Note: Descriptions are shown in the official language in which they were submitted.
D-1565
1-11-84 1 æ~lL403Ç
BACKGROUND OF THE INVENTION
Various medical procedures require the
measurement of the temperature of a fluid, such as blood,
flowing within a body. For example, to make thermodilution
measurements, a bolus of cold liquid is injected into the
right atrium or vena cava, and the resulting change in
blood temperature is measured in the pulmonary artery. The
temperature measurement is made by a thermistor which is
carried by a thermodillltion catheter. U.S. Patent Nos.
3,995,623; 4,105,022; and 4,329,994 show different
techniques for mounting a thermistor on a catheter.
Thermodilution blood temperature measurements do
not require that the thermistor have a very rapid response.
However, for some medical procedures, such as the
calculation of ejection fraction, it is necessary to
measure changes in blood temperature as they occur. In
this event, it is necessary or desirable that the
thermistor measure blood temperature directly rather ~han
the temperature of the catheter on which it is mounted.
Specifically, the thermistor should follow the beat-to-beat
blood temperature changes so that discrete steps in the
temperature curve can be observed. Unfortunately, the
patented constructions identified above prevent the
thermistor from having an adequately rapid response.
SUMMARY OF THE INVENTION
This invention provides for the mounting of a
thermistor so that it has a very rapid response. With this
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invention, the thermistor can track temperature changes
about one-half as rapidly (twice the effective time
constant) as the thermistor could track temperature changes
if it were not mounted on a probe or catheter-type carrying
5 apFaratus. Conventional thermistor mounts typically
respond less than one twentieth (l/20j as rapidly (20 times
the effective time constant) as an unmounted thermistor.
The apparatus of this invention, which may be,
for example, a probe or a catheter, includes an elongated
tube sized to be received within a vein or artery and
having proximal and distal ends, a peripheral wall, at
least one lumen extending longitudinally within the tube
and an opening in the peripheral wall which extends from
the lumen to the exterior of the tube. In order to follow
the increments of temperature change, a thermistor is
mounted in an essentially exposed condition adjacent the
opening of the tube. The thermistor can advantageously be
mounted by a thermistor mounting body located in the lumen
adjacent the opening. The thermistor mounting body
cooperates with the tube to at least partially define a
cavity which opens radially outwardly at the opening. In
order to expose the thermistor, the thermistor is only
partially within the mounting body and projects radially
outwardly of the mounting body into the cavity. To assure
that the fluid flowing along the tube can contact the
projecting portion of the thermistor, the cavity is much
larger than the thermistor so that the thermistor is spaced
from the wall of the cavity over a major area of the
cavity. Accordingly, the portion of the thermistor which
30 projects into the cavity is in good heat transfer
relationship to the fluid, the temperature of which is to
be measured.
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The thermistor has a major or lon~ axis and a
minor or shor~ axis. To further assist in providing the
thermistor with a rapid response, the thermistor is
preferably mounted with the major axis generally transverse
to the adjacent portions of the longitudinal axis of the
lumen. For optimum results, the major axis extends
perpendicular to the axis of the lumen and generally
perpendicular to the direction of fluid flowing along the
tube.
To make the thermistor saline resistant, a
relatively thin layer of insulating material preferably
covers at least the portion of the thermistor which is in
the cavity. This layer is made as thin as possible so as
to minimize the extent to which it reduces heat transfer
between the fluid and the thermistor. Thus, this layer is
substantially thinner than the mounting body. The mounting
body is preferably constructed of a material having good
heat insulation properties so as to retard heat transfer
between the thermistor and the other portions of the
apparatus. Accordingly, the thermistor is made to respond
essentially, or primarily, to temperature changes of the
fluid and only to a very minimal degree to temperature
changes of the apparatus.
The thermistor is typically a small and somewhat
fragile element. To protect the thermistor from shearing
off when, for example, the apparatus is withdrawn from a
tubular introducer, the thermistor preferably does not
extend radially outwardly of the cavity. Stated
differently, the tube has a body line, and the thermistor
extends radially outwardly no farther than about such body
line.
In a preferred construction, the apparatus also
includes first and second plugs in the lumen on opposite
sides of the mounting body, and the mounting body at least
- assists in retaining the plugs in the lumen. To securely
5 mount the thermistor and to provide adequate saline
protection without covering too much of the thermistor's
exterior surface, the mounting body preferably covers no
more than about one half of the exterior surface of the
thermistor.
In a preferred construction, the apparatus
includes at least one thermistor lead coupled to the
thermistor. The lead has an axial portion which extends
along t~e lumen and a radial portion joined to the axial
portion and extending generally transverse to the axial
15 portion at the cavity. The radial portion is joined to the
thermistor. In this fashion, the thermistor can be mounted
with its major axis extending generally transverse to the
axis of the lumen.
