fig1 is a perspective view of the multi - purpose , multi - parameter catheter 10 of the present invention . the main body 12 of the catheter 10 is an extended section of polyvinyl chloride ( pvc ) tubing . in the catheter 10 of the preferred embodiment , tubing 12 , as shown in fig2 is a complex multi - lumen tubing having a central lumen 13 defined by an interior pvc core 14 which is connected to a peripheral wall 16 of the tubing 12 by support ribs 17 . spaces between support ribs 17 , the interior core 14 and the peripheral wall 16 define a series of interior longitudinal lumens in the catheter tubing 12 . for example , in fig2 can be seen optics , kevlar and thermistor lumen 18 , balloon lumen 20 , distal thermal element pressure port lumen 22 , thermal element connector lumen 23 and a proximal lumen 24 . central or distal lumen 13 , the optics lumen 18 , the balloon lumen 20 , the distal thermal element pressure port lumen 22 , the thermal element connector lumen 23 and the proximal lumen 24 are generally parallel and coextensive for the entire working length of the catheter main body tubing 12 , which in the preferred embodiment is 110 centimeters . interposed between the catheter tubing 12 and catheter interconnects ( discussed below ) at the proximal end of the catheter 10 is a manifold 26 which will be described in greater detail below . at the proximal end 27 of the catheter 10 is provided a series of interconnects between the catheter lumens , with the interface between said interconnects and the catheter lumens being provided in the manifold 26 . as seen in the upper right hand corner of fig1 the first of the interconnects noted above is a fiber optic coupler 28 . the coupler body 30 is a molded plastic body which plugs into an optical module associated with a svo 2 monitor ( not shown ). at the proximal end of the coupler 28 are a pair of plug - in members 32 which receive fiber optic filaments 33 ( also see fig4 ). included with the fiber optic filaments 33 are a series of elongated kevlar elements 34 ( fig2 ) which support and protect the fiber optic filaments 33 in the connector 28 , in connecting tubing 36 connected between the fiber optic coupler 28 and a secondary manifold 37 which is connected to a stop cock body 38 at a proximal end thereof with tubing 40 extending from the distal end of the stop cock body 38 and into the manifold 26 at its proximal end . similarly , a thermistor connector 42 includes a pair of thermistor wires 43 ( fig2 ) which extend through tubing 44 connected at the thermistor connector 42 by molded fitting 46 and are received into the secondary manifold 37 and stopcock 38 to be received into the tubing 40 connected to the manifold 26 . next are a series of luer lock fittings 47 , with each fitting 47 and its associated tubing 48 interfacing with a corresponding lumen of the catheter tubing 12 at the manifold 26 . for convenience in use , in the preferred embodiment of the present invention the tubing 48 is color coded . luer lock fitting 47a is connected to tubing section 48a , and tubing 48a is connected at its distal end to the pulmonary artery distal lumen 13 in the manifold 26 . next , the cvp luer lock 47b is connected to tubing section 48b which is in turn connected at its distal end to the proximal lumen 24 in the manifold 26 . next , luer lock fitting 47c is connected at its proximal end to tubing section 48c which is in turn connected at its distal end to the distal thermal element pressure port lumen 22 in the manifold 26 . thermal element plug 50 comprises a plastic body 51 having a cylindrical disc 52 joined thereto at a mid portion of the plug . the disc 52 is a peripheral flange which extends beyond the body 51 of the plug 50 . mounted in the disc 52 are a plurality of metal pins 53 ( fig5 ) which extend through the plug 50 to protrude at an opposite end thereof . connected to the lower end of the pins 53 are thermal element connectors or wires 54 which connect to the pins 53 that protrude from the back of the disc 52 to be received into extension tubing 56 which is connected between the thermal plug 50 and the manifold 26 . connected to the upper ends of the pins 53 is a temperature control apparatus such as described and claimed in u . s . pat . no . 5 , 277 , 191 entitled &# 34 ; heated catheter for monitoring cardiac output &# 34 ; issued jan . 