DUAL-DIAMETER MULTIFUNCTION CATHETER
This is a continuation of the prior application Ser. No. 07/494,109 filed Mar. 15, 1990, the benefit of the 5 filing date of which is hereby claimed under 35 U.S.C. § 120 now U.S. Pat. No. 5,108,369.
FIELD OF THE INVENTION
This invention relates generally to catheters and, 10 more particularly, to catheters having a dual-diameter construction.
BACKGROUND OF THE INVENTION
Catheters have long been used in the medical field to 15 invasively obtain patient information and administer treatment. A conventional catheter is an elongate tube having a distal end and a proximal end. The distal end is designed for insertion into a fluid-filled passageway or cavity in the patient, such as one of the various intravas- 20 cular conduits. The proximal end of the catheter remains outside of the patient and is provided with a termination assembly accessible to the health care provider. In this manner, the catheter provides a communication link between the patient's fluid-filled passageway 25 or cavity and the health care provider for diagnosis and treatment.
Typically, the catheter includes one or more axial conduits known as lumens extending between the distal and proximal ends of the catheter. These lumens may 30 contain, for example, electrical wires or optical fibers that transmit information between sensors located at the distal end of the catheter and bedside instruments at the proximal end of the catheter. The operation of the sensors is controlled and their outputs interpreted by the 35 bedside instruments, allowing the sensor/catheter/instrument system to be used for monitoring and diagnosis.
Other lumens may extend between the termination assembly and ports provided at various points along the 40 ing through the conduit in which the transducer-carry
assembly by yet another lumen in the catheter. The balloon can, thus, be controllably inflated by the health care provider and used as a flotation device to facilitate positioning of the catheter in the pulmonary artery.
The thermal dilution method does, however, have certain disadvantages. For example, this technique has proved to be of limited accuracy. In addition, cumbersome apparatus are required to provide the bolus and only intermittent information can be obtained.
Another approach to the measurement of cardiac output involves the use of ultrasonic energy. Unlike the thermal dilution method discussed above, ultrasonic techniques can provide cardiac output measurements continuously. This is of considerable value in the treatment of critically ill patients whose cardiac functions may change abruptly.
Ultrasonic techniques involve the use of a transducer positioned close to the distal end of the catheter. This transducer is connected to the termination assembly at the proximal end of the catheter by electrical wires threaded through one of the catheter lumens. A bedside monitor attached to the termination assembly applies a high-frequency electrical signal (typically in the megaHertz range) to the transducer, causing it to emit ultrasonic energy. Some of the emitted ultrasonic energy is then reflected by the blood cells flowing past the catheter and returned to the transducer. This reflected and returned energy is shifted in frequency in accordance with the Doppler phenomenon.
The transducer converts the Doppler-shifted, returned ultrasonic energy to an output electrical signal. This output electrical signal is then received by the bedside monitor via the lumen wiring and is used to quantitatively detect the amplitude and frequencyshifted Doppler signal associated with the ultrasonic energy reflected from the moving blood cells.
Existing ultrasonic measurement systems process the amplitude and frequency shift information electronically to estimate the average velocity of the blood flow
catheter, placing the termination assembly of the catheter in fluid communication with those ports. As a result, characteristics of fluids in the patient passageway can be monitored and additional therapeutic fluids can be introduced by the health car provider.
One application in which catheters have been extensively used is the determination of volumetric flow rate in an intravascular conduit. In that regard, several catheter-based techniques have been developed to determine a patient's cardiac output, i.e., the volumetric flow rate of blood in the patient's pulmonary artery.
The first of these approaches is conventionally termed the "thermal dilution" method. Under this approach, a bolus of cold solution is introduced into one of several lumens in a multiple-lumen catheter, via the 55 termination assembly. The cold solution then enters the intravascular conduit through a port at the end of the lumen and on the exterior of the catheter. A thermistor located on the distal, downstream end of the catheter is coupled to the termination assembly by wires positioned in another lumen. The "dilution" of, or change in, blood temperature at the thermistor with time is then measured by an instrument coupled to the termination assembly. The resultant thermal change is electronically interpreted and cardiac output computed therefrom.
Thermal dilution techniques also typically employ an inflatable segment or balloon at the distal end of the catheter. This balloon is coupled to the termination
ing catheter is inserted. Such systems also require that an independent estimation of the cross-sectional area of the conduit be made using one of a variety of techniques taught in the literature, including, for example, the approach disclosed in U.S. Pat. No. 4,802,490. Cardiac output is then computed by multiplying the average velocity and cross-sectional area estimates.
