U.S. patent number 3,734,100 [Application Number 05/128,898] was granted by the patent office on 1973-05-22 for catheter tubes.
This patent grant is currently assigned to E. T. Manufacturing Co., MPC/Kurgisil, a joint venture of Medical Products Corp.. Invention is credited to Seymour Bazell, Edward M. Goldberg, Ralph G. Ostensen, Robert D. Walker.
United States Patent |
3,734,100 |
Walker , et al. |
May 22, 1973 |
CATHETER TUBES
Abstract
Improved catheter tubes and their method of construction having
a comformable balloon cuff of silicone rubber of low hardness,
modulus, and stress values, and which results in less pressure
necrosis and cuff failure in use. Specific examples include
endotracheal tubes, Foley catheters, tracheostomy tubes, urethral
catheters, and catheters for use in gastric, esophageal,
pharyngeal, nasal, intestinal, rectalcolonic, choledochal, arterial
venous, cardiac and endobronchial applications.
Inventors: |
Walker; Robert D. (Racine,
WI), Bazell; Seymour (Skokie, IL), Goldberg; Edward
M. (Glencoe, IL), Ostensen; Ralph G. (Morton Grove,
IL) |
Assignee: |
MPC/Kurgisil, a joint venture of
Medical Products Corp. (Skokie, IL)
E. T. Manufacturing Co. (Skokie, IL)
|
Family
ID: |
10167633 |
Appl.
No.: |
05/128,898 |
Filed: |
March 29, 1971 |
Current U.S.
Class: |
128/207.15;
604/103 |
Current CPC
Class: |
A61M
25/1034 (20130101); A61M 25/1029 (20130101); A61M
16/0486 (20140204); A61M 16/0445 (20140204); A61M
16/0484 (20140204); A61M 16/0443 (20140204); A61M
16/04 (20130101) |
Current International
Class: |
A61M
16/04 (20060101); A61M 25/00 (20060101); A61m
025/00 (); A61m 016/00 () |
Field of
Search: |
;128/348,349B,35R,351,325,344,246 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Cooper et al. Surg, Gyne. & Obstet. December 1969 Vol. 129 pp.
1235-1241.
|
Primary Examiner: Truluck; Dalton L.
Claims
We claim:
1. An improved catheter comprising:
a. a tubular, silicone rubber body portion having an outer surface
and a central passage therein extending axially in said body from a
proximal to a distal end, said distal end being shaped to provide a
smooth, gently pointed tip for ease of insertion into contact with
tissues, and said central passage communicating with an opening at
the distal end thereof,
b. an axially extending inflation lumen disposed contiguous with a
wall of said body portion defined between said outer surface
thereof and said central passage therein,
said inflation lumen communicating with a pilot tube disposed
adjacent the proximal end of said body portion,
c. an expansible cuff portion disposed medially of said distal end
of said body portion and communicating with said inflation
lumen,
said expansible cuff portion being substantially cylindrical in its
initial deflated condition and having proximal and distal margins
circumferentially secured to said body portion, and conforming
generally to the outer surface shape of said silicone rubber body
portion in its initial deflated condition,
said expansible cuff portion being composed of a low modulus
silicone rubber having properties of a Shore A hardness of less
than about 30, a tensile strength of below about 700 psi, an
elongation of above about 1,000 percent, and a stress value upon
sealing inflation of less than about 30 percent of the breaking
stress of said cuff material, said properties of the silicone
rubber cuff thereby resulting in pressures, at substantially
complete seal, of less than vascular compressive pressures inducive
of significant tissue pressure necrosis,
whereby said cuff upon expansion conforms to irregularities in
contacted tissue surfaces and provides lateral sealing while
reducing lesions.
2. An improved catheter as in claim 1 wherein the wall thickness of
said cuff is preselected to provide for a predetermined, controlled
shape of the cuff when inflated.
3. An improved catheter as in claim 2 wherein said cuff walls are
preselected to vary in thickness in cross-section.
4. As improved catheter as in claim 2 wherein said cuff walls are
preselected to vary in thickness in an axial direction.
