forming blank
184 and retainer ring 178 are pressed into the aperture.
Mandrel 200 is mounted to machine framework 203. An
integral annular stop 202 and a frame-associated stop 204 immobilize
airway adapter 22 in the illustrated and just described window
installation position relative to punch 196.
Die 196 is a hollow, stationary, cylindrical component
mounted along centerline 168a and operationally located adjacent the
airway adapter 22 in which windows are being installed., A slot 205
extending through the wall 206 of the die at right angles to
centerline 168a accommodates a rectilinearly displaceable strip 207
of window-forming polymer. An integral, annular ledge 208 extending
inwardly from die wall 206 into longitudinally extending central bore
209 immediately above slot 205 defines one of two cooperating cutting
edges 210 for severing blank 184 from strip 207. The second cutting
edge is formed on punch 198 and :is described below.
CA 02198889 2002-11-26
Mandrel-supported, hollow punch 198 is an elongated tube.
It is dimensioned for a free sliding fit in; (1) the :lower segment
212 of the longitudinally extending bore 209 through die 196 and (2)
an axially aligned bore 214 through a stationary, punch-and-die
5 supporting component 216 of machine 192. The die-associated end
segment 218 of punch 198 is tapered outwardly to complement the
configuration of retaining ring peripheral outer segment 182. The
sharp cutting edge 219 at the free end of punch segment 218
cooperates with the cutting edge 210 of die 196 to sever blank 184
10 from strip 207 as punch 198 ~.s displaced relative to die 196 in the
arrow 186 direction.
Punch-supporting mandrel 200 is fixed in any appropriate
fashion to tubular punch 198 and is displaced in the arrow 186 and
opposite directions by a mechanism which has not been shown as it is
15 not part of the present invention. The die facing end 220 of mandrel
200 lies inwardly from the cutting edge 219 of punch 198. This
leaves an open recess or cavity 221 for retainer 178. The upper edge
222 of the retainer lies below cutting edge 219 and will not
interfere with the cutting blank 184 from strip 207.
20 Mandrel 200 has a vacuum system including a central cavity
224 opening onto the die facing end 220 of the mandrel and an
internal vacuum line 226 providing fluid communication between cavity
224 and a vacuum pump (not shown). A porous plug 228, fitted into
vacuum cavity 224, promotes a uniform negative pressure profile at
25 the die-facing end of cavity 224 and r:~onsequently, a similarly
uniform negative pressure profile over the area of the hollow bore
230 through retainer ring 17a.
WO 96!07886 PCT/US95/10550
26
The vacuum system just described and identi-
fied in its totality by reference character 232 is
employed to hold the window-forming blank 184 on and
in axial alignment with the retaining ring 178 in-
s stalled in cavity 221 as punch 198 and the retaining
ring 178 are displaced further in the arrow 186
direction to press the blank and retaining ring into
aperture 140.
Installation machine 192 is shown in FIG. 4
l0 at the beginning of its operating cycle with retainer
ring 178 having been placed in cavity 221 from the
open upper end of the bore 209 in die 196 by dropping
it through that bore, the hole 234 left by punching
the preceding blank from strip 207, and the lower part
15 212 of die bore 209, care being taken to ensure that
the retainer ring is placed in recess 221 in the
orientation shown in FIG. 4. Thus installed in recess
221, retainer ring 178 is seated on the upper end 220
of mandrel 200 and backed against deformation during
20 the installation process. The upper edge 222 of the
retainer lies in the recessed, non-interfering rela-
tionship with the cutting edge 184 of punch 198. A
protruding, annular, hollow boss 238 at the upper end
220 of die 196 centers retainer ring 178 about axial
25 centerline 201, precisely aligning the retainer ring
with the aperture 140 in which it is to be installed.
The assembly of mandrel 200 and punch 198 is
then advanced in the arrow 186 direction with the
cutting edges 210 and 219 of die 196 and punch 198
30 severing blank 184 from strip 206 and vacuum system
232 trapping the blank on the upper end segment 218 of
the punch in axial alignment with retainer ring 178.
W0 96107886 .' > PCT/US95/10550
., Y
27
As punch 198 continues through and beyond
die 196 in the arrow 186 direction, blank 184 and
retainer ring 178 are pressed into aperture 140. This
tensions and eliminates distortions in the window-
s forming portion of the blank and begins the seal-
forming deformation of blank 184 by virtue of periph-
eral blank segment 188 being trapped against the outer
edge segment 174 of aperture boundary 164 (FIG. 5).