One particular method of generating and processing ultrasonic signals for use in cardiac output determination employs a cylindrical transducer. The transducer is mounted coaxially on a catheter suitable for insertion into the pulmonary artery. As will be appreciated, there is, thus, a need for a catheter capable of carrying a cylindrical ultrasound transducer. Furthermore, in order to enhance the clinical utility of such a catheter, the catheter should retain some or all of the clinical functions already available through nonultrasonic catheters. Such a multifunction catheter would, however, be subject to a variety of design constraints.
Specifically, the catheter must have a small diameter for insertion into the particular conduit of interest and to minimize trauma to the patient at both the point of entry and along the inside region of the conduit in which it is inserted. Furthermore, the catheter should be designed so that the transducer does not significantly alter the catheter's diameter, thereby minimizing flow occlusion, thrombus formation and other mechanical traumas.
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The catheter should also have a high lumen count, in other words, a relatively large number of independent lumens, so that several types of information can be collected and a variety of treatments performed. In addition, the lumens should have relatively large cross 5 sections, especially when they are employed to measure pressures via a fluid connection between the distal and proximal ends of the catheter. The construction of a catheter having a small diameter, however, is in direct conflict with the provision of a high lumen count and 10 large lumen crosssection.
The flexibility of the catheter should also be designed to provide an optimal balance between the catheter's maneuverability through tortuous passageways and its tendency to kink and fold. Furthermore, it is essential 15 that the flexibility be uniform over the length of the catheter to further reduce the probability of kinking due to the forces applied on flexible sections of the catheter by other, relatively inflexible, sections during insertion.
Finally, because catheters are used invasively, they 20 are conventionally disposed of after a single use. Thus, it is desirable to keep the catheter's unit cost as low as possible. For that reason, the construction of the catheter should be simple and involve a minimum expense. Further, the electrical and mechanical coupling of a 25 transducer to the catheter should be straightforward.
In view of the preceding remarks, it would be desirable to provide a small-diameter multifunction catheter that is capable of carrying a coaxially mounted ultrasound transducer that has a high lumen count and large 30 lumen cross-sectional area, and that is uniformly flexible and easy to construct.
SUMMARY OF THE INVENTION
In accordance with this invention, a catheter is pro- 33 vided including an external tube and an internal tube. The external tube has proximal and distal ends and is provided with a primary lumen and a plurality of secondary lumens. The primary lumen is roughly circular in cross section and each of the secondary lumens 40 roughly defines a segment of an annul us in cross section. The internal tube also has proximal and distal ends and is provided with a plurality of inner tube lumens. Each inner tube lumen roughly defines a circular sector in cross section. The internal tube is receivable within the 45 primary lumen of the external tube.
In accordance with another aspect of this invention, the catheter includes an ultrasound transducer attached adjacent the distal end of the external tube. A coaxial cable, receivable within one of the secondary lumens, is SO connectable to the ultrasound transducer. The internal tube is further made of a first material having a hardness of Shore D6S and the external tube is made of a second material having a hardness of Shore A93. Thus, the internal tube is relatively rigid and the external tube is 55 relatively flexible.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will presently be described in greater detail, by way of example, with reference to the accom- 60 panying drawings, wherein:
FIG. 1 is an isometric view of a catheter constructed in accordance with this invention;
FIG. 2 is an isometric view of a number of segments of the catheter of FIG. 1; 65
FIGS. 3A and 3B are sectional views of the catheter of FIGS. 1 and 2 along the section lines A—A' and B—B' of FIG. 2;
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FIG. 4 is a sectional view of a segment of the catheter illustrating the connection of a transducer thereto;
FIG. 5 is an exploded isometric view of a connector shown in FIG. 4;
FIG. 6 is a sectional view of the connector of FIG. 5; and
FIG. 7 is a block diagram illustrating a control and processing system used with the catheter of FIG. 1.
DETAILED DESCRIPTION OF THE
PREFERRED EMBODIMENT
Referring now to FIG. 1, a catheter 10 constructed in accordance with this invention is shown. As will be described in greater detail below, catheter 10 is easy to use, durable, simply constructed, and able to perform a variety of functions. In that regard, the embodiment of the catheter shown is designed for intravascular use to infuse therapeutic fluids, extract blood samples, provide electrical or optical communications between ends of the catheter, determine blood pressure, and determine cardiac output by Doppler ultrasound techniques.
