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BACKGROUND
U.S. Pat. No. 3,995,623 discloses a multi-lumen flow-directed catheter
suitable for use in diagnosing cardiovascular and pulmonary diseases. When
the catheter is used for thermodilution measurements, a bolus of cold
liquid is injected into the right atrium or superior vena cava (through
port 30) and the resultant change in blood temperature is detected by a
thermistor (represented by numeral 35) in the pulmonary artery, such
change in blood temperature being representative of cardiac output. Three
lumens are required by the patented construction to achieve such
operation, one lumen conducting gas for balloon inflation, another
conveying liquid for the injection of the cold bolus (or for right atrium
pressure monitoring, blood sampling, or infusion of therapeutic media) and
a third carrying the thermistor leads. One or more additional lumens would
be provided where further capabilities are desired; thus, the patent
discloses a fourth lumen (C) which extends completely through the catheter
body for use in measuring pulmonary arterial pressures when the catheter
is in place and the balloon is deflated, or pulmonary capillary wedge
pressures when the balloon is inflated.
While the multiple function capability is an important objective,
especially for heart catheterization where it is desirable to obtain as
much diagnostic information as possible in a single catheterization
procedure, such an objective has been achieved in the past either by
increasing the size (outside diameter) of such a catheter or by reducing
the cross section of each lumen and, hence, lowering the performance
characteristics of the catheter. Not only must the lumens be made smaller,
if their number is to be increased without altering the catheter's outside
dimensions, but the necessity of providing septa between the lumens
requires a further reduction in lumen size. Even when the partitions or
septa which define the multiple lumens are made as thin as possible, their
thickness still substantially reduces the space available for the several
lumens within a catheter of any given size. At the same time, the outside
dimensions of such a catheter, which must be capable of passing through
the vascular system without injury to the patient, must be kept as small
as possible. A 4 French catheter (approximately 0.053 inch O.D.) would
therefore generally be considered more desirable than a larger 6 French
(0.078 inch O.D.) catheter in terms of ease of manipulation, and reduced
risk of possible complications in use. Consequently, in order to achieve
multiple functions in a cardiac catheter of optimum size, it has generally
been considered necessary to compromise the performance capabilities of
such a catheter.
Other U.S. Pat. Nos. disclosing multiple-lumen catheters are 3,746,003,
3,833,004, 3,710,781, 3,634,924, 3,152,592, 3,044,468, 3,050,066, and
2,845,930.
SUMMARY
This invention lies in part in the discovery that in the construction of a
catheter having a proximal port for cold bolus introduction (or for blood
sampling or pressure measurements) and a distal thermistor or other
electrical element, the two lumens used for such purposes may also be
adapted for joint use as a gas pathway or chamber, thereby eliminating a
third separate lumen previously thought to be necessary for the latter
purpose. Since the space which such a lumen would have occupied may be
used to increase the cross sectional dimensions of the other lumens, and
since the space which would have been occupied by a septum needed for the
purpose of defining a separate gas-transmitting lumen also becomes
available, the result is that a catheter made in accordance with this
invention would have superior flow capacity and other performance
characteristics when compared with a conventional catheter of similar
outside dimensions. Viewed differently, the present invention makes it
possible to reduce substantially the outside dimensions of a plural-lumen
catheter without at the same time reducing its performance
characteristics.
Such objectives have been achieved by eliminating the separate lumen which
would contain gas required in connection with the operation of pressure
responsive means adjacent the distal end of the catheter and by providing
a gas pathway through portions of the other lumens in such a manner that
the electrical leads remain isolated from possible liquid contact. In the
disclosed embodiment, the gas pathway extends through the lumen containing
the electrical leads from the proximal end of the catheter to an
intermediate point, at which point the pathway extends through an aperture
in the longitudinal septum separating the lead-containing lumen from a
second lumen used for bolus injection and other diagnostic functions. The
gas pathway then continues through the second lumen to a distal point
where a balloon or other pressure responsive element is located. Liquid
cannot enter either the distal portion of the second lumen or any portion
of the first lumen because of a sealant plug in the second lumen adjacent
to the port for bolus discharge. At the same time, the sealant plug is
formed and/or located to maintain the distal portion of the second lumen
in flow communication with the first lumen through the aperture in the
longitudinal septum.