5. An improved catheter as in claim 1 wherein the cross-sectional
shape of said body portion is preselected to substantially conform
to a body cavity in which said catheter is used.
6. An improved catheter as in claim 5 wherein the wall thickness of
said cuff is preselected to provide for a predetermined, controlled
shape of the cuff when inflated.
7. An improved catheter as in claim 1 having a plurality of
inflation lumens disposed in said body portion walls.
8. An improved catheter as in claim 1 wherein said distal end is
adapted for use as an endotracheal tube.
9. An improved catheter as in claim 1 wherein said distal end is
adapted for use as a Foley-type catheter.
10. An improved catheter as in claim 1 wherein said Shore A
hardness is less than about 25, said tensile strength is in the
range of from about 500-600 psi, said elongation is in the range of
from about 1,000 to 1,500 percent, and said stress value upon
sealing inflation is in the range of from about 15-25 percent.
11. An improved catheter as in claim 1 wherein said main body is a
silicon rubber of hardness greater than said cuff.
Description
This invention is directed to improved cuffs for catheters, for
example, endotracheal tubes, and to a method of construction of the
improved catheters. More particularly, the invention is directed to
a special molded silicone rubber conformable cuff having low values
of hardness, modulus and stress, the latter expressed as a
percentage of the breaking stress of the cuff.
BACKGROUND
Catheters are extremely important and useful medical tools for the
input or withdrawal of fluids from the body of a patient.
Generically, catheters are tubular in shape and have a retaining
and/or sealing inflatable balloon cuff near the distal (intra
corporeal) end of the tube. Often the catheters must remain in
place for substantial periods of time. Present catheters have not
been entirely satisfactory since they tend to cause tissue necrosis
from pressure or biochemical incompatibility of the inflatable
balloon cuffs. For example, standard rubber cuffs of endotracheal
tubes in place for as little as 72 hours can cause severe pressure
necrosis. Latex material is chemically irritating and
polyvinylchloride plastic cannot elongate sufficiently to provide
adequate balloon volumes, has no memory and prunes upon deflation.
A more detailed discussion of the serious aspects of these problems
follows, with special emphasis on endotracheal tubes, by way of
example.
In cases of patients requiring general inhalation anesthesia, the
quickest and easiest way to insure a clear upper airway for
ventilation of the lungs is by endotracheal intubation. In the
simplest of terms, this involves slipping a tube down to the
trachea through the larynx to provide an air passage to the lungs.
The patient's head is supported and the neck is slightly flexed on
the trunk to provide for a relatively straight-line approach to the
larynx. The jaw is kept apart, and the tube is slipped directly
down into the trachea. This process can be accomplished in a very
few seconds, which in an emergency may be life-saving since the
person who cannot breathe adequately will be dead within minutes.
This also eliminates obstruction of the breathing passage by vocal
cord spasms since the tube is directed through the larynx.
While uncuffed tubes have been used, they do not seal off the
trachea from the digestive tract and aspirate. Further, they do not
provide a closed system and positive pressure ventilation.
Endotracheal tubes having an expansible cuff which effectively
seals off the trachea, retains the tube in place, and provides a
passage therethrough, have been used for some time. Once in place,
a cuff-type endotracheal tube provides the following advantages. A
clear upper airway is insured. Aspiration of blood, mucus and
vomitus into the lungs is prevented. Resistance to air flow and
thus the oxygen consuming work of breathing is reduced. An Ambu bag
or a positive-pressure respirator may be employed to assist
ventilation. The excessive secretions causing lower airway
obstruction can be easily removed by direct aspiration. Inhalation
anesthesia can also be given easily, if required. Use of the cuff
provides a closed system such that oxygen or other gases can be
given in a controlled and measured manner and that carbon dioxide
can be removed under controlled circumstances.
Recent reports have clearly established the relationship between
the use of cuffed endotracheal tubes and subsequent occurrence of
various types of tracheal injury, including tracheal stenosis,
tracheal malacia, or tracheo-esophageal fistula at the cuff site.