Continued movement of the punch 198 in the arrow 186
direction: (1) completes the formation of the seal
188 in the gap_ 190 between the boundary of aperture
140 and the periphery of retainer ring 178 and the
elimination of distortions in the window-forming
material, (2) displaces the window-forming segment 144
of the blank into the above-discussed flush-mounted
relationship with the inner, sampling passage-defining
surface 156 of airway adapter side wall 160; and (3)
snaps retainer 178 into place to positively retain the
window in place (see FIG. 6). If blank 184 is fabri-
Gated from the preferred material, the seal 188 is
formed without wrinkling, creasing, folding, or
puckering of the material and without that material
being sheared by the retainer. This promotes gastight
sealing of the gap 190 between the retainer 178 and
the aperture 144 in which it is installed.
Finally, punch 198 and mandrel 200 are
retracted to the illustrated position to ready machine
192 for the next installation cycle.
It was pointed out above that there are many
cuvettes in which polymeric, infrared radiation
transmitting windows may be employed to advantage in
accord with the principles of the present invention.
One of these is discussed above; and it may be manu
WO 96/07886 PCT/US95/10550
2198889
28
factured in different sizes suiting it for adult,
neonatal, and other applications. A second such
cuvette and the folded path gas analyzer in which it
is employed are shown in diagrammatic form in FIGS. 7
and 8 and identified by reference characters 240 and
242, respectively.
Cuvette 242 has top and bottom walls 244 and
246 fabricated of a porous, particulate material
trapping polyethylene or other material with suffi-
cient structural integrity and dimensional stability
to positively locate with a precise distance therebe-
tween two radiation transmitting windows 248 and 250
embodying the principles of the present invention as
elucidated above. These windows may be assembled to
cuvette walls 244 and 246 and the gaps between the
windows and the walls sealed with retainer rings of
the character described above. To this end, recesses
252 and 254 formed in cuvette top and~bottom walls 244
and 246 and opening onto the opposite sides 256 and
258 of the cuvette have V-shaped boundaries as dis-
cussed above and best shown in FIGS. 5 and 6 which
cause the retainer rings 264 and 266 to snap into
place as they are pressed into the apertures.
Cuvette top and bottom walls 244 and 246,
windows 248 and 250, and the side walls 268 and 270 of
gas analyzer housing 272 cooperate to define a sam
pling passage 274 for the gas being monitored.
Cuvette 242 is installed in gas analyzer
housing 272 between its left-hand and right-hand ends
276 and 278. Mounted in a thus defined right-hand
compartment 280 are an infrared radiation emitter unit
281 and an infrared radiation detector unit 282 which
may be of the character shown in FIG. 2 and discussed
WO 96107886 PCT/US95110550
29
above. Mounted in a complementary left-hand end
compartment 284 are infrared radiation-reflecting
mirrors 286 and 288.
Infrared radiation generated by emitter unit
281 is formed into a beam 49 as in the unit 28 depict
ed in FIG. 2. Beam 49 is propagated along the first
leg 289 of an optical path 290 through cuvette window
250, the gases) in cuvette sampling passage 274, and
cuvette window 248 to mirror 286. The beam of radia
tion is attenuated as it passes through cuvette 242 to
an extent proportional to the concentration of the gas
being monitored.
Mirror 286 turns the beam of infrared
radiation 90 degrees, causing it to travel along the
second leg 292 of optical path 290 to the second of
the infrared radiation reflecting mirrors 288. That
mirror turns the beam 90 another degrees. This causes
the beam to travel along a third optical path leg 294
in a direction opposite to that in which it was
initially propagated through: cuvette window 248, the
gases) in cuvette sampling passage 274, and cuvette
window 250 to infrared radiation detector unit 282,
the gas again being attenuated to a degree proportion-
al to the concentration of the gas being monitored.
The twice attenuated beam of infrared
radiation is intercepted by detector unit 282 which
consequentially outputs an electrical signal indica-
tive of the concentration of the monitored gas.
Gas analyzer 240 is designed to monitor
gases which reach cuvette 242 through one of the two
ports 296 and 298 in gas analyzer casing side walls
268 and 270. These gases enter the sampling passage
274 in cuvette 242 and exit from that passage through
WO 96!07886 PCT/US95I10550
2198889
the porous cuvette top and bottom walls 246 and 244 as
indicated by double-headed arrow 300 in FIG. 7.