In practicing the method of the invention, a lateral port may first be
formed in the outer wall of the catheter body at an intermediate point,
the port being located so that it communicates only with the lumen of the
catheter intended to convey liquid for bolus injection, blood sampling, or
pressure measurements. A suitable tool may then be inserted through the
port to form an aperture in the septum which separates the lumen for
liquid flow from a parallel lumen intended to contain the electrical
leads. In one form of the invention, the aperture is located just distal
to the port, a procedure which may be readily accomplished by inserting
the tool through the port at an angle so that the tip of the tool pierces
the septum at a distally-offset point. In another embodiment of the
invention, the aperture is positioned generally within the longitudinal
limits of the port; that is, the aperture is in general radial alignment
with the port. In either case, a sealant plug is then located within the
second lumen (the liquid-transmitting lumen) in such a way that liquid is
blocked from entering that portion of the second lumen distal to the port
and from entering the first lumen through the aperture in the septum. Such
a sealant plug may either be formed in situ or may be pre-formed and
secured in place through the lateral port in the catheter body.
Other objects and advantages of the invention will be apparent from the
specification and drawings.
DRAWINGS
FIG. 1 is a somewhat diagramatic sectional view illustrating a
flow-directed catheter of this invention when such a catheter is
positioned for use.
FIG. 2 is a side elevational view of the catheter.
FIG. 3 is an enlarged broken longitudinal sectional view of the distal
portion of the catheter.
FIG. 4 is a cross sectional view taken along line 4--4 of FIG. 3.
FIG. 5 is an enlarged cross sectional view taken along line 5--5 of FIG. 3.
FIG. 6 is an enlarged cross sectional view taken along line 6--6 of FIG. 3.
FIGS. 7 and 8 are somewhat schematic views illustrating a sequence of steps
in performing the method of this invention.
FIG. 9 is a fragmentary exploded perspective view illustrating a second
embodiment of this invention, such view depicting a pre-formed sealant
plug as it is being moved into position within the catheter body.
FIG. 10 is a fragmentary perspective view of the embodiment of FIG. 9
showing the sealant plug in fully inserted position.
DETAILED DESCRIPTION
FIG. 1 illustrates a catheter 10 extending to the right side of a patient's
heart H. In brief, the parts of the heart and their operation are as
follows: the right atrium 12 receives blood from the superior and inferior
vena cava veins 13 and 14 and pumps such blood into the right ventricle 15
through the tricuspid valve 16. From the right ventricle, the blood
travels to the lungs through pulmonary valve 17 and pulmonary artery 18.
Oxygenated blood returning from the lungs enters left atrium 19 and then
passes through mitral valve 20 into right ventricle 21. The blood leaves
the heart through aorta 22 after passing through aortic valve 23.
Catheter 10 is depicted as a multi-purpose flow-directed catheter having a
tubular body 11 equipped at its distal end with pressure responsive means
in the form of a balloon 26. At its proximal end, the catheter body
terminates in a coupling 27 which operatively connects the lumens of the
catheter to connector tubes 28, 29, and 30. Connector tube 29 bifurcates
to provide branches 29a and 29b and, as well known in the art, all of the
tubes or branches are provided with coupling elements 31-34 for attaching
the connector tubes to syringes or other devices.
The structure as so far described is essentially conventional. In use, the
soft, pliable catheter body is introduced into the vascular system from
the antecubital, femoral, subclavian, or jugular areas and is advanced,
with the balloon in deflated or only partially inflated condition, into
the right atrium 12. The balloon is then inflated to its maximum
recommended capacity and the flow of blood through the heart rapidly
propels the inflated balloon-tipped catheter from the right atrium into
the pulmonary artery 18 (FIG. 1). It will be observed that when the
catheter is so positioned, balloon 26 has advanced through the pulmonary
artery into what is generally referred to as the pulmonary capillary wedge
position, a sensor or other electrical element 35 at the distal end
portion of the catheter body (just proximal to the balloon 26) is disposed
within the pulmonary artery, and a lateral flow port 36, sometimes
referred to as a proximal port (in contradistinction to distal port 37 at
the tip of the catheter body distal to the balloon) is positioned within
right atrium 12. With the catheter so positioned, a variety of diagnostic
procedures may take place, all of which are well known and, therefore,
will be described only briefly here. Port 36 may be used for taking
pressure measurements from the right atrium, for injecting or infusing
solutions, or for taking blood samples, whereas distal port 37 may also be
used for sampling, infusion or injection, or measuring pulmonary artery
and pulmonary capillary wedge pressures (depending on whether such
measurements are taken with balloon 26 inflated or deflated). In
thermodilution measurements, a sterile, cold solution is injected into the
right atrium through port 36 and the resulting change in blood temperature
is detected by thermistor 35, thereby allowing calculation of cardiac
output.
