Note: Descriptions are shown in the official language in which they were submitted.
S WO 94/17848 ~ ~ ~ ~ ~ ~ PCT/GB93100578
ARTIFICIAL AIRWAY DEVICE
Backctround of the Invention
This invention relates to an artificial airway device
- to facilitate lung ventilation in an unconscious patient,
and
more specifically to such a device designed for placing in
the oropharynx of the patient in order to prevent airway
obstruction, to permit either spontaneous or controlled
ventilation and to prevent the inhalation into the lungs of
extraneous matter such as blood.
To maintain the airway of an unconscious patient, and
to achieve the three obj ectives mentioned above, it is normal
practice in general anaesthesia to use an endotracheal tube,
which is a flexible tube of rubber or plastics, usually with
an inflatable cuff around the distal end.. Alternatively,
an
oro- or naso-pharyngeal airway may be used, which is a
flexible tube extending from the mouth or nose into the
pharynx but not into the larynx, and which, unlike the
endotracheal tube, is used in conjunction with a face mask.
While preventing obstruction of the airway by the tongue,
the
oro- or naso-pharyngeal airway cannot conveniently be used
for controlled ventilation and does not prevent inhalation
of extraneous matter.
The endotracheal tube is introduced through the larynx
into the trachea or windpipe, whereupon the cuff is inflated
through a small auxiliary tube to seal against the wall of
the trachea. Introduction of the endotracheal tube is a
skilled operation normally requiring use of a laryngoscope
to guide the tube through the larynx, past the vocal cords
and into the trachea. There is a risk that the tube or the
laryngoscope may cause damage to soft tissues or to the
sensitive structures of the larynx. It is not always
possible to see the larynx, making intubation difficult or
impossible in some patients. There can be a risk of
accidental intubation of the oesophagus or of the right or
left main bronchus. Placing of the tube in the trachea
WO 94/17848 PCT/GB93/00578
2
effectively narrows the interior passage or lumen of the
trachea and provides a potential source of damage through
infection or pressure while preventing normal upward flow of
mucus from the trachea and rendering effective coughing
impossible.
My British Patent Specification No. 2111394B describes
an artificial airway device comprising a curved or flexible
tube and a mask portion carried at one end of the tube. The
mask portion has a flexible annular peripheral formation
which may be inflatable and which surrounds a hollow interior
space or lumen of the mask portion. Said annular peripheral
formation of the mask portion is pre-formed with a roughly
elliptical shape so as to be capable of conforming to, and
of fitting readily within, the actual and potential space
behind the larynx, thereby forming a seal around the
circumference of the laryngeal inlet without having the
device penetrate into the interior of the larynx. The tube
opens into the lumen of the mask portion to provide the
airway, with the axis of the tube at an acute angle to the
general plane of the annular peripheral formation and
substantially aligned with the major axis of the roughly
elliptical shape of the annular peripheral formation of the
mask portion. The device thus constitutes a laryngeal mask.
This device has proved successful in use. Insertion of
the device has been found to be easy and convenient in the
majority of patients. A laryngoscope is not usually
required. The mask does not enter the larynx or trachea, so
the risk of damage to these structures is avoided and the
tracheal lumen is not narrowed, as is the case upon insertion
of an endotracheal tube. The risk of accidental entry into
the oesophagus or one of the main bronchi is also avoided. '
Once in place, the laryngeal mask generally permits the lungs
. to be ventilated by positive pressure. Alternatively, the
patient may be permitted to breathe spontaneously.
~WO 94/17848 ~ ~ ~ PCT/GB93100578
3
An improved laryngeal mask is described in my Patent No.
GB 2,205,499B, in which there are provided two flexible
cross-bars extending across the aperture in the peripheral
annular flexible formation. These bars preferably extend
substantially parallel with the major axis of the generally
elliptical annular formation. As this patent explains, the
parallel bars serve to prevent the epiglottis from blocking
the airway passage of the mask.
