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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to an instrument for insertion into an animal
body, and, more particularly, concerns a catheter or probe for placement
into various body orifices, and also concerns a method of inserting such
an instrument into an animal body.
Medical instruments, intravascular catheters and the like probes are placed
into various body orifices for many purposes, including the infusion of
fluids, withdrawal of fluid samples from the body, and for the
transduction of other parameters such as pressure, temperature and sound.
Very often, such an instrument has to be placed in a remote part of the
body or perhaps threaded for a considerable distance in the vascular
system. Most catheters of the type for placement, particularly into a deep
body position, are made of a pliable, very flexible, plastic material.
This facilitates any bending or curving that is necessary during placement
and also serves to eliminate or decrease the traumatic effect of its
insertion. However, the relatively low flexural modulus of most catheters
which provides the pliable nature of the catheter, produces at least one
drawback.
A problem arises using most of the very flexible catheters during insertion
of the same into the patient. The tendency of the catheter tubing to
readily bend and flex during the insertion stage oftentimes produces
awkward and erratic threading of the catheter by the operator. This is
especially problematical when the catheter is long and is intended to be
positioned deep in the patient.
Although some probe-like medical instruments have employed pressurization
for various purposes, the variability of the flexural modulus to provide
stiffness during insertion and then flexibility thereafter has not been
disclosed. For instance, U.S. Pat. No. 3,525,329 discloses an evertable,
extensible probe which admits pressure thereinto to extend the probe into
the body cavity to be examined. Along the same lines, U.S. Pat. No.
3,502,069 employs a rigid tubular casing and a flexible evertable tubing
inside. When fluid pressure is admitted into the casing the tubing is
everted out of an open end of the casing. U.S. Pat. No. 3,168,092
describes a probing instrument with a tubing which becomes extraverted
under pressure whereby the tubing exerts pressure on the walls of the
cavity to separate the walls thereof.
Accordingly, it is most desirable to employ a catheter or like instrument
which has a certain level of stiffness or increased flexural modulus of
elasticity in order to facilitate placement of the catheter with relative
ease into the patient. However, as pointed out above, after placement of
the catheter into the final position the stiffness of the same is
undesirable since more pliability and flexibility is required. It can be
seen, then, that it is desirable to be able to vary the degree of
stiffness of catheter tubing so as to have a relatively high degree of
stiffness during placement of the catheter into the patient and then a
relatively low degree of stiffness after final positioning. It is to this
end that the present invention is directed.
SUMMARY OF THE INVENTION
An instrument having a variable flexural modulus for insertion into an
animal body comprises a length of flexible tubing having a normally
relatively low flexural modulus. A lumen inside the tubing provides a free
flow path therethrough. Means is associated with the tubing for
controllably increasing the flexural modulus of the tubing to stiffen the
same during insertion of the tubing into the body. After being positioned
in the body, the means is adapted to allow the tubing to return to its
normally relatively low flexural modulus.
In the preferred embodiment of this aspect of the invention, the means for
increasing the flexural modulus of the tubing includes a second lumen
associated with the catheter tubing. This second lumen has a closed distal
end and a proximal end adapted to be connected to a pressure source. An
increase in pressure in the second lumen serves to increase the flexural
modulus of the catheter tubing, with the pressure being controllable so
that the flexural modulus of the catheter is also controllable. This
second lumen may be a second tubing located inside the catheter tubing,
and, in one embodiment, is removable from the catheter tubing whereby
after the catheter is positioned in the body, the second tubing may be
removable to completely free the fluid path in the lumen.
Another aspect of the present invention includes a method of inserting an
instrument substantially as described above into an animal body. The steps
of the method include increasing the flexural modulus of the catheter
tubing prior to insertion of the same into the body. The stiffened tubing
is then inserted into the body. After the tubing is in position in the
body the method includes decreasing the flexural modulus so that the
tubing returns to its normally relatively low flexural modulus.
In accordance with the principles of the present invention, the catheter
advantageously offers the desirable stiffness characteristic during the
placement or insertion stage into the body, while also providing the
ability to reduce the stiffness after final positioning so that the
catheter may be pliant and flexible. Accordingly, the catheter or like
instrument of the present invention allows the operator to manipulate the
catheter into the patient with relative ease and substantially eliminates
or reduces the awkwardness which accompanies the insertion of catheters
which do not have the variable stiffness feature.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view illustrating the preferred catheter of the
present invention;
FIG. 2 is a cross-sectional view taken along line 2--2 of FIG. 1;
FIG. 3 is a cross-sectional view taken along line 3--3 of FIG. 2;
FIG. 4 is a cross-sectional view of an alternative of the embodiment
illustrated in FIGS. 1-3;
FIG. 5 is a perspective view illustrating another embodiment of a catheter
utilizing the general principles of the present invention;
FIG. 6 is a cross-sectional view taken along line 6--6 of FIG. 5; and
FIG. 7 is a cross-sectional view similar to that of FIG. 6 illustrating the
catheter in its increased condition of flexural modulus.