It is to be understood that the electrical element 35 need not be in the
form of a thermistor; it may, for example, be an electrode for sensing
(or, if necessary, stimulating) electrical activity of the heart as
disclosed in detail in co-owned U.S. Pat. No. 3,995,623. However, unlike
the construction disclosed in that patent, which has four lumens extending
through the catheter body, the catheter of the present invention is
capable of performing the same functions with only three lumens.
As shown in FIG. 4, catheter body 11 is divided by a three-branched
partition or septum 40 so that it defines three parallel lumens 41, 42,
and 43. Lumen 41 is a through lumem which communicates with connector tube
28 and which extends all of the way to distal port 37. Such a lumen is
illustrated because of the functions already described with which such
distal port is associated; if such functions are regarded as unnecessary,
then it is to be understood that through lumen 41 may be eliminated and
the sapce that would otherwise be occupied by that lumen may be used for
increasing the size of lumens 42 and 43, or for providing a lumen intended
to perform some other purpose, or for reducing the outside cross sectional
dimensions of the catheter body.
Lumen 42 is a passage which communicates with connector tube 29 and which
contains electrical leads 44 extending to the electrical element 35
located within the lumen near balloon 26. As shown most clearly in FIG. 3,
the element 35, which takes the form of a thermistor, is embedded in a
suitable embedding medium 46 adjacent an opening 47 formed in the outer
wall of the catheter body. Any appropriate embedding medium may be used.
Lumen 43 is the lumen which carries liquids to or from proximal port 36. As
indicated, that port is so named because it is a substantial distance from
the tip of the catheter and from distal port 37; however, as shown in FIG.
2, port 36 is actually located in an intermediate position. Thus, in a
typical catheter having a total body length of approximately 110
centimeters, the distance between the proximal lumen and the distal tip
would ordinarily fall within the rnge of approximately 15 to 35
centimeters, such distance being selected so that, when the catheter is
positioned as shown in FIG. 1, port 36 will be disposed in the right
atrium or superior vena cava.
At its proximal end, lumen 43 communicates with connector tube 30 and
coupling 34. As already stated, lumen 42 communicates with connector tube
29. Leads 44 extend from that lumen into connector tube 29, branch 29b,
and coupling 33. As is well known, coupling 33 may be connected to a
thermodilution cardiac output computer or, should electrical element 35
take the form of an electrode rather than a thermistor, to other
appropriate electronic equipment.
Portions of both lumens 42 and 43 are used to define the flow passage for
gas for inflating and deflating balloon 26. The gas of choice is carbon
dioxide because of its relatively rapid diffusion rate in blood should the
balloon rupture; however, it is conceivable that other gases might be used
or even recommended under special circumstances. Furthermore, while a
balloon is represented in the drawings and described in detail herein for
purposes of illustration, other types of pressure responsive means might
be substituted. For example, the pressure responsive means might take the
form of a diaphragm-equipped pressure transducer for measuring blood
pressure at or near the tip of the catheter, the trans-luminal gas pathway
in such a case serving to vent the inside surface of the diaphragm to
atmosphere.
Where the pressure responsive element 26 comprises a balloon as shown, the
gas enters and leaves the balloon chamber through a lateral port 48 formed
in the wall of catheter body 11 (FIG. 3). The balloon 26 may be secured in
place in any suitable manner, reference being made to U.S. Pat. Nos.
3,995,623, 3,746,003, and 3,833,004 for further information in that
regard. Since balloon-attachment methods and constructions are well known
in the art and and form no part of the present invention, a more detailed
description is believed unnecessary herein. It should be noted, however,
that the balloon is shown in its fully deflated condition in FIG. 3 and
FIG. 2 (solid lines) and in fully inflated condition in FIG. 1 and in FIG.
2 (phantom lines).