In the existing laryngeal mask, the peripheral seal
formation is an inflatable annulus which, when inflated, is
a generally elliptical toroid. Its manufacture presents
difficulties, in that the process uses a so-called "floating
core" within the outer or female part of the mould. This
core is supported by a relatively small pin which ultimately
defines the bore of the inflation inlet but which must
maintain uniform spacing from the adjacent wall surface of
the female mould. It is desired that the wall of the moulded
annulus be uniformly thin', for example, a selected single
thickness in the range 0.4 to 1.0 mm, preferably 0.7 mm. In
practice, however, injection of liquid rubber into the mould
is under high pressure, and the "floating core" support pin
is not capable of resisting small displacements which can
cause thickness variations in the wall of the moulded
product. In consequence, it has been necessary to maintain
a relatively thick wall in the peripheral annular formation
so that small changes in wall thickness produced by movement
of the core during injection will not result in deformity or
rupture of the device when air-inflated in the course of use.
The difficulty with a relatively thick wall is that the
3o inflatable annulus is less compliant in adapting itself to
the contours of the human pharynx and larynx, thus reducing
Thin, for greatest flexibility in establishing the intended
peripheral seal to the laryngeal inlet; and uniformly thin,
to avoid weak areas that might invite herniation.
~1~~11~
WO 94/17848 PCT/GB93/00578
4
the efficacy of the desired seal to the laryngeal inlet,
and/or unduly limiting the pressure which it is possible to
f
use for inflation of the lungs without loss of seal.
A further disadvantage of the existing manufacturing
process is that it is highly labor-intensive, since the
tubular airway portion of the device to which the peripheral
annular formation is attached must be connected via a third
part, or back plate. This third part is separately moulded
and forms an appropriate shape at one end to fit Within the
peripheral annular formation and at the other end to receive
the tubular airway portion of -the device. Finally, the back
plate and the cut inner periphery of the inflatable ring must
be so adhesively secured as to complete the inflatable
integrity of the ring as well as the sealing effectiveness
of the back plate to the inflatable ring.
RriPf Statement of the Invention
The primary object of the present invention is to
provide a manufacturing process which will avoid the unwanted
movement of the mould core, thus permitting the manufacture
of a peripheral annular formation with a significantly
thinner wall, with greater precision and at lower cost.
Another object is to meet the above object with a
process which lends itself to integrally connected moulding
of the inflatable ring and back plate components of the mask
in a single operation.
A further object is to meet the above objects with a
process which further lends itself to integrally formed
provision for an oesophagus-drainage feature in the mask
3 0 structure .
The invention achieves these objects by providing a
mould which is designed to produce a peripheral annular
formation substantially identical to that described in my UK '
Patent No. GB 2,205,499B, but in an inverted form. The
moulded part must therefore be inverted before it takes up
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the desired shape. This inversion is readily achieved
provided the part is manufactured from flexible plastic or
rubber material or any material which will permit inversion
by virtue of its flexibility. The advantage of
5 manufacturing the peripheral annular formation in its
inverted form is that the core of the mould required to form
this shape does not "float" because, instead of being fixed
in place by a relatively small pin, it has a large surface
of attachment to remaining parts of the mould. This makes
it possible to manufacture the inflatable part with a much
thinner and more precisely formed wall since variations in
wall thickness are less likely to occur. A further
possibility offered by the technique is the use of the core
to form the inverted component by a dip-moulding process, in
which the core only is dipped into the plastics or rubber
material, in liquid form.
Where techniques other than dip-moulding are used,
the second-stated object of the invention is realized by
eliminating the need for a separate back plate part, in that
the moulded back plate is an integral part of the peripheral
annular formation.
In summary the invention provides a method of
constructing a laryngeal mask wherein a back-plate formation
provides in essentially a single geometric plane an
apertured base-mounting rim of generally elliptical
configuration to otherwise close a ventilation lumen within
an inflatable toroidal ring of flexible material the inner
circumference of which is connected to the periphery of said
rim, said method comprising the steps of: (a) moulding a
skirt of uniformly thin flexible material peripherally
continuously connected at one end to said rim, said skirt
extending away from said rim in an axial direction generally
normal to said plane, said skirt having an outwardly bulging
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5a
body portion and terminating at a lower edge of
substantially the peripheral extent of the connection to
said rims (b) inverting said skirt to the extent of flexibly
defining said ring peripherally continuously around said
rim, with the bulging body of the skirt externally
surrounding said rim and the inverted lower edge of the
skirt downwardly directed within at least a portion of the
inverted bulging body and into proximity with the region of
said one-end connection to said rim; and (c) establishing a
peripherally sealed connection of the inverted lower edge of
the skirt with the region of said one-end connection to said
rim.