11 , 1994 and assigned to the assignee of the present invention , which is herein incorporated by reference to provide a better understanding of the present invention . the thermal element connectors can be wire connectors 54 as in the preferred embodiment of fig1 or could be replaced by coils carrying temperature regulated fluid therein as described in greater detail below . the thermal element connectors 54 continue through the manifold 26 into the thermal element connector lumen 23 to extend along the working length of the catheter tubing 12 to a thermal element 55 , disposed near the distal end of the catheter 10 . stop cock 57 which includes stop cock valve 58 , stop cock sleeve 59 and extension tubing 60 interfaces with the balloon lumen 20 at the manifold 26 . in fig6 the manifold 26 is shown partly in section . not all lumen / tubing interfaces in the manifold 26 are shown in fig6 but sufficient detail is provided in fig6 to give an understanding of the construction within the interior of the manifold 26 . within the manifold 26 , each extension tube is aligned and abutted with its respective lumen of the catheter 10 at the interface thereof , the manifold 26 fixing the position of the main body tubing 12 of the catheter 10 with respect to the extension tubing . although only the tubing 40 connected to the optics lumen 18 is shown in section in fig4 the drawing is illustrative to depict the manifold interface for each catheter lumen and its respective extension tubing section . fig2 and 3 can now be reexamined to understand the interior workings of the catheter 10 . for example , note in fig2 that the optics , kevlar and thermistor lumen 18 includes not only optical fiber filaments 33 but also the supporting kevlar filaments 34 , as well as thermistor wires 43 . opposite lumen 18 is the thermal element lumen 23 which receives therein thermal element connectors 54 . note that fig3 is taken looking toward the distal end of the catheter 10 and is taken about 25 centimeters from that distal end . although the 110 centimeter length of the catheter tubing 12 is referred to as the working length , for about 85 centimeters the main body tubing 12 is essentially smooth . in the 25 centimeters of main body tubing 12 beginning at the distal end and moving forward are located many of the apparatus associated with the detection of blood - related parameters through the use of the catheter 10 . about twenty - five centimeters from the distal end of the catheter 10 is located a proximal notch 64 ( fig7 ) provided in the proximal lumen 24 . as can be seen from the enlarged view of fig7 the proximal lumen 24 is plugged by a solid pvc plug 66 to direct the flow of injectate into the blood stream rather than permitting it to advance in the proximal lumen 24 beyond the proximal notch 64 . about one centimeter from the proximal notch 64 , the thermal element connectors 54 emerge from the thermal element connector lumen 23 at a notch 67 ( fig7 a ). in the preferred embodiment of the present invention connector wires 54 emerge from the lumen 23 at notch 67 to connect with bifilar wires 55a and 55b which are thereafter circumferentially wound about the catheter main body 12 at a reduced diameter section 68 to form a thermal element 55 about 10 centimeters long . such reduced diameter section 68 is also depicted in fig3 . note in the reduced diameter portion 68 of catheter 10 shown in fig3 that although the diameter of the tubing 68 is reduced from diameter d 1 to diameter d 2 , and that all lumens , including the optics , kevlar and thermistor lumen 18 &# 39 ;, the balloon lumen 20 &# 39 ;, the distal thermal element pressure port lumen 22 &# 39 ;, the thermal element connector lumen 23 &# 39 ; and the proximal lumen 24 &# 39 ; are reduced in size , such lumens remain sufficiently large to receive and support the fiber optic filaments 33 , the kevlar filaments 34 and the thermistor wires 43 in reduced diameter section lumen 18 &# 39 ; and the thermal element connectors 54 in reduced diameter section lumen 23 &# 39 ;. although the preferred embodiment of the present invention discloses a multi - lumen multi - purpose catheter having a reduced - diameter portion of the catheter body for receiving a thermal element , it is believed that the incorporation of a reduced - diameter portion in the catheter body is not essential to the practice of the present invention . for example , thermal element 55 could be mounted at the distal end of a fiber optic catheter having a catheter body of uniform cross - section at a location comparable to the reduced - diameter portion 68 and continue to provide many of the advantages ascribed to the multi - lumen , multi - purpose catheter of the preferred embodiment of the present invention . in the preferred embodiment , the opening 67 is potted to cover the connection of wires 54 and 55 . the bifilar wires 55a and 55b have a soft copper composition and are circumferentially wound about the reduced diameter portion 68 of the catheter body 12 for about 10 centimeters and terminates at a second notch 70 in the heater wire lumen 23 . the terminus of the thermal element 55a , 55b wires is best seen in fig8 in which the wires 55a , 55b are soldered to a solid pc rod 72 . fig7 and 8 also show the pitch or spacing of the wires 55a and 55b to be 0 . 