Tracheal stenosis is the more frequent of these complications, and
has been estimated to occur in up to 15 percent of the patients
whose survive prolonged ventilatory assistance by means of the
tubes. The tracheal injury is due to pathologic evolution of
necrosis as a result of the pressure at the site of contact between
the balloon cuff and the tracheal wall. Present expansible cuffs or
balloons require sufficiently high pressure that the tender mucosal
membrane is severely injured by prolonged contact therewith.
Several techniques have been developed in clinical practice to
reduce the hazard of the tracheal injury. These include careful
inflation of the cuff with a volume of air just sufficient to
provide a seal with the tracheal wall. However, since the tubes are
frequently subjected to forces of mechanical aspirating equipment,
movement of the patient and the like, the amount of pressure must
be sufficient so that the seal between the outer balloon wall and
the trachea is sufficiently secured to resist such forces. This
unfortunately results in necrosis-causing cuff pressures. The
second technique involves hourly deflation of the cuff for 5
minutes, and a third method involves alternating the site of
contact with the tracheal wall by use of double-cuffed tubes which
are periodically and alternately inflated and deflated.
Recent studies of Bryant et al. (Journal of American Medical
Association, Volume 215, No. 4, pages 625-628, "Reappraisal of
Tracheal Injury from Cuffed Tracheostomy Tubes") indicates that
such widely practiced techniques of hourly deflation of the balloon
cuffs fail to protect the trachea from significant injury. In
addition, the contour deformity or out-of-roundness of the trachea,
low compliance and high intra-cuff pressures characteristic of
presently used balloons and accidental over-inflation of the cuffs
are the principal causes of tracheal injury.
The method of alternating cuff sites also fails to prevent
significant injury. Indeed, because the cuffs extend over a greater
length of the tube, the injury is also more extensive and makes the
operative repair of tracheal stenosis or tracheal-esophageal
fistula more difficult. The above authors devised a "minimal" leak
technique, in which the balloons were first inflated to a no-leak
position and then a sufficient amount of inflation air was
withdrawn until an audible leak occurred with each inspiration.
While this reduced the hazard of excessive cuff inflation, it does
not prevent rotation, slipping or leakage of the tube, and may also
permit a certain amount of aspiration of fluids into the lungs.
Still another approach to stenosis problems was reported by Arens
et al. in the Journal of Thoracic and Cardiovascular Surgery,
Volume 58, No. 6, December 1969, "Volume-Limited Intermittent Cuff
Inflation for Long-Term Respiratory Assistance." This involves the
use of endotracheal intubation with polyvinyl-cuffed endotracheal
tubes using Bird respirators. The cuff is inflated periodically,
timed to be inflated to a volume at which the cuffs would not leak
at the peak of inspiration. This provides a preset volume-limited
intermittent cuff inflator for use in both pressure-limited and
volume-limited ventilation. The clinical and experimental evidence
reveals that such intermittently inflated cuffs produce less
tracheal damage than does a cuff that is constantly inflated. While
there were no evidences of severe errosion of the trachea or
dilation, a majority of the subjects had up to moderate
effects.
The practice of alternating two cuffs at different levels results
in a larger area of stenosis because the width of each cuff is
relatively narrow. High pressures are required to inflate a narrow
cuff, and thus the lateral pressure on the tracheal mucosa is also
greater. If the lateral pressure due to cuffs approximates or is
greater than the capillary blood pressure in tissues, ischemia may
readily be produced, especially when a patient is in hypotensive
shock. Ischemic damage results in weakness of the tracheal wall,
dilation, fibrosis, and finally, tracheal stenosis.
Still another suggestion to the problems of trauma connected with
pressure necrosis due to the cuff has been that of Drs. Kamen and
Wilkinson. Their measurements show that with standard cuffed
endotracheal tubes presently in use, for example, a No. 34 red
rubber endotracheal tube show intra-cuff levels of 280 mm. Hg and
at the tracheal wall, that is between the cuff and the trachea, as
high as 200 mm. Hg. Kamen and Wilkinson devised a latex cuff in
which the intra-cuff space was filled with a polyurethane foam.