From another aspect the invention provides a
laryngeal-mask construction, comprising a back-plate member
providing in essentially a single plane an apertured base-
mounting rim of generally elliptical configuration, and an
inflatable toroidal ring of flexible material the radially
inner circumference of which is connected to the periphery
of said rim, said ring having a generally torioidal wall
with an inner surface and an outer surface, said ring having
a port connection that is locally open through said inner
and outer surfaces, and the inner surface of said wall being
compressionally stressed in opposition to circumferential
tension of the outer surface of said wall.
The invention also provides in a laryngeal mask
construction wherein a backplate member provides in
essentially a single geometric plane an apertured base-
mounting rim of generally elliptical configuration to close
the lumen with an inflatable ring of flexible material the
inner circumference of which is connected to the periphery
of said rim, the improvement in which said inflatable ring
is the product of inverting a pre-molded skirt of uniformly
thin flexible material peripherally continuously connected
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5b
at one end to said rim and extending from said rim to an
axial direction generally normal to said plane, said skirt
having an outwardly bulging body and terminating at a lower
edge of substantially the peripheral extent of the
connection to said rim, the extent in said axial direction
being substantially equal to the circumferential extent of a
section of said ring wherein the section is taken in a
section plane (a) which includes said axial direction, and
(b) wherein the section plane is in a single radial
direction away from said axial direction, said skirt being
inverted to the extent of flexibly defining said ring
peripherally continuously around said rim, with the bulging
body of the skirt externally surrounding said rim and the
inverted lower edge of the skirt downwardly directed within
the inverted bulging body and into peripherally sealed
relation with said one-end connection to said rim.
Detailed Description of the Invention
Preferred embodiments of the invention will be
described in detail in conjunction with the accompanying
drawings. In said drawings:
Fig. 1 is a simplified view in perspective,
showing a two-piece laryngeal mask of the invention, fitted
to the distal end of an airway tube, the aspect being from
the upstream or pharyngeal-cavity side of the mask;
Fig. 2 is a side view in perspective for a first
moulded component part of the mask of Fig. 1, portions being
broken away and in section, wherein the section plane is the
vertical plane of symmetry of the component part;
WO 94/17848 . PCT/GB93/00578
6
Fig. 2A is a sectional view of a second component part
of the mask of Fig. 1, the section plane being the same
vertical plane of symmetry as in Fig. 2;
Fig. 3 is a perspective view of the moulded component
part of Fig. 2 after inverting the lower portion thereof, the
aspect being from the downstream or laryngeal side of the
mask;
Fig. 4 is a simplified section through a mould for
making the component part of Fig. 2;
Fig. 4A is a section in the vertical plane of symmetry
as in Fig. 4, to show a slightly modified moulding-core
element for use in a modified process for making the mask of
Fig. 1;
Fig. 4B is vertical section in the plane of symmetry of
Fig. 4A, and showing the product of moulding pursuant to Fig.
4A, in assembled relation to the back-plate component of Fig.
2A;
Fig. 5 is a side view in elevation showing a one-piece
laryngeal mask of the invention, fitted to the distal end of
an airway tube, a portion being broken-away and in section,
wherein the section plane is the vertical plane of symmetry
of the mask;
Fig. 6 is a view similar to Fig. 2, specific to the
laryngeal mask of Fig. 5;
Fig. 7 is a view similar to Fig. 4, specific to the mask
of Fig. 5;
Fig. 8 is a side view in elevation showing another
laryngeal mask of the invention, fitted to the distal end of
an airway tube, a portion being broken-away and in section,
wherein the section plane is the vertical plane of symmetry
of the mask:
Fig. 9 is a view similar to Figs. 2 and 6, but specific
to the laryngeal mask of Fig. 8; and '
Fig. 10 is a view similar to Figs. 4 and 7, but specific
to the laryngeal mask of Fig. 8.