017 &# 34 ; center to center . the notch 70 is also potted to enclose the wires 54 with a polyurethane coating 73 . as can also be seen in fig1 and 7 , a polyurethane coating 74 overlies the wires 55a , 55b for the entire length of the thermal element 55 . alternative embodiments of the thermal element 55 are shown in fig8 a through 8g . in fig8 a , a second embodiment of the thermal element 55 comprises thin film member 56a , which is spiral wound about the reduced - diameter section 68 of the catheter body 12 . in fig8 b , a third embodiment of the thermal element 55 comprises thin film sleeve 56b , incorporating a coiled conductive element 57b embedded therein in the coiled pattern shown , which overlies the reduced - diameter portion 68 of the catheter body 12 . the relationship between the sleeve 56b and the catheter body 12 at reduced - diameter portion 68 is better seen in the enlarged cross - sectional view of fig8 c . in fig8 d , a fourth embodiment of the thermal element 55 comprises a self - regulating conductive plastic sleeve 55d , incorporating power wires 57d , on opposite sides thereof as shown in fig8 e , mounted on the reduced - diameter section 68 of the catheter body 12 . in fig8 f and 8g , a fifth embodiment of the thermal element 55 comprises a heat exchanger 55f , having an interior fluid - filled jacket 56f , an exterior sheath 57f , and coils ( not shown ) comparable to connectors 54 associated therewith , to transfer thermally regulated fluids from an external heat exchanger ( not shown ) to heat exchanger 55f . in each instance , each thermal element 55a / 55b , 56b , 56d and 55f is connected to an appropriate thermal regulator or heater exchanger ( not shown ) by thermal wires or coils 54 extending from the thermal element 55 to an appropriate connector , comparable to thermal plug 51 , disposed at the proximal end of the catheter 10 . about one centimeter from the distal end of the thermal element 55 is a distal thermal pressure port 76 ( fig1 ). the distal thermal pressure port 76 is very similar to the proximal notch 64 and the structural details of the proximal notch 64 as shown in fig7 apply equally to the pressure port 76 . about 7 centimeters from the pressure port 76 is the distal end 77 of thermistor 42 . distal end 77 of thermistor 42 is exposed to the blood stream and senses the temperature therein . now refer to the distal end of the catheter body 12 in both fig1 and 9 . as better seen in fig9 the distal end of the catheter body 12 shows a balloon 78 secured to the catheter body 12 at opposite ends 78a and 78b by adhesive 80 . the balloon 78 is attached to the periphery of the catheter body 12 and is inflated through the balloon lumen 20 at an opening 81 which opens into the balloon lumen 20 at the distal end of the catheter 10 . the balloon 78 is inflated by a means well known in the art . the distal end of the catheter as seen in fig1 includes an open port 79 which is the exit port 79 for the distal lumen 13 and a closed port 80 which is the distal port 80 for the optics , kevlar and transistor lumen 18 . exposed at the distal end 82 of the catheter body 12 are the ends 83 of optical fibers 33 . fig1 shows the thermal plug 50 of the present invention incorporating the circuit 84 ( fig1 ). in fig1 , some of the elements of the circuit 84 shown in fig1 are physically shown rather than schematically shown . for example , pins 1 - 6 are shown . a resistor ( rp ) 85 and an adjusting resistor ( ra ) 86 are shown , as well as a jumper 89 ( connecting wires 92 and 93 ) and a jumper 90 ( connecting leads 97 and 98 ). the wiring shown in fig1 allows two four - wire resistance measurements to be made while using only five wires in the cable connections of the thermal plug 50 at the interface of the thermal element 55 and the cco instrument described in above - referenced u . s . pat . no . 