This type of gas analyzer can be employed to
advantage as one example to monitor gases in rooms,
5 buildings, and other confined spaces. Gas analyzer
240 has the advantage of being compact, and it can be
produced at lower cost by virtue of its employing
polymeric windows rather than the customary sapphire
for transferring infrared radiation into and out of
10 cuvette 242.
Referring still to the drawings, FIGS. 9 and
10 depict a folded path gas analyzer 304 which differs
from the analyzer 240 just discussed primarily by the
addition of tubular fittings 306 and 308. These
15 fittings communicate with ports 296 and 298 in the
side walls 268 and 270 of gas analyzer housing 272.
Gas analyzer 304 is employed in medical and
other applications where recirculation of the gases)
introduced into sampling passage 274 is required or
20 advantageous and/or where positive circulation as
opposed to connective or diffusive flow of the gases)
through the sampling chamber is dictated. The com-
pactness and light weight of gas analyzer 304 is
particularly beneficial in in-line applicat-ions such
25 as end tidal carbon dioxide monitoring because it can
be located close to the patient's face, which is out
of the way and promotes accuracy.
Cuvettes of the diffusion/convective and
positive flow types just described above and illus
30 trated in FIGS. 7-10 can vary considerably from the
specific, exemplary configurations shown in the
drawings. For example, they may be constructed with
CA 02198889 2002-11-26
31
a porous, gas transmitting wall which extends all the way around the
radiation transmitting windows.
Yet another cuvette embodying the principles of the present
invention is the sampling airway adapter illustrated in FIGS. 12 -
14 and identified by reference character 312. The particular adapter
depicted in the drawings is molded from a polysulfone. However, it
may equally well be manufactured from a polycarbonate or a comparable
polymer.
Cuvette 312 has a center section 314 and hollow,
cylindrical, left-hand and right-hand end sections 316 and 318. An
integral platform 320 of cuvette center section 314 provides a seat
for a transducer such as that depicted in FIG. 1 and identified by
reference character 24. An integral, U-shaped casing element 322
positively locates the transducer endwise of cuvette 312 and also in
that transverse direction indicated by arrow 324 in FIG. 13. Arrow
326 in the same Figure shows the direction in which the transducer
is displaced to detachably assemble it to cuvette 312. The airway
adapter snaps into place (see the above-cited '858 and '859 patents)
and no tools are needed to assemble or remove the adapter.
As is best shown in FIG. 14, a transversely oriented,
frustoconically sectioned sampling chamber 328 is formed in the
central section 314 of cuvette 312. The gas being sampled flows in
the direction indicated by arrow 330 in F:~G. 14 through the hollow
bore 332 of the cuvette's .left-hand end section 316 to the sampling
chamber where the concentration of a particular specie such as carbon
dioxide is measured, using the non-dispersive infrared radiation
technique discussed above. Thereafter, the sample is discharged
WO 96!07886 PCT/US95/10550
~I~8889
32
from chamber 328 through a communicating passage 334
in the central cuvette section 314 and the hollow bore
336 of right-hand cuvette section 318 as suggested by
arrow 338.
Apertures 340 and 342 are formed in, and on
opposite sides of, the center section 314 of cuvette
312. With a transducer of the type depicted in FIG.
1 assembled to cuvette 312 these apertures are aligned
along optical path 344. Thus, infrared radiation
outputted from the emitter unit in the transducer can
travel in the arrow 344 direction through sampling
passage 328 and the gas or gases therein to the
detector unit of the transducer.
To: (a) keep the gases in sampling chamber
328 from escaping through apertures 340 and 342
without attenuating the infrared radiation traversing
optical path 344, and (b) keep foreign material from
the interior of cuvette 312, apertures 340 and 342 are
sealed by windows 346 and 348 which have a high
transmittance for radiation in the infrared portion of
the electromagnetic spectrum. As in the cuvettes
discussed above, windows 346 and 348 are fabricated
from an appropriate polymer, preferably a biaxially
oriented polypropylene. Windows 346 may be formed,
installed, and retained in place with skeletal retain-
ers 350 and 352 of the character discussed above or by
any other appropriate technique.
The invention may be embodied in many forms
without departing from the spirit or essential charac
teristics of the invention. The present embodiments
are therefore to be considered in all respects as
illustrative and not restrictive, the scope of the
invention being indicated by the appended claims
WO 96/07886 PCTIUS95/10550
z1 ~sss
33
rather than by the foregoing description. All changes
which come within the meaning and range of equivalency
of the claims are therefore intended to be embraced
therein.