~WO 94/17848 ~ ~ ~ ~ ~ PCT/GB93/00578
7
Referring initially to the embodiment of Figs. 1 to 4,
the invention is shown in application to an inflatable/
deflatable laryngeal mask 10 fitted to the distal end of an
airway tube 11, which will be understood to be relatively
non-compliant and shaped for manipulated entry of mask 10
into intended position within a patient's pharyngeal cavity,
with the proximal end of tube 11 accessible for ventilation
via or outside the patient's mouth. The mask 11 comprises
a first moulded inflatable/deflatable part (Figs. 2 and 3)
and a second moulded part or back plate 12 (Fig. 2A). In its
completed form, the moulded -part of Fig. 2 establishes a
peripheral inflatable/deflatable element or ring 13 which
is
toroidal and generally elliptical, wherein the distal end
14
is more pointed and the proximal end 15 is more rounded, in
general conformance with similar features of the flat base
rim 16 of back plate 12. The more pointed distal end will
be understood to be for engagement with and location of the
laryngeal mask via the oesophageal inlet, when the elliptical
annulus 13 is poised for inflation, via a suitable air-supply
line connection 17 at the proximal end of the annulus. Also,
consistent with the disclosure of my British patent No. GB
2,205,499B, a flexible membrane 18 closes the lumen of the
mask, all except for a passage established by plural adjacent
openings which define longitudinal bars 19 between openings,
for preventing the epiglottis from blocking the airway
passage of the mask.
In accordance with the invention, the mould (Fog. 4)
that is used to shape the part (Fig. 2), which will
ultimately become the inflatable ring 13, importantly
includes a rugged core element 20 which can be accurately
' and unyieldingly secured to the outer elements of the mould.
In Fig. 4, such outer elements are shown to comprise: a base
' 21 to which core 20 can be secured as by bolt means 22; right
and left separable parts 23, 24, which will be understood
to
be clampable to each other and to plate 21 (by means not
WO 94/17848 ~ ~ ~ ~ PCT/GB93/00578
8
shown) but to be accurately located as by dowel pins 25; and
a threaded removable pin 26 which enters a local bore 27 in
core 20, in order to integrally form the air-supply feature
17.
A peripherally continuous space 28 between core 20 and
the cooperating outer mould parts 20, 21, 23 , 24 will be seen
to account for the moulded intermediate product of Fig, 2.
Briefly, this intermediate product comprises a thin-walled
skirt 30, depending from an essentially flat but thicker
annulus or flange 31, to the upper inner edge of which a
thin-walled shallow dome (flexible membrane 18) effectively
closes the lumen within annulus 31, all except for the plural
apertures which define longitudinal bars or strips 19 near
the proximal end of dome 32. The skirt 30 is characterized
by a peripherally continuous lower rim 33 of essentially the
same peripheral extent as the outer edge of~ annulus 3~1.
Between annulus 31 and the lower rim 33, the moulded skirt
30 features a peripherally continuous radially outward convex
bulge 34 which becomes concave near its juncture with annulus
31 and near the lower rim 33; in the case of the upper
concave portion 35, juncture with annulus 31 is virtually
normal to the plane of annulus 31, and in the case of the
lower concave portion 36, termination at rim 33 is virtually
normal to the geometric lower plane defined by rim 33.
Preferably, the moulded longitudinal or major-axis span S~ of
the lower end of skirt 30 is substantially equal to or less
than the corresponding span S2 between major-axis limits of
the upper surface of annulus 31.
As shown, a radially short outward flange formation 37
is a feature of rim 33, resulting from a local mould-cavity
feature 37' in the mould of Fig. 4, the same being adjacent
to and defined in part by the flat upper surface of the mould
base 21. Correspondingly, the radially outer, upper edge of '
annulus 31 is notched to define a ledge 38 into which flange
formation 37 can fit when skirt 30 is flexibly inverted or
WO 94/17848 PCT/GB93100578
9
reversed so as to convert the convex bulge 34 into an outer
concavz contour which is smoothly contiguous to the concave
portions 35 and 36, thereby resulting in virtual completion
of the inflatable ring 13 of the mask of Fig. 1. In the
process of inversion of skirt 30, what had been an inwardly
directed feature 17' of the moulded skirt 30 (Fig. 2) also
was reversed to project outwardly and thereby to define the
inflation/deflation air-connection feature 17 of inflatable
ring 13. The above-stated preferred S~/S2 relationship will
be seen as assuring a natural fit of flange 37 to notch 38,
upon inversion of skirt 30.