As shown in FIG. 1, the catheter 10 includes an internal tube 12, external tube 14, ultrasound transducer 16, sensor 18, and termination assembly 20. The internal tube 12 and external tube 14 collectively define a catheter body that supports the other components and allows them to be positioned at desired locations within an intravascular conduit of a patient. The transducer 16 and sensor 18 obtain information from the patient for use in diagnosis and treatment, as will be described in greater detail below. The termination assembly 20 is coupled to both the internal tube 12 and external tube 14, and provides an interface between the catheter 10 and a control and processing system 22.
Addressing the various components of catheter 10 individually, the internal tube 12 is an elongate piece of flexible tubing having defined therein three lumens 26, 28, and 30. Tube 12 is preferably made of a standard medical grade flexible polyurethane having a hardness of Shore D6S and is roughly 1 IS centimeters long and 0.117 centimeter in diameter.
Lumens 26, 28, and 30 extend to the proximal end 32 of internal tube 12 and terminate at the termination assembly 20. Lumen 26 is known as a distal pressure lumen and extends from assembly 20, through the entire length of tube 12, to a distal pressure port 34.
Lumen 28 is known as a balloon lumen and extends from assembly 20 through the length of tube 12. Lumen 28 opens to the exterior of tube 12 at a balloon port 36 approximately five millimeters from the distal end 38 of tube 12. Finally, lumen 30 is known as a sensor lumen and also extends from assembly 20 through the length of tube 12. Lumen 30 opens to the exterior of tube 12 at a sensor port 40 about forty millimeters from the distal end 38 of tube 12.
As shown in FIGS. 3A and 3B, lumens 26, 28, and 30 each define a circular sector when viewed in cross section. The distal pressure lumen 26 has the largest crosssectional area (roughly 0.5 square millimeter). In contrast, the balloon and sensor lumens 28 and 30 are smaller in cross-sectional area (roughly 0.3 square millimeter each), but adequate for the assigned functions. The lumens 26, 28, and 30 are defined by walls of tube 12 that are of uniform thickness (roughly 0.125 millimeter).
From the foregoing, it is clear that tube 12 is provided with a relatively large number of usable lumens. Furthermore, when compared to conventional lumens of
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circular cross section provided in a catheter of the same diameter, each lumen 26, 28, and 30 has a relatively large cross-sectional area. For example, the distal pressure lumen 26 has a cross-sectional area comparable to that of the distal pressure lumen of a conventional eight French (2.67 millimeters in diameter) thennodilution catheter, despite the fact that the diameter of tube 12 is smaller (0.117 centimeter). This is an important advantage since it allows lumens having suitable pressure measurement characteristics to be included in a catheter having a diameter that is smaller than standard eight French devices.
The external tube 14 is an elongate piece of tubing and has five lumens 46, 48, 50, 52, and 54 provided therein. Tube 14, like tube 12, is made of a medical grade polyurethane, but has a hardness of Shore A93, making it relatively more flexible than the internal tube 12. The external tube 14 is roughly 105 centimeters long and 0.264 centimeter in diameter.
Addressing the various lumens 46, 48, 50, 52, and 54 20 individually, the center lumen 46 extends between the proximal end 56 and distal end 58 of tube 14 and is designed to receive the internal tube 12. Thus, as shown in FIG. 3A, the internal lumen 46 has a circular cross section and is slightly greater in diameter (roughly 0.122 centimeter) than the outer diameter of the internal tube 12. As shown in FIG. 1, internal tube 12 is longer than external tube 14 and extends from the distal end of internal lumen 46 by roughly 10 centimeters.
Lumens 48 and 50 are known as the first and second proximal pressure lumens, respectively. These lumens 48 and 50 begin at the termination assembly 20 at the proximal end 56 of tube 14. The first proximal pressure lumen 48 then extends the length of tube 14 and opens to the tube's exterior at a first proximal pressure port 60 35 located approximately five millimeters from the distal end 58 of tube 14. The second proximal pressure lumen 50 also extends the length of tube 14 and is open to the exterior of tube 14 at a second proximal pressure port 62 located roughly 180 millimeters from the distal end 58 40 of tube 14.