Septum 40 is provided with an aperture 49 that places lumens 42 and 43 in
flow communication. In the embodiment depicted in FIG. 3 that aperture 49
is located in close proximity to port 36; more specifically, just distal
to the port. A sealant plug 50 is located lumen 43 between port 36 and
aperture 49 and performs the multiple functions of sealing the distal
portion of lumen 43 against the ingress of liquid, blocking the flow of
liquid on the proximal side of the plug from entering lumen 42 through
aperture 49, and maintaining the distal portion of lumen 43 (i.e., the
portion distal to port 36) in open communication with that portion of
lumen 42 proximal to element 35. If the catheter body is formed of
polyvinyl chloride, than a sealant plug material composed of has been
found effective; however, it is to be understood that any of a variety of
materials may be selected for the catheter body and for the sealant plug.
From the foregoing, it is believed apparent that the catheter of the
present invention requires one less lumen than prior catheters to achieve
the same monitoring or diagnosing functions, and that the elimination of
one lumen permits size adjustments which result in either improved
performance characteristics, or smaller external size, or both. For
example, it has been found that a three-lumen catheter of the present
invention of 4 French size has performance characteristics (flow capacity
and frequency response) approximating those of a substantially larger
(outside diameter) prior art four-lumen catheter of size 6 French.
The wires or leads 44 for electrical element 35 are insulated although such
insulation is intended primarily to prevent the conductors for making
electrical contact with each other since the sealant plug 50 effectively
prevents liquid from invading lumen 42 through port 36 or from the
proximal portion of lumen 43. The leads are also protected against contact
with blood flowing into lumen 42 should balloon 26 rupture in use because
blood entering lumen 43 in the vicinity of the balloon would clot and seal
lumen 43 long before reaching aperture 49.
Certain steps of fabricating the catheter are illustrated in FIGS. 7 and 8.
After the proximal port 36 has been formed in the catheter body at a point
intermediate its length, an aperture-forming tool 55 is inserted through
the port and into contact with septum 40 (FIG. 7). In the method shown,
the tool is inserted at a forwardly-directed angle in order to form
aperture 49 at a point distal to port 36. The tool or probe may be heated
to cause the thermoplastic material of septum 40 to melt upon contact and
thereby develop aperture 49, although it is believed apparent that other
cutting or piercing techniques may be used to form that aperture.
After aperture 49 has been formed, sealant may be injected from a nozzle 56
into lumen 43, again using port 36 as an access opening (FIG. 8). Upon
solidification, the sealant forms plug 50 which seals the distal portion
of lumen 43 from any liquid invasion from port 36 or the proximal portion
of lumen 43 and, at the same time, maintains the distal portion of lumen
43 in direct communication with lumen 42 through aperture 49. Preferably,
the trailing surface of plug 50 is contoured as shown in FIG. 3 to help
direct the flow of liquid exiting port 36 (and discharged from a syringe
connected to coupling 34 and connecter tube 30) or entering that port for
the taking of samples or pressure measurements. In the case of pressure
measurements, it is to be understood that couplings 41 and/or 34 would be
connected to any of a variety of pressure measuring devices rather than to
syringes.
While the method disclosed herein necessarily involves the use of port 36
as an access opening for the formation of aperture 49, it is not essential
that the aperture be formed on the distal side of the port, especially if
the sealant plug is pre-formed as indicated in FIGS. 9 and 10. In FIG. 9,
it will be seen that sealant plug 50' is pre-formed to fit within port or
opening 36' in the wall of catheter body 11'. Aperture 49', which may be
substantially smaller than port 36' (since the aperture is required only
to transmit gas for balloon inflation and deflation), may be located
within the axial limits of port 36'.
The pre-formed plug 50' is dimensioned to fit within the area of lumen 43'
outlined by opening 36' and, when sealed in place by a suitable solvent,
cement, or other suitable means, appears as shown in FIG. 10. The plug is
formed with two passages, one passage 60 extending from face 61 to the
distal end 62 and being aligned with aperture 49' when the parts are
assembled for the purpose of placing that aperture (and lumen 42') in
communication with the portion of lumen 43' distal to the plug. The second
passage or recess 63 simply contributes in defining the flow port and, as
shown most clearly in FIG. 10, helps to direct liquid into or out of the
proximal portion of lumen 43' without allowing such liquid to enter other
lumens or any portions of the catheter distal to the plug.
While in the foregoing I have disclosed embodiments of the invention in
considerable detail for purposes of illustration, it will be understood by
those skilled in the art that many of these details may be varied without
departing from the spirit and scope of the invention.
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