In the matter of membrane 18 and its apertures with
integrally formed bars or strips 19 therebetween, it will
be noted that the moulded apertures are shown in Fig. 4 to
result from local rounded or ridge-like projecting
formations, as at 29 in core 20. Projections 29 will be
understood to feature outer-surface convex contouring that
conforms precisely to concave contouring of the outer-mould
cavity, to and against which projections 29 fit and abut,
upon proper mould closure. Thus, at projections 29, mould-
core (20) structure offers stabilizing reference to outer-
mould structure (e. g., 23) for assurance of uniformly thin
development of the moulded skirt 30 which must ultimately
be
reversed to define inflatable ring 13.
Thus far, mould formations of Fig. 4 have been described
only to the extent necessary to form the cavity which will
define the intermediate or skirted product of Fig. 2.
Various mould designers will have preferences for spree
accommodation, but in Fig. 4, the phantom spree-passage
designation 39 will be understood to suggest an advantage
in
A
having the flange-forming cavity 31' serve as an excellent
manifold for efficient distribution of the silicon-rubber
or
the like material that is injected under pressure in the
moulding process. Moreover, when the moulded intermediate
product of Fig. 2 is cured sufficiently for removal from the
WO 94/17848 ~ ~ ~ PCT/GB93/00578
mould, the sprue material will readily part company from the
thick wall of flange 31, and if such parting leaves a slight
r
upwardly projecting fragment, such fragment will be exposed
to view for visual spotting and ready removal, suitably after
5 mould parts 23, 24, 26 have been removed and while the
intermediate product of Fig. 2 remains unstripped from core
20. A burr-equipped portable drill is a satisfactory tool
for cleaning off any remnant sprue projection, and also for
cleaning off any flashing or the like that may be observed
10 at openings of membrane 18.
Having inspected and, if necessary, cleaned up the
moulded intermediate product, it is now ready for stripping
from the core 20. Since the bottom edge or rim is reinforced
by flange formation 37 and is nevertheless flexible and
stretchable, the stripping operation involves no sore than
a local upward peeling of the skirt rim from core 20. Once
locally past the bulge 34' of the core, the moulded product
is quickly and safely removed and is ready for the simple
step of inversion, placing flange 37 into engagement or
near-engagement at the peripheral notch 38 of flange 31.
Preferably, the engageable surfaces of flanges 37 and 31 will
have been first coated with suitable silicone adhesive, in
readiness for adhesive completion of ring 13 upon reversal
of the skirt 30, as above described. The thus-reversed
intermediate product of Fog. 2 will then have the appearance
depicted in Fig. 3, as seen from the laryngeal-inlet side.
The mask of Fig. 1 is then completed by assembling the
separately moulded plate component 12 (Fig. 2A) thereto.
This component 12 is seen to be of thicker wall structure
than skirt 30 and is therefore less compliant, although it
may be moulded from the same silicone-rubber material as is
the intermediate product of Fig. 2. Its bottom surface 16
is a flat generally elliptical annulus, conforming to the '
profile of the flat upper surface of flange 31 and extending
slightly beyond so as to additionally lap.the flat underside
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11
of skirt flange 37, after skirt 30 reversal and assembly to
notch 38. Again, the bottom surface 16 of plate 12 and the
upper exposed surface of flange 31 (with flange 37 in
assembled position) will be understood to have been precoated
with suitable adhesive, so as to retain the parts of Figs.
2 and 2A, once they are assembled. The plate 12 of Fig. 2A
will then offer its cylindrical counterbore 40 for assembling
connection to the airway tube 11, and the inflation formation
17 of the inflatable ring 13 will be ready to accept assembly
of the~flexible inflation/deflation supply tubing 41 shown
in Fig. 1. The mask article of Fig. 1 may then be deemed
to be complete, but it is my preference to lay down a bead-
of silicone adhesive in the peripherally continuous groove
42 established by the adjacency of (a) the outer exposed
generally elliptical limiting contour of plate 12 and (b) the.
now-inverted but previously lower rim of skirt 30. The'
designation 42 in Fig. 1 will be understood to designate such
a bead, which becomes a fillet between adjacent exposed
surfaces of plate 12 and ring 13; as described more fully in
my copending U.S. Patent No.5,297,547,filed
July 30, 1992, such a fillet aids in the desired collapse of
ring 13 when evacuated for ease of insertion of the mask of
Fig. 1 into and removal of the same from a patient.