5 , 277 , 191 . the principle that enables the use of five wires rather than eight is shown in fig1 and fig1 . in fig1 current i is generated by a current source which can be either ac or dc . at an ammeter &# 34 ; a &# 34 ; the current through the thermal element 94 is measured . to measure the voltage drop across the thermal element 94 independently of the connector wire and connector contact resistance , the voltage is measured at a voltmeter &# 34 ; v &# 34 ; through resistor ( rp ) 85 and the adjusting resistor ( ra ) 86 . the resistance of the voltmeter is much higher than the combined parallel resistance of rp 85 and ra 86 , therefore , the voltage measurement across the thermal element 94 is not materially affected by the resistances at rp 85 and ra 86 , or by cable wire and connector contact resistance 119 . in fig1 current i ref is generated by a current source which can be either ac or dc . at an ammeter &# 34 ; a &# 34 ; the current through the reference resistance , which rp 85 and ra 86 in parallel is measured . to measure the voltage drop across the reference resistance independently of the connector wire and connector contact resistance , the voltage v ref is measured at a voltmeter &# 34 ; v &# 34 ; through thermal element 94 . the resistance of the voltmeter is much higher than the thermal element resistance , therefore , the voltage measurement across the reference resistance is not materially affected by the thermal element or by cable wire and connector contact resistance 119 . from the voltage measurement and current measurement shown in fig1 , the temperature at the thermal element can be calculated . the first step is equation ( 1 ) in which the resistance at the thermal element is calculated from ohm &# 39 ; s law as the quotient of the voltage divided by the current : ## equ1 ## the temperature at the thermal element is then calculated in equation ( 2 ) as follows : ## equ2 ## where a = temperature coefficient of resistance , calibration of the thermal element resistance as measured at a reference temperature is implemented by the resistor 85 ( rp ) and adjusting resistor ( ra ) 86 connected in parallel . the thermal element resistance in each catheter is measured in a reference temperature bath during manufacture and the adjusting resistor ( ra ) is selected to yield the reference resistor r ref when connected in parallel with the resistor rp . this reference along with the temperature coefficient of resistance ( a ) for the thermal element 94 is used in converting thermal element resistance data into temperature data . the reference resistance r ref is calculated from measurements of voltage ( v ref ) and applied current ( i ref ) as shown in fig1 where : ## equ3 ## as shown in the wiring diagram of fig1 , leads 91 , 93 , 92 and 97 are connected to the thermal plug 50 at pins 5 , 4 , 3 and 1 respectively . thermal element resistance is measured by applying a known current as measured across pins 5 and 4 to leads 91 and 93 while measuring the voltage drop across leads 92 and 97 between pins 1 and 3 . because of the high resistance of the voltmeter taking this measurement and the low resistance across the resistor 85 and adjusting resistor 86 in series with the voltmeter lead 97 the accuracy of this voltage measurement is not degraded , and an additional wire or sensing lead not including such resistance is not required . similarly , the resistance across the calibration resistor , which is the combination of rp and ra in parallel , can be measured by applying a known current across pins 5 and 6 through leads 91 and 98 and measuring the voltage across the calibration resistor through a voltmeter placed across pins 1 and 3 and leads 97 and 92 . thus pin 2 becomes a spare pin location , with no pin physically placed at that location for the application of the present invention . to calculate thermal element temperature , a known current is applied to the thermal element 94 from pins 4 and 5 via leads 93 and 91 from the thermal plug 50 . the resulting voltage drop is measured across pins 1 and 3 via leads 97 and 92 . then using equations ( 1 ) and ( 2 ), the temperature of the thermal element 94 is calculated . an alternate thermal plug 101 and instrument cable socket 102 are shown schematically in fig1 . socket springs 104 and 106 provide two independent connections ( lead wires ) to opposite sides of a plug pin 108 . socket springs 110 and 112 make two independent staggered connections ( lead wires ) to a plug pin 114 . the springs 110 , 112 may be on opposite or the same side of the plug pin 114 . socket springs 115 and 116 may make separate connections ( lead wires ) to plug pin 118 as shown or may be replaced by a single spring connector in socket 102 . by design , the catheter 10 of the present invention incorporates thermal element 55 at a reduced diameter portion of the catheter body 12 coil for use in the measurement of continuous cardiac output measurement , such measurement taken in conjunction with the thermistor 77 located distally of the thermal element 55 . for a complete description of the use of such thermal element in an application for measurement of continuous cardiac output , please refer to above - referenced u . s . pat . no . 