DETAILED DESCRIPTION
While this invention is satisfied by embodiments in many different forms
there is shown in the drawings and will herein be described in detail a
preferred embodiment of the invention, with the understanding that the
present disclosure is to be considered as exemplary of the principles of
the invention and is not intended to limit the invention to the embodiment
illustrated. The scope of the invention will be pointed out in the
appended claims.
Adverting to the drawings, particularly to FIG. 1, there is illustrated a
catheter 10 for insertion into a body orifice, particularly suitable for
infusing fluids, withdrawing fluid samples from the body or for the
transduction of other parameters such as pressure, temperature and sound.
Catheter 10 includes an elongate slender length of catheter tubing 12
which is preferably made of plastic and has a normally relatively low
flexural modulus. This imparts a high degree of flexibility and pliability
with a concomitantly low degree of stiffness. As pointed out above, this
flexibility feature is desirable especially when catheter tubing 12 is
very long, so that the tubing may be able to bend and curve into the body
orifice and be finally positioned where intended. At the proximal end of
tubing 12 it is connected to a hub 14, such as a female Luer connector,
for attachment to the monitoring or feeding source.
As seen more clearly by referring to FIGS. 2 and 3, in conjunction with
FIG. 1, catheter tubing 12 is a thin-walled tubing having its distal end
16 tapered inwardly in order to facilitate the insertion of this end into
the body. Catheter tubing 12 is hollow along its longitudinal dimension
thereby providing a first lumen 18 inside which provides a free path for
the flow of fluids or other measurement parameters through the tubing. To
this end, distal end 16 includes a hole 19 communicating with first lumen
18 in order to keep that end of the first lumen open. At the other end of
tubing 12, hub 14 has a passageway 20 therein which communicates with
first lumen 18. Thus the fluid path is open between hole 19 in the distal
end of the tubing through first lumen 18 and out passageway 20, or vice
versa if fluid flows the opposite direction. Located inside catheter
tubing 12 substantially along its entire length and substantially parallel
to the first lumen is a second lumen 21. In the embodiment being
described, second tubing 21 has a closed distal end 22 while its proximal
end 24 is connected to a pressure source 25. Thus, first lumen 18 and
second lumen 21 are two separated passageways, the former being completely
open for the free passage of fluids, the latter being closed and admitting
air or other fluids therein from a source in order to stiffen the flexural
modulus of the tubing. This operation will be described hereinafter. To
assure that second lumen is adequately closed at both ends, a seal plug 26
may be fit into the proximal end of second lumen if that end would
normally have been open as a result of the fabrication of the catheter
tubing.
Instead of employing two separate lumens, one for pressurization, two
separate tubings may also be used, such as the concentric configuration as
illustrated in FIG. 4.
In this alternate embodiment, catheter 30 includes catheter tubing 31 and a
hub 32 connected to catheter tubing 31. Hub 32 may be a standard female
tapered Luer connector. Catheter tubing 31, similar to the above-described
embodiment, has a normally relatively low flexural modulus so as to be
very flexible and pliant. The catheter tubing is hollow and includes a
lumen 34 therethrough to provide a free path for fluid flow. Surrounding
catheter tubing 31 is a second tubing 35; an annular clearance space 36 is
provided between the inside wall of second tubing 35 and catheter tubing
31. The distal end 38 of the second tubing is tapered in point-like
fashion in order to facilitate insertion of the catheter into the patient.
At distal end 38 a seal is made with the distal end 39 of catheter tubing
31 so that annular space 36 is closed at the respective distal ends of the
tubings. Thus, fluid to or from the body is only allowed to pass through
lumen 34 inside the catheter tubing. At the proximal end of second tubing
25 a connection 40 is provided to pressure source 41. Since, in the
embodiment being described, connection 40 is provided at a right angle,
the rear portion 42 of the catheter is appropriately closed to effectively
contain the inflow of the pressurized medium. It can be seen that the
pressure of annular space 36 is increased by the pressure flowing in from
pressure source 41 with the result that the flexural modulus of catheter
tubing 31 is increased. This stiffens the catheter during the insertion
and placement stage. After final positioning, the pressure is reduced
whereby the normally relatively low flexural modulus of the catheter
tubing remains with its normal flexibility. It is appreciated that second
tubing 35 surrounding catheter tubing 31 is also flexible and pliant in
its normal, relaxed condition so as to be compatible with the catheter
tubing.