Figs. 4A and 4B illustrate a simplified technique for
manufacture of the described intermediate product, using
essentially only the core piece 20 of Fig. 4. In Fig. 4A,
the core piece 20' will be recognized as being identical to
core piece 20, with the single exception that a threaded plug
44 has been engaged to a tapped hole at the base end of the
bore 27 which will ultimately define the inflation/ deflation .
connection 17. The point of Fig. 4A is that the depicted
'core piece 20' lends itself to so-called dip-moulding,
namely, by manipulating core 20' via its base-mounting 21'
such that it is inverted and dipped into a pool of liquid
moulding material of appropriate viscosity. Dip repetition
WO 94/I7848 ~ ~ ~ PCT/GB93/00578
12
and total exposure to the liquid moulding material enables
wall thickness to build to desired extent, resulting in an
intermediate skirted product 45 (Fig. 4B) which closely
resembles the product of Fig. 2; the dipped product can be
stripped from core 20' after sufficient cure and after
unthreading plug 44 from core 20'. The stripped product has
the features of Fig. 2 except that there is no flange (37)
at the bottom end of skirt 30', and there is no associated
notch (38) at the outer periphery of what is now a
thin-walled flange 31' against which the conforming flat
bottom edge 16 of plate 12 is to be fitted and adhesively
retained. The relation of the outer contour of plate 12 to
the outer contour of flange 31' is such that a flat outer rim
portion 46 remains exposed for adhesively retained reception
of the bottom edge 33' of skirt 30', once the skirt 30' has
been reversed so as to complete the envelope of an inflatable
ring 13' . A filler bead 47 of silicone adhesive is laid down
into the exposed groove defined by adjacent surfaces of ring
13' and plate 12, to complete the thus-assembled laryngeal
mask, with almost as many of the features as apply to the
mask produced from parts and procedures described for Figs.
1 to 4, but at a mere fraction of the cost for mould parts
and pressurizing equipment needed for the procedure of Figs.
1 to 4.
In the embodiment of Fig. 5, the back-plate formation
50 is integrally moulded to and as part of the same process
as that in which the skirt (Fig. 6) and its
inflation/deflation connector 17 are formed, prior to
inversion to establish a peripherally continuous inflatable
ring 51. The completed laryngeal mask (Fig. 5) is
functionally the equivalent of the mask of Fig. 1 and is w
shown connected in the same way to airway tube 11 and to the
supply tubing 41 for inflation/deflation of the inflatable
ring 51.
WO 94/17848 PCT/GB93100578
13
More specifically, the mould of Fig. 7, which enables
one-step moulding of the entire mask of Fig. 5, is seen to
comprise a core 52 having a large area base that is securely
referenced to a flat outer-mould base 53 and retained~as by
bolt means 54. The outer components of the mould are
simplified to show establishment of a single cavity in
outer-mould structure 55, supplied as by injection of liquid
moulding material via one or more sprue passages, suggested
at 56.
The back-plate portion 50 of the intermediate moulded
product of Fig. 6 is seen to be of greater thickness than the
uniformly thin flexible wall of the skirt formation 57 which
integrally depends from the geometrical plane of juncture
with back-plate 50: in Figs. 6 and 7 this geometrical plane
is identified 58-58. Features of skirt formation 57 may be
identical to those of skirt 30 in Fig. 2. Therefore, the
same reference numerals have been repeated for skirt 57 in
Fig. 6 and for mould-cavity skirt-forming features in Fig.
7.
Above the plane 58-58, the mould-cavity profile 59 is
seen to account for essentially the same back-plate external
profile at 50 as for the separately moulded part of Fig. 2A.