5 , 277 , 191 . the incorporation of the thermal element 55 into the catheter body 12 for the measurement of continuous cardiac output is achieved with no loss in the capability of the catheter to provide a measurement of oxygen concentration or svo 2 in the blood through the use of fiber optics as described in u . s . pat . no . 4 , 453 , 218 entitled &# 34 ; signal filter method and apparatus &# 34 ; and assigned to the assignee of the present invention . such dual capacity is permitted by the provision of a reduced diameter body portion of the catheter body 12 which reduces not only the diameter of the catheter body at such body portion but also reduces the size of the lumens in which the optics , as well as the heater wires are located . however , such reduction in lumen size is not adverse to fiber optic performance as it relates to measurement of svo 2 or to thermistor performance as it relates to the measurement of temperature . further , the reduced diameter portion of the catheter 10 has no impact on the efficacy of the thermal element connectors 54 used in the thermal element 55 . nor does the reduced diameter catheter body portion have any effect on the flow of injectates through the flow ports or the removal of samples through those ports . simply stated , the reduced diameter portion 68 of the catheter body 12 has no impact on the measurements to be taken by the catheter 10 in connection with the evaluation of separate blood - related parameters associated with oxygen saturation , continuous cardiac output and thermal dilution values . by mounting the thermal element 55 at the reduced diameter portion 68 the catheter 10 is useable for continuous cardiac output measurements and has a symmetric diameter for its entire working length . an alternative construction , such as a catheter body of a single diameter throughout its working length , which then wound a heater coil about the distal end thereof would produce a discontinuity in such catheter and such discontinuity could be noticeable in the insertion and removal of such catheter . the multi - purpose , multi - parameter cardiac catheter of the present invention incorporates the heater coil at a reduced diameter section thereof at the distal end of the catheter and yet generally maintains a single diameter throughout the working length of the catheter , because the addition of heater coil and coating at the reduced diameter portion creates an overall diameter at that portion that is consistent with the diameter at the remainder of the working length of the catheter . consistency of diametric proportions throughout the working length of the catheter should facilitate insertion and removal of the catheter of the preferred embodiment of the present invention . having described a preferred embodiment of the present invention , it is not the intention to thereby limit the scope of the invention to the description set forth , but rather to define the invention in terms of the claims which follow .
a multi - lumen , multi - purpose cardiac catheter which incorporates optical filaments and an optical coupler for use with external apparatus for determining the oxygen concentration in the blood of a patient under critical care conditions , as well as incorporating therein a thermal element useable with a second external apparatus for measurement of continuous cardiac output . a thermal plug provides an interface between a temperature control apparatus and the thermal element to simply and accurately monitor and control the temperature of the thermal element . a temperature monitoring circuit in the thermal plug facilitates temperature measurement at the thermal element . the catheter also includes a thermistor and at least one injectate port for enabling the user to also conduct thermal dilution readings and obtain intermittent measurements of cardiac output . the combination of a thermal dilution catheter with a sv0 2 catheter and a continuous cardiac output catheter gives the multi - purpose catheter above described substantial versatility as well as providing the user with a versatile cardiac catheter device which enables him to conduct multiple evaluations of disparate blood - related parameters which require the use of separate apparatus . simply by switching from one external apparatus to the other , the user can obtain readings for different blood - related parameters useful in the treatment of the cardiac patient .