This cuff operates in a manner the reverse of the usual cuff, that
is, the cuff is always in the extended shape with the latex sheath
stretched over the ball of polyurethane foam through which the tube
extends. In order to insert the Kamen tube, the pilot tube is
attached to a vacuum, and the low pressure draws out some of the
air in the polyurethane foam cells. The pilot tube is then pinched
shut and the cuff in the relatively deflated form is then inserted
through the larynx into the trachea.
However, the Kamen construction has two very serious drawbacks.
First, the deflated size of the cuff is substantially larger than
the tube itself in view of the fact that the nature of the
polyurethane foam prevents all of the cells from being open. Thus,
it cannot be entirely evacuated, and the deflated volume is
physically larger than the standard latex or polyvinylchloride
empty balloon. Secondly, the endotracheal tube can become trapped
in the patient and impossible to remove other than by surgical
procedures when the external pilot tube becomes blocked, clogged,
cut or separated from the latex sheath. In short, the polyurethane
foam acts as a physical spring exerting an outward pressure against
the latex sheath, and the spring must be collapsed by the vacuum.
In addition, the ability to collapse the polyurethane foam depends
upon the integrity of the latex sheath. Where the integrity is
disrupted or broken, it will be impossible to pull sufficient
vacuum through the pilot tube to collapse the polyurethane foam to
a diameter small enough to be able to remove the endotracheal tube
through the larynx. Likewise, in field emergency situations, where
no vacuum creating source is available, such tubes cannot be used.
In contrast, the cuffs of our tubes can be breath inflated if
necessary. While the Kamen polyurethane foam filled sheath type of
cuff does have the advantage of relatively low pressure exerted
between the cuff and the tracheal wall, the danger of impossibility
of removal is a serious drawback. From the point of view of safety,
it is far better if a rupture of the cuff causes deflation and a
loss of securing pressure, rather than leading to impossibility of
removal.
Another type of cuffed catheter is a Foley type urethral retention
catheter. This urethral retention catheter is utilized for
prolonged or chronic bladder drainage. The catheter is retained
within the bladder by inflating the cuff. This prohibits it from
being withdrawn through the urethra. The inflated cuff may cause
undesirable pressure against the bladder wall or urethra. These
problems are further complicated in cases involving an enlarged
prostrate. As in the endotracheal tube, the cuff pressures and
conformability are significant.
A recent attempt to adapt silicone rubber to use in Foley-type
catheters, U.S. Pat. No. 3,547,126, follows the prior art of having
a balloon substantially round in cross section of a relatively hard
silicone rubber. The inflation pressures, and predictably the
pressure necrosis, is not appreciably different from the standard
rubber latex, or polyvinylchloride cuffs. In addition, the
non-conformable round balloon shape provides only for point contact
(in cross section) with the interior of the bladder.
Finally, the wall thickness of latex, rubber or silicone cuffs
constructed by the common dip coating process is, practically
speaking, impossible of reproducible, controlled thickness.
Manufacturing rejects and unexpected "bulge" failures are
relatively high.
THE INVENTION
Objects
It is among the objects of this invention to provide improved
cuffed catheter tubes such as endotracheal tubes, Foley-type
urethral retention catheters, urethral catheters, and catheters for
use in gastric, esophageal, pharyngeal, nasal, intestinal,
rectal-colonic, choledochal, arterial, venous, cardiac,
endobronchial and tracheostomy applications, which have a
low-pressure conformable cuff of physio-logically compatible
material.
It is another object of this invention to provide a catheter having
a special conformable cuff therefor, which overcomes the
difficulties described above with respect to the prior art.
It is another object of this invention to provide improved
catheters, for example, endotracheal tubes which are simple of
construction and operation, and which provide for secure retention
and sealing against movement, aspiration or fluids leakage, yet
which provide a seal of sufficiently low pressure that tissue
damage due to pressure necrosis is reduced.
It is another object of this invention to provide a conformable
cuff for catheters generically, which cuff is a physiologically
acceptable silicone rubber composition, and which has special
properties of low values of hardness, modulus and stress, the
latter based on a percentage of the breaking stress, and yet which
is tear resistant, extremely soft, easily distensible, and will
conform to irregularities in the passage or body cavity in which it
is placed.
These and other objects of this invention will become evident from
the detailed description which follows.