However, at juncture with the flange-like annulus 60 at the
base of back-plate formation 50, a peripherally continuous
shallow groove 61 is formed by a short inward flange feature
61', sized to provide for located reception of the lower
flange 37 of the skirt 57, when inverted. Within the mould
cavity and above the plane 58-58, the core 52 rises with a
convergent upper body portion which is profiled to establish
internal features of the back-plate 50. Specifically, an
acute-angle truncation which is at acute inclination to the
plane 58-58 and to the axis 62 of airway-tube reception is
provided with ridge formations 63 analogous to those at 29
in Fig. 4, to establish the spaced apertures in a membrane
64 for a ventilating flow through the completed mask. In the
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14
case of Fig. 7, however, the outer surfaces of formations 63
are flat and in the said plane of truncation, for clean fit
to the flat truncated distal end 68' of a mould-cavity
defining plug 68 which is retractably guided in a bore of
outer-mould structure 55, and which has a shoulder 65' to '
define a limit stop at 65 in the airway-tube reception bore -
of plate formation 50.~
- It will be understood that flexed inversion of skirt 57
of the intermediate moulded product of Fig. 6 will bring
lower -flange 37 into engagement with groove 61, for
adhesively retained completion of the toroidal inflation ring
51. Also, it will be noted that the fitted adjacent surfaces
of plate 50 and of the inverted skirt 57, near the lower end
of the inverted skirt, will accept the recommended provision
of a silicone fillet, suggested at 67 in Fig. 5.
The embodiment of Fig. 8 and its manufacture are
generally as described for the embodiment of Fig. 5, except
for the additional provision for oesophagus drainage pursuant
to the disclosure of pending U.S. patent No.5, 241, 956,
filed July 24, 1992. Parts in Fig. 8 and in related
Figs. 9 and 10 which correspond to those of Figs. 5, 6 and
7 are given the same reference numbers, so that description
is thereby simplified. The additional function of oesophagus
drainage in Fig. 8 is provided by a re-entrant flexible
drainage-tube formation 70, integrally formed with skirt 71
in the single moulding operation which creates the
intermediate product of Fig. 9, and which upon skirt
reversal, positions the drainage-tube formation 70 upon the
upper surface of the back-plate 50' and poised for assembly
of flexilale tubing 72 thereto, for external evacuation of
discharges) from the oesophagus.
To accomplish the integrally moulded creation of the
drainage-tube formation 70, the outer mould component 55' is
shown to have a cylindrical bore 73, for removably connected
accommodation of a plug element 74 which is coaxially spaced
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within bore 73 by reason of threaded mounting near the outer
wall surface of outer-mould structure 55'. When in readiness
for a moulding operation, the unthreaded end of plug element
' 74 is either in contact with the most distal bulge forming
5 region 34' of the skirt cavity 28, or, as shown, is fitted
into'a local bore of core 52, so that core contouring around
the~open end of the bore can develop a smoothly rounded
internal contour 69 (Fig. 9j; in Fig. 8, the contour 69 of
Fig. 9 is seen to account for the smoothly rounded inlet of
- 10 the evacuation passage to tube 72. ~ .
- - A shallow groove formation 75 (see Fig: 9j at the distal
end of the outer profile of back-plate formation 50' is- sized
for nested accommodation of the evacuation tube 72, when
assembled to tubular formation 70. And a local arcuate
15 cut-out" 76, defined by a local outer-mould formation 76',
enables the skirt 71' , upon inversion, to f it over and around
tubular formation 70, thus simplifying the process of
securing and sealing the inflatable ring 71 which is produced
by inversion of skirt 7I'. Having thus completed the
assembly of the mask of Fig. 8, it is recommended, as
previously, to establish a fillet of silicone adhesive for
the full peripheral continuity of lower skirt adjacency (when
inverted] to the base profile of back-plate 50', this fillet
should extend for full sealing effectiveness around formation
70 at cut-out 76, for inflation/deflation operability of ring
71. At the same time, it is recommended the same adhesive
be applied in one or both of the grooves defined by
evacuation tube 72 and by the adjacent upper longitudinal
profile of back-plate 50', thereby adding a measure of
back-plate reinforcement to the adhesively completed assembly
of the mask of Fig. 8.