In operation, and returning to the preferred embodiment of FIGS. 1 to 3,
the pressure source is appropriately connected to second lumen 21 prior to
insertion of the catheter into the patient. The flexural modulus of the
catheter tubing is increased at this time by increasing the pressure
inside second lumen 21. A noticeable stiffening effect is observed and
felt by the operator of this catheter. In the stiffened condition, the
catheter tubing is inserted into the boby of the patient and placed or
threaded into the appropriate position. When this step is completed, the
pressure source is controlled to de-pressurize the atmosphere inside
second lumen 21. In turn, this causes a decrease in the flexural modulus
of the catheter tubing so that it then returns to its normally relatively
low flexural modulus. Following this step, the appropriate attachment may
be made to utilize this catheter for its intended purpose.
Another embodiment of the present invention utilizing the same general
principles as the previous embodiments is illustrated in FIGS. 5-7.
Catheter 50 includes an elongate slender catheter tubing 52 which normally
has a relatively low flexural modulus. Catheter tubing 52 is preferably
thin-walled with its distal end 56 tapered inwardly to facilitate
insertion of this end into the body. This tubing is hollow along its
longitudinal dimension thereby providing a lumen 58 inside which provides
a free path for the flow of fluids or the like. A hole 59 in the distal
end communicates with lumen 58 to keep that end of the tubing open. At the
proximal end of tubing 52, a hub 54 is provided, including a connector 55
thereon. A passageway 60 in the connector communicates with lumen 58.
Positioned inside catheter tubing 52 substantially along its entire length
is a second tubing 61. This second tubing has a closed end 62 while is
proximal end 64 is adapted to be connected to a pressure source 65. As
seen particularly in FIGS. 6 and 7, both catheter tubing 52 and second
tubing 61 are in the normally relaxed condition; catheter tubing 52 is
normally relatively flexible with a low flexural modulus, and second
tubing 61 is positioned in lumen 58 so that its distal end 62 faces the
insertion end of catheter tubing 52. It is noted that there is an annular
clearance between second tubing 61 and the inside wall of catheter tubing
52 so that, if second tubing 61 is to remain permanently in the catheter,
the fluid is free to pass through the lumen through the path previously
described. It should be pointed out that if second tubing 61 is to remain
in the catheter during fluid flow, the rear portion 65 of hub 54 should be
appropriately closed so that fluid may effectively flow out of passage 60
in connector 55 rather than out the rear portion in the embodiment being
described. Of course, various hub and connection arrangements may be
designed which are within the purview of the intended function of the
present invention, and which may vary from the particular version
illustrated and described.
Turning now to FIG. 7, second tubing 21 is preferably expandable under
pressure so that when the same is pressurized it provides a snug fit
against the inside wall of catheter tubing 52. At the same time, distal
end 62 of the second tubing protrudes slightly out of the insertion end 56
of the catheter tubing; by virtue of its radial expansion, distal end 62
covers the corners of the distal tip of the catheter tubing rendering a
relatively smooth tip, free of sharp corners, which will further aid in
threading of the catheter and reduce the risk of blood vessel wall or body
orifice wall irritation. The pressure to be delivered from pressure source
65 may be either liquids or gases in order to increase the pressure inside
second tubing 61. While this increased pressure is maintained, it can be
appreciated that the flexural modulus of catheter tubing 52 is increased
with the result that the catheter tubing has a higher level of stiffness.
This, in turn, provides improved manipulation of the catheter tubing
during the placement stage into the body. Once the final, desired position
is reached, the controllable pressure from pressure source 65 is reduced
thereby returning second tubing 61 to its unexpanded state as that of FIG.
6, while also returning catheter tubing 52 to its normally relatively low
flexural modulus. At this time, a suitable connection may be made to
connector 55 in order to utilize this catheter for its intended purpose.
While the embodiments of FIGS. 5 to 7 are concerned with a catheter in
which second tubing 61 is permanently positioned therein, a slight
modification of this embodiment will allow second tubing 61 to be removed
after final positioning. In this modification, rear portion 65 of hub 54
is not necessary since second tubing 61 will merely lie inside lumen 58
during the placement and pressurization periods. Thereafter, second tubing
61 is removable from the inside of catheter tubing 52 thereby completely
freeing the fluid path in lumen 58. In this modification, connector 55 may
also be eliminated, hub 54 serving as the connection medium to which the
appropriate device is to be connected. Hub 54, in this instance, may
typically be a standard female Luer connector.
Thus, a medical instrument for insertion into an animal body has been
provided with a variable flexural modulus to stiffen the same during
insertion and placement into the body, and to relax and render pliable and
flexible the catheter after the same has been finally positioned.
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