The invention, together with additional features
20 and advantages thereof, may best be understood by reference
to the following description taken in connection with the
accompanying illustrative drawings.
25 BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is an elevational view of a catheter
constructed in accordance with the teachings of this
30 invention.
(33
Fig. 2 is an enlarged sectional view taken
generally along line 2-2 of Fig. 1.
Figs. 3-5 are enlarged, longitudinal sectional
views taken on an axial plane illustrating the portions of
the ca~heter adjacent the injectate port, the thermistor,
and balloon, respectively. Fig. 4 is taken generally along
line 4-4 of Fig. 2.
Fig. 6 is an enlarged fragmentar~ sectional view
'aken generally along line 6-6 of Fig. 4.
Fig. 7 is a sectional view of the human heart
showing one example of how the apparatus of this invention
can be used.
OESCRIPTION OF THE PREFERRED EMBODIMENTS
Fig. 1 shows an apparatus in the form of a
catheter 11 which comprises an elongated catheter tube 13
having a balloon inflation lumen 15 (Fig. 2~, a through
lumen 17 and an injectate lumen 19. A pressure monitoring
tube 21 and an injectate tube 23 are fused to the tube 13
within the through lumen 17 and the iniectate lumen 19,
respectively. A tube 25 is fused to the tube 13 within the
lumen 15 and is joined to an inflation tube 27 and a
conduit 29 for thermistor leads 31 by a coupler 33. The
proximal end of the catheter tube 13 and the distal ends of
the tubes 21, 23 and 25 are encased by a flexible sleeve
35.
3~ The catheter tube 13 may be extruded from a
suitable biocompatible plastic material. The catheter tube
13 is flexible, elongated and sized to be received within a
vein or an artery. The catheter tube 13 has a proximal ena
37 and a distal end 39.
The balloon inflation lumen 15 extends
continuously from the proximal end 37 through a port 40
(Fig. 5) to a balloon 41 closely adjacent the distal end
39. The balloon 41 and the manner in which it is inflated
through the balloon inflation lumen 15 is conventional.
The through lumen 17 extends continuously from
the proximal end 37 to the distal end 39 where it opens at
a distal port 43 (Fig. 5). The through lumen 17 can be
used, for example, to monitor pressures within the body.
The injectate lumen 19 extends continuously from
the proximal end 37 to a location distally of a thermistor
45. For example, the thermistor may be 1.45 inches to 1.65
inches from the distal end 39. An injectate port 47 (Figs.
1 and 3) extends through a peripheral wall 49 of the
catheter tube 13 to provide communication between the
injectate lumen 19 and the exterior of the tube.
Accordingly, a liquid injectate can be injected through the
injectate tube 23, the injectate lumen 19 and the injectate
port 47 into the patient. For example, the in j ectate port
47 may be 8.17 inches to 8.37 inches from the distal end
39. of course, the catheter 11 can be provided with
additional lumens, if desired, to provide additional
functions for the catheter.
A plug 51 of a suitable plastic material and a
mass of urethane adhesive 56 are provided in the injectate
lumen 19 just distally of the injectate port 47 to
completely close off the lumen 19 distally of the injectate
port. In this example, the thermis.or leads 31 extend from
the conduit 29 through the tube 25 and the
balloon inflation lumen 15 to a location adjacent the plug
51. From there, the leads 31 pass through a sealed opening
53 in a partition 55 between the lumens 15 and 19 and
between the plug 51 and the partition 55 into the injectate
lumen 19 distally of the plug. Of course, the cross over
of the leads 31 between lumens is optional.
The leads 31 extend through the lumen 19 to the
thermistor 45 as shown in Fig. 4. Each of the leads 31 has
an axially extending portion 59 which extends axially of
the lumen 19 and a radially extending portion 61 which
extends perpendicular to the portions 59 and joins the
portions 59 to the thermistor 45.
Thermistor 45, which in this embodiment is a
bead-type thermistor, has a major axis 63 and a minor axis
65 (Fig. 6), with the major axis being much longer in this
embodiment than the minor axis. The major axis 63 is
generally parallel to the radially extending portions 61.
The thermistor 45 is completely covered with, and
encapsulated in, a thin layer 67 of electrical insulating
material, such as one or more thin coatings of vinyl and/or
urethane to provide saline protection.
The peripheral wall 49 has an opening 69, and the
thermistor 45 .is mounted in a radially extending ~one which
includes this opening. The thermistor 45 is mounted by a
mounting body 71 which is in the lumen 19 adjacent the
opening 69. The mounting body 71 cooperates with the tube
13 to define a cavity 73 at the opening 69 which opens
radially outwardly.
The mounting body 71 may be constructed of
urethane or other suitable biocompatible electrical and
thermal insulating adhesive material. The thermistor 45 is
partially ~ithin the mounting body 71 and projects radially
outwardly of the mounting body into the cavity 73. The
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cavity 73 has an outer wall 75 and the cavity 73 is much
larger than the thermistor 45 so that the thermistor 45 is
spaced from the wall 75 of the cavity over a major area of
the wall. Thus, only a ~ery small percent of the volume of
the cavity 73 is occupied by the thermistor.