In an alternative situation in which an inflatable
cushion is an added feature on the exposed backside of plate
50' and the adjacent inflatable ring (71j surface, in
accordance with teachings of my copending U.S. Patent
CA 02155112 2003-O1-27
696'75-597
16
No.5,241,956. filed September 28, 1992, the inflatable
cushion need merely cover the unsealed location of "cut-out"
76 around tubular formation 70, whereby to enable inflation
of ring 71 to concurrently. inflate the cushion, and deflation
of ring 71 to concurrently deflate the cushion: however, for '
more reliable concurrent inflation of ring 71 and the
cushion, it is preferred to drill an aperture 78 in the skirt
of Fig. 9 near but offset above flange 3?, for assured air
communication between ring 71 and the cushion. As explained
' 10 in said U.B. Patent No.5,241,956, the inflated condition
of the cushion, which may have a potentially inflated contour
suggested by phantom line 77, enables the cushion to bear
against the back wall of the pharynx for gently loaded
application of inflatable ring 71 into its intended sealing
engagement with the laryngeal inlet. More specifically, the.
cushion schematically indicated in Fig. 8 comprises a
suitably cut shell of thin flexible material adhered
peripherally to the equator (suggested at 79) of the
inflatable ring 71 and suitably apertured to fit around and
be adhesively sealed to the two tubular members 50' and 72.
The described embodiments of the invention will be seen
to meet stated objects, significantly reducing the complexity
and cost to manufacture each of a variety of laryngeal-mask
configurations. In addition to the advantage of being able
to produce the inflatable ring with uniformly controlled
material thickness, there is a further advantage which may
not be immediately apparent; this further advantage results
from cooperating factors which follow from (a) producing the
inflatable ring with uniform or precision-controlled
3o thickness, and (b) inverting.the pre-moulded skixt to create
the ring in a naturally toroidal envelope wherein inner and
outer circumferential surfaces of the envelope are in lightly
but uniformly stressed opposition, so that circumferential
compressional stress at the inner surface of the envelope is
in equilibrium with circumferential hoop-tension stress at
~VO 94/17848 ~ PCTIGB93/00578
17
the outer surface of the envelope. The fact that wall
thickness is circumferentially uniform accounts for natural
circumferential uniformity in the ring section. The fact
that this uniform thickness can be reliably made thinner than
S the "nominal" greater thickness of prior constructions is
responsible (a) for greater flexible collapse of the mask to
a smaller, more pliable structure when evacuated (for
insertion in or removal from a patient) , and (b) for more
compliantly adapted conformability with abutting. profile
features of the laryngeal inlet when inflated in installed
position. ,
More specifically with respect to the indicated
equilibrium between opposed compressional and hoop-tension
stresses, it will be understood that, upon completion of any
of the intermediate products of Figs . 2 , 4B, 6 and 9 , the
involved thin flexible skirts are in relatively unstressed
condition while still in the shape to which they were
moulded. Inverting the skirt brings the lower edge of the
skirt into adjacency (if not into circumferentially
continuous engagement) with the moulded upper edge of the
skirt, so that what was the outer surface of the skirt is
thereafter the inner surface of the inflatable ring; at the
same time, what had been the inner surface of the skirt is
thereafter the outer surface of the inflatable ring. However
thin the moulded thickness of the skirt, it necessarily
follows that the moulded inner surface of the skirt is of
less circumferential extent than the circumferential extent
of the moulded outer surface. But on skirt inversion, what
was an inner surface of unstressed lesser circumferential
extent becomes an outer surface of necessarily greater, but
tension-stressed, circumferential extent; at the same time,
on skirt inversion, what had been an outer surface of
unstressed greater circumferential extent becomes an inner
surface of necessarily lesser, but compression-stressed,
circumferential extent. It is these two opposing stresses,
WO 94/17848 PCT/GB93/00578
18
attributable to forced opposing changes in peripheral extent,
that account for the indicated equilibrium, regardless of
moulded skirt thickness, even for presently preferred
relatively thin skirt-thickness dimensions in the range 0.4
to 1.0 mm, it being noted that laryngeal masks must be made
in a range of sizes, including a range of inflatable-ring
thickness, for best accommodation to laryngeal-inlet
dimensions of the patient, whatever his age and stage of
physical development. Within the stated range of
inflatable-ring thickness, it is presently preferred to mould
the skirt to a thickness of substantially 0.7 mm, a dimension
which is recommended for most laryngeal masks of
adult-patient sizes.