THE FIGURES
The detailed description has reference to the following FIGS.:
FIG. 1 is a perspective view of one type of catheter, specifically
an endotracheal tube, in accord with the invention.
FIG. 2 is a longitudinal sectional view along the line 2--2 in FIG.
1, showing the cuff in a substantially deflated position.
FIG. 3 is a cross-sectional view along the line 3--3 of FIG. 2.
FIG. 4 is a longitudinal sectional view of the cuff area of the
catheter showing it in partially inflated position.
FIG. 5 shows the method of insertion of an endotracheal tube in the
trachea of a patient.
FIG. 6 shows one method of inflation of the cuff of the tube in
position.
FIG. 7 shows in cross-section another embodiment of the invention
where the main tube and cuff walls are of predetermined varying
thickness to provide controlled balloon inflation, shape and
size.
FIG. 8 shows partly in section the principles of this invention
adapted to a Foley-type catheter in the inflated condition in use
in the urinary bladder.
FIG. 9 shows, partly in longitudinal section, cuff walls that vary
longitudinally in thickness to provide for differential expansion
such as shown in FIG. 8.
SUMMARY
We have discovered that catheters having conformable cuffs made of
a silicone rubber having preselected low values of hardness,
modulus, and stress, the latter expressed as a percentage of the
breaking stress and which is extremely soft, provide a cuff that is
tear resistant, easily distensible, and will permit complete
sealing, even over irregularities, with reduced pressure necrosis.
We have also found that the basic theory of pressure cuffs of the
prior art appears to have been in error. The prior art cuffs
specify a balloon material which has a relatively high tensile
strength, on the assumption that this will prevent rupture of the
balloon cuff under the stress which it encounters in use. In
addition, the balloon material has been chosen to have a relatively
high hardness and low percentage elongation to provide for
sufficient lifetime and mechanical strength against rupture.
However, these properties lead to relatively high intra-cuff
pressures, a generally spherical balloon shape which is axially
centered around the main catheter tube, and requires a relatively
high inflation pressure. As a result, the pressure on the tissues
contacted by the cuff upon inflation is sufficiently high to cause
tissue necrosis.
In contrast, we use an extremely soft, silicone rubber which has a
relatively low tensile strength and high elongation. We have
discovered that the cuff material should have a definite strain
rather than stress value and should be able to assume the given
strain value at the lowest possible stress value. The stress value
should represent as low a percentage of the breaking stress as
possible. In addition, the low value of stress, based on the
percentage of the breaking stress, and the softer silicone rubber
composition permits the cuff to more completely conform to
irregularities of the passage or body cavity, e.g., a trachea,
without developing high areas of stress. The conformability allows
more equal pressure distribution when the cuff is subjected to
pressure variations. This eliminates high point pressure loadings
on the tissue. Any type of physiologically compatible plastic or
rubber material which meets these criteria may be used. We prefer
to use a silicone rubber which meets the above critical parameters.
Not only does this rubber have accepted physiological
compatability, but it may be compounded and cured to the required
degree of softness, low hardness, relatively low tensile strength,
and high percentage elongation of breaking stress.
DETAILED DESCRIPTION
Referring now to the Figures, the following detailed description is
made with reference to a specific embodiments of an endotracheal
tube and a Foley-type catheter. However, these embodiments are
merely illustrative and not limiting of the principles of the
invention which may equally be applied to catheters for use in
endotracheal tubes, Foley catheters and catheters for use in
gastric, esophageal, pharyngeal, nasal, intestinal, rectal-colonic,
choledochal, arterial, venous, cardiac, endobronchial and
tracheostomy applications.
FIG. 1 shows a general perspective view of one embodiment of an
endotracheal tube illustrating the principles of this invention. At
the proximal end of the tube 1 (in the right of FIG. 1) is a pilot
tube 2 which connects with a cuff inflation lumen 3 in the wall 4
of the main body 34 of the endotracheal tube. The lumen continues
along the length of the tube to an opening 5 beneath the cuff 6.