Lumens 52 and 54 are known as the injection and transducer lead lumens, respectively. These lumens 52 and 54 begin at the proximal end 56 of tube 14 at the termination assembly 20. The injection lumen 52 then 45 extends the length of tube 14 and is open to the exterior of tube 14 at an injection port 64 located roughly 150 millimeters from the distal end 58 of tube 14. The transducer lead lumen 54 similarly extends the length of tube 14 and is open to the tube's exterior at a transducer lead port 66 located at the distal end 58 of tube 14.
As shown in FIG. 3A, lumens 48, 50, 52, and 54 each define a segment of an annulus in cross section. In that regard, the cross-sectional area of lumens 48,50, and 52 is roughly 0.275 square millimeter each, while the crosssectional area of lumen 54 is roughly 0.467 square millimeter to accommodate the transducer wiring. Lumens 48, 50, and 52 are spaced between the inner and outer surfaces of tube 14. Lumen 54 is also evenly spaced between the inner and outer surfaces of tube 14 but is approximately twice as large in cross section. As will be appreciated from FIG. 3A, with the internal tube 12 inserted in external tube 14, the size and location of the various lumens result in a substantially uniform wall thickness for lumens 48, 50, and 52.
Addressing now the transducer 16, transducer 16 may be any one of a variety of suitable transducer types, but is preferably of a cylindrical construction. The
transducer 16 is located at the intersection of the internal tube 12 and the external tube 14 where it can be easily attached to tube 14 and the transducer wiring by a connector 70. As will be appreciated, the internal tube 12 can be positioned inside the external tube 14 before or after transducer 16 is attached without interference.
Turning now to a more detailed discussion of the construction of connector 70, reference is had to FIGS. 4, 5, and 6. As shown, the connector 70 includes three components: a plastic collar 72 and a pair of flexible conductive ring clips 74 and 76. The plastic collar 72 includes a cylindrical wall 78 coupled to a circular base 80. As shown in FIG. 5, the diameter of collar 72 is roughly equal to the diameter of transducer 16 and external tube 14.
The two coaxially aligned roughly cylindrical ring clips 74 and 76 have enlarged rims 82 that are molded into the circular base 80 of collar 72. As shown, the ring clips 74 and 76 are spaced apart at the collar 72 by a distance corresponding to the thickness t of the cylindrical transducer 16, but are slightly closer together at their projecting ends. Each ring clip 74 and 76 is interrupted by a plurality of circumferentially spaced-apart slots 84, to define a plurality of fingers 86, adding flexibility to the ring clips 74 and 76.
Because the projecting ends of the ring clips 74 and 76 are normally spaced apart by a distance less than the cylindrical main element thickness t, when an end of the transducer 16 is inserted between ring clips 74 and 76, they spread apart and apply a slight force to the cylindrical transducer 16 to maintain the desired electrical and mechanical interface. To further ensure this connection, some type of detent may also be used. As will be appreciated, a connector 70 constructed in this manner allows the desired mechanical and electrical connection to be easily and securely made to the transducer 16. Thus, the transducer 16 can be quickly removed and replaced as needed.
Addressing now the coupling of the two ring clips 74 and 76 of connector 70 to the transducer wiring 88, because a single cylindrical element 16 is employed, a coaxial cable provided in lumen 54 can be conveniently used for transducer wiring. More particularly, the internal conductor of cable 88 is coupled to the internal ring clip 76 of connector 70 by solder or a conductive adhesive and, thus, is coupled to the internal surface of transducer 16. Similarly, the external conductor of cable 88, commonly known as the grounding shield, is coupled to the external ring clip 74 of connector 70 by solder or a conductive adhesive and, thus, is coupled to an external surface of transducer 16. The use of coaxial cable 88 instead of conventional wires significantly enhances the overall flexibility of catheter 10.
The sensor 18 may be any one of a variety of devices including, for example, a thermistor or fiber-optic cell. Sensor 18 is preferably positioned adjacent the sensor port 40 on the internal tube 12. Sensor 18 is coupled to the termination assembly 20 by electrical wires or an optical fiber 90 located in lumen 30.
Turning now to a discussion of termination assembly 20, assembly 20 allows the various components of control and processing system 22 to be coupled to the catheter 10. The termination assembly 20 includes a plurality of flexible tubings 92, 94, 96, 98, and 100 coupled to the distal pressure lumen 26, balloon lumen 28, first proximal pressure lumen 48, second proximal pressure lumen 50, and injection lumen 52. The tubings 92, 94, 96, 98, and 100, respectively, end in a distal pressure
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