The thermistor 45 is greatly enlarged in Figs. 4 and 6 for
clarity. The opening 69 and the cavity 73 are sufficiently
large so that fluid'flowing along the tube 13 can readily
flow over the portion of the thermistor 45 which projects
radially outwardly of the mounting body 71. Because the
projecting portion of the thermistor 45 is covered only by
the thin layer 67, the projecting portion of the thermistor
is in good heat transfer relationship to the fluid flowing
along the tube 13.
As shown in Figs. 4 and 6, the thermistor 45 is
mounted with the major axis 63 extending perpendicular to
the longitudinal axis of the lumen 19 and, hence, generally
transverse to the fluid flowing along the tube 13.
Accordingly, the thermistor 45 projects as far as possible
into the fluid stream flowing along the tube 13, and
maximum heat transfer is obtained.
The peripheral wall 49 has an outer peripheral
surface 77, and the outline of that surface over the
opening 59 is a body line 79 of the tube 13. The
thermistor 45 extends radially outwardly -no farther thàn
about the body line 79 and, in the embodiment illustrated,
lies slightly radially inwardly of the body line. Thus,
the thermistor 45 does not extend out of the cavity 73.
Plugs 81 and 83 (Fig. 4) are provided in the
lumen 19 in opposite sides of the mounting body 71. The
plugs 81 and 83 completely block the lumen 19 on opposite
.. _ . . .. . . .. . .
sides of the opening 69, and the plug 81 has a sharply
inclined face 85 which provides ample room for the radially
extending portions 61 of the thermistor leads 31.
Because the mounting body 71 i5 constructed of an
adhesive material, it can be used to adhere the plugs 81
and 83 in position. Specifically, the plugs 81 and 83 are
inserted into the lumen 19, and after the thermistor 45 is
in position, the adhesive is poured between the plugs
around the thermistor and allowed to cure to form the
mounting body 71. The plugs 81 and 83 serve to confine the
mounting body 71 while it is curing. By constructing the
mounting body 71 of an adhesive material which will
strongly bond to the layer 67, and preferably the same
adhesive insulating material which forms the outer portions
of the layer 67, a saline-tight joint is formed between the
mounting body and the layer 67 which prevents the ingress
of saline.
The mounting body 71 co~ers no more of the
exterior surfa~e area of the thermistor 45 than is
necessary to mount the thermistor and to provide saline
protection. In the embodiment illustrated, the mounting
body 71 covers no more than about one half of the exterior
surface of the thermistor.
The mounting body 71 thermally insulates the
thermistor 45 from the adjacent portions of the catheter
11, i.e., the plugs 81 and 83 and the partition 55. The
thin layer 67 on the projecting portion of the thermistor
45 is many times thinner than the mounting body 71. The
thermistor 45 should be a fast response thermistor when
30 mounted and preferably has a response time which is rapid
enough to measure the temperature changes within the
interval between heart beats. For example, an average
mounted response time of 100 to 150 milliseconds or less
should be adequate.
In use of the catheter ll, the catheter tube 13
is introduced through a vein or artery of a patient and
into the heart (Fig. 7~ using known techniques. The
balloon 41 is inflated through the balloon inflation lumen
5 15 and the port 40, and the inflated balloon is used to
carry the distal end 39 of the catheter ll to the desired
location. In the example shown in Fig. 7, the balloon 41
is carried into the pulmonary artery 87. Because the
thermistor 45 is below the body line 79, it will not rub
lO against any introducer which is used, either d~ring the
insertion or withdrawal of the catheter tube 13. The
location of the catheter tube 13 within the heart will
depend upon the procedure to be carried out.
For example, to calculate ejection fraction, the
7 15 catheter tube is inserted into the heart so as to place the
injectate port 47 into the right atrium 89, the thermistor
45 into the pulmonary artery 87 and the distal port 43 into
the pulmonary artery 87 as shown in Fig. 7. A bolus of
cold fluid is then injected into the right atrium 89
20 through the injectate port 47 and allowed to mix with the
bloodstream in the right ventricle 91. The blood and cold
fluid mixture flow along the catheter tube 13 and over the
thermistor 45 in the pulmonary artery 87. The temperature
of the mixture changes with each heart beat, and the
25 thermistor 45 can track each temperature change so as to
provide a stepped temperature chart. This information can
then be processed in accordance with known techniques to
provide ejection fraction. Pressure can be monitored, if
desired, through the through lumen 17.
Although an exemplary embodiment of the invention
has been shown and described, many changes, modifications
and substitutions may be made by one having ordinary skill
in the art without necessarily departing from the spirit
and scope of this invention.