The proximal end also has an adapter means 7 for connection with
mechanical or hand aspiration means. The adapter 7 may or may not
be used depending upon the medical condition of the patient. The
adapter communicates with a central passageway 8, which is a
ventilation passageway in the case of an endotracheal tube, and a
drainage passageway in the case of a Foley-type catheter (see
passage 9 in FIGS. 8 and 9). The tube 1 is preferably made of a
silicone rubber which is smooth throughout its entire length. Such
tube may be made by an extrusion process in which the lumen 3 is
extruded simultaneously with the central passageway 8. The lumen 3
extends distally along the main body under the cuff 6 so that the
lumen communicates with opening 5 and the intra-cuff space 11. It
is an important aspect of this invention that the cuff silicone
rubber material be relatively soft compared to the silicone rubber
material used for the tip and shaft. The latter must be relatively
hard to facilitate insertion while the cuff silicone rubber
material must be relatively soft to provide conformability.
The distal tip 12 of the tube 1 may be bias or diagonal cut as at
13 and chamfered as at 14 so as to prevent tissue trauma upon
insertion. In addition, the diagonal cut 13 provides for a tip,
oval in cross-section, the leading edge or point of which, 15, is
sufficiently small and rounded to provide non-damaging insertion
through the larynx, (in the case of an endotracheal tube), or
through the sphincter (in the case of a Foley-type catheter). The
tip may be integral with or otherwise secured to the main body 34
so it is not pulled off upon withdrawing the catheter from the
patient. As shown best in FIGS. 1-4, the proximal and distal edges
16 and 17 of the cuff itself are flush with the outer surface of
the tube 18, fit into recess 19 in the tube 1, and at each end abut
against shoulders 20 and 21, respectively. The tube 1 thus presentS
a smooth, continuous surface which does not have any projecting
shoulders which would cause irritation of tissues upon insertion or
use.
FIG. 2 shows the cuff in its deflated condition, and FIG. 4 shows
the cuff in a partly inflated condition. FIG. 5 illustrates the
method of insertion of the tube 1 with the aid of a laryngoscope
22. After the laryngoscope is removed, air is injected into the
cuff via pilot tube 2 by means of syringe 23. Upon providing
sufficient inflation of the cuff 6', clamp 24 seals off the pilot
tube 2 retaining the balloon inflation. Ventilation of the
patient's lungs can then proceed through the adapter 7 and central
passageway 8.
While the prior art has employed various materials for cuff
balloons, such as rubber latex, relatively hard, non-conformable
silicone rubber, or polyvinylchloride plastics, we use relatively
soft, conformable silicone rubber having a very low durometer and
an elongation factor of in the range of from 1000-1500 percent. A
cuff balloon made from this material requires much less pressure
per unit volumetric expansion than does the above presently used
rubber or plastic materials. For example, a typical rubber or
polyvinylchloride cuff material has a Shore A hardness on the order
of 50, while the physiologically acceptable silicon of our
invention should have a hardness on the order of less than about
20-25. The cuff material of our invention should also have a
tensile strength, in pounds per square inch, of less than about
700-800, and preferably in the range of 500-700, as compared to the
prior art rubber or polyvinylchloride which has a strength of 1,200
psi and greater. Still another parameter critical to our invention
is that the percentage elongation capability should be in the range
of 1,000-1,500 percent. Prior art materials have had a percentage
elongation of from 300-900 percent.
We have also discovered that the stress value must represent as low
a percentage of the breaking stress as possible. For example, a
typical cuff balloon having a deflated diameter of 0.425 inches
will be expanded to the average trachea size of 1.250 inches upon
inflation. The maximum extension required is thus 340 percent of
the original, or 240 percent elongation as normally calculated.
Assuming stress to be directly proportional to strain for typically
used rubber cuff compositions, the stress for prior art types of
cuff materials having percentage elongation on the order of 600
percent is about 400 psi. For the cuff materials of this invention,
having a typical elongation percentage of 1,100, the stress is only
130 psi. This represents a value of 33 percent of the breaking
stresses for the prior art material as compared to 22 percent for
the material of our cuff. The prior art cuff rubber or plastic
material is much nearer its rupture point than the cuff of our
invention, and thus is more apt to break under mechanical
deformation strains. Thus, this stress value of the cuff should be
kept below about 30 percent, and preferably in the range of from
15-25 percent of the breaking stress.
While the tube 1 may be round in cross-section as shown in FIG. 3,
FIG. 7 shows another embodiment in which the tube is generally a
flattened oval in cross-section, more nearly conforming to the
actual shape of the human trachea. Thus, the wall 4 of the tube is
flattened in a ventral-dorsal direction with the side walls 25,25'
being thicker than the ventral wall 26 and the dorsal wall 27.
While the central passageway 8 is shown in FIGS. 3 and 7 to be
circular, it may also be generally oval and concentric with the
outer surface shape 18 (FIG. 7) to provide for walls 4 of
substantially equal thickness throughout. However, the increased
thickness of the side walls 25, 25' provide for convenient
placement of the lumen 3 and the opening 5 into the recess 19 of
the tube 1 for placement of the cuff balloon 6.
FIG. 7 also serves to illustrate a still further embodiment wherein
the balloon wall itself is of preselected unequal or varying
thickness. The ventral portion 28 and the dorsal portion 29 are
shown thickened relative to the lateral or side walls 30, 30'.
Since the side walls are thinner, the balloon tends to expand
unevenly in a controlled fashion with the greater extension in a
lateral direction as compared to that along the ventral-dorsal axis
of the cuff. While FIG. 3 shows a cuff having even wall thicknesses
in conjunction with a generally round tube 4, uneven wall thickness
cuffs as in FIG. 7 may also be used in conjunction with tubes round
in cross-section. In this particular combination, the predetermined
differential thickness of the cuff walls provides for excellent
sealing of the tube in the trachea, even where the main body of the
tube is round. The differentially expansible wall portions of the
cuff compensate for the natural out-of-roundness of the trachea or
for tracheal irregularities in the lateral as compared to the
ventral-dorsal axial direction. In addition, a plurality of
inflation lumens 3 may be used. While one lumen is shown in the
side wall 25' in FIG. 7, it should be understood that another
inflation lumen communicating with an opening to the intra-cuff
space may be placed in the side wall 25.
In preparing the cuff balloon, we prefer to press mold an annular
cylinder of silicone rubber to provide cuff balloon material of the
specific characteristics described above. The cuff is then placed
over an extruded tube having the ventilation and inflation lumens
therein, which tube has been incised to provide recess 19 for
receiving the balloon, and the opening 5 from the recess to the
inflation lumen 3. The proximal and distal margins 16, 17, and
transverse edges of the cylindrical balloon cuff are then coated
with silicone rubber adhesive and placed in the recess, and the
adhesive cured to provide an integral seal between the cuff and the
main tube body 34.
FIGS. 8 and 9 show the principles of our invention adapted to use
in an improved Foley-type urinary catheter with like parts having
the same numbers as in FIGS. 1-5. FIG. 8 shows the cuff 6' in
expanded condition within the urinary bladder walls 31. The cuff 6'
contacts the wall along region 35 as distinct from typical point
(in cross-section) contact of round balloons of the prior art. The
special properties of our silicone rubber permits the expanded cuff
to conform to the walls of the bladder, thus resulting in a lower
perpendicular component of the catheter weight per unit area of the
bladder wall. The conformability of our silicone cuff allows
spreading the weight over a larger area leading to a lower pressure
and less likelihood of severe tissue necrosis. Eye 10 in the
rounded distal tip 12 of the main catheter body communicates with
drain lumen 9 for removal of urine.
FIG. 9 shows the cuff 6 in normal, uninflated condition. The cuff
in longitudinal cross section, i.e., along its axis, is of a
predetermined unevenness in thickness, with the distal end 32 being
thinner than the proximal end 33. This provides for greater
expansion of the balloon at the distal end than the proximal end,
with the result that the balloon is generally triangular in shape,
as seen in FIG. 8, conforming to the natural shape of the urinary
bladder. Thus, by preselected design of wall thickness, the cuffs
of our invention may be adapted to any desired body cavity, vessel,
tube, orifice or the like. While we have described the invention
with respect to several embodiments above, it should be understood
that many variations may be made within the spirit of our
invention.
* * * * *