I : i `. g 1 1. ,1,
Contents
1. 5 720 293 Sheet 2 of 3 Feb 24 1998 U S Patent Ad LP HOLS IW FHL LNO NI V LVG o 70 07 i 7 7 43013 o GNI IN Col Off 5 720 293 Sheet 3 of 3 Feb 24 1998 U S Patent 5 720 293 1 DIAGNOSTIC CATHETER WITH MEMORY CROSS REFERENCE TO RELATED APPLICATIONS This patent application is a continuation in part applica tion of U S patent application Ser No 07 769 536 to Quinn et al filed Oct 1 1991 now abandoned which was originally a continuation in part application of U S patent application Ser No 07 647 578 to Quinn et al filed Jan 29 1991 now abandoned This patent application is also a continuation in part application of U S patent application Ser No 08 049 321 to Quinn et al filed Apr 19 1993 which is a continuation application of U S patent applica tion Ser No 07 647 578 to Quinn et al filed Jan 29 1991 now abandoned and which is hereby incorporated by ref erence as is if fully set forth herein BACKGROUND OF THE INVENTION 1 Field of the Invention The present invention relates to a diagnostic catheter for insertion into the bloodstream of a patient and more particularly to a diagnostic catheter with an integral memory device which contains factory calibration and factory iden tification information software program segments patient specific calibration2. 47 The thermodilution catheter assembly of claim 46 wherein said operation information comprises a computer program 48 The thermodilution catheter assembly of claim 47 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 49 The thermodilution catheter assembly of claim 46 wherein said operation information comprises a computer program segment 50 The thermodilution catheter assembly of claim 48 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 51 The thermodilution catheter assembly of claim 46 wherein said operation information comprises a software subroutine 52 The thermodilution catheter assembly of claim 49 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 53 The thermodilution catheter assembly of claim 46 wherein said operation information comprises information for controlling calculation of the patient s cardiac output by an external processing system 54 The thermodilution catheter assembly of claim 50 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 55 A thermodilution catheter system for use in determin ing cardiac output of a patient comprising i a catheter adapted to be inserted into a bloodstream of the patient said catheter comprising A a heating filament 1 made of a thin and flexible mater
3. i a catheter adapted to be inserted into the patient s bloodstream said catheter having a heating filament made of a thin flexible material having a tempera ture coefficient of resistance of at least 0 001 ohms per ohm degree centigrade and ii a memory which resides at a predetermined location on or about said catheter said memory storing encoded thermodilution information comprising 5 720 293 17 a heating filament calibration information said heating filament calibration information compris ing 1 heating filament electrical resistance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament and 3 heating filament temperature coefficient of resistance of said heating filament b patient specific information iii an electrical connector electrically connected to said heating filament and at said proximal end of said catheter assembly for enabling said heating filament to communicate with said external processing system wherein said predetermined location is at said connector and said connector comprises electri cal leads which are electrically connected to said memory and B an external processing system which is connectable to said catheter assembly so that the external processing system can communicate with said memory and said heating filament said external processing system com prising i means for decoding said encoded heating filament cal
4. al 128 303 14 4 185 632 1 1980 Shaw nt 128 303 1 List continued on next page FOREIGN PATENT DOCUMENTS 0221357 5 1987 0235811 9 1987 0303 757 2 1989 0378234 7 1990 ET T 0 417 781 8505475 WO91 03208 3 1991 European Pat Off 5 1985 WIPO 3 1991 WIPO OTHER PUBLICATIONS Transtracheal Doppler A New Procedures for Continuous Cardiac Output Measurement Abrams et al Anesthesiol ogy vol 70 No 1 Jan 1989 pp 134 138 A Thermoelectric Blood Flow Recorder in the Form of a Needle Gibbs 1933 vol 41 pp 141 146 Measurement of Cardiac Output in Anaesthetized Animals By a Thermo Dilution Method Fegler Quarterly Journal of Experimental Physiology 195 vol 39 pp 153 164 List continued on next page Primary Examiner Robert L Nasser Attorney Agent or Firm Oblon Spivak McClelland Maier amp Neustadt Bruce Canter 57 ABSTRACT Acatheter assembly having a catheter 100 with at least one transducer 110 associated therewith for directly measuring physiological parameters of a patient or measuring an amount of a parameter indicative of a physiological condi tion of the patient and a memory 102 which resides at a predetermined location on said catheter 100 The memory 102 contains encoded calibration information for calibrat ing the transducers 110 and encoded patient specific infor mation which can be accessed by an external processing system to wh
5. floating gates operates at 700 Khz and is designed to endure 10 000 erase write cycles and a data retention of 10 years However those skilled in the art will realize that other memory devices will satisfy the characteristics of the present invention The allocation and use of memory 102 will now be described In particular the algorithm used to encode and decode the data stored in the EEPROM of several models of thermodilution catheters will be described As noted above the purpose of encoding the data in the catheter EEPROM is to make it more difficult to copy or 45 55 65 12 counterfeit the catheters in which the present invention is used such as the catheters described in the parent applica tion For this purpose an algorithm is used to encode selected bytes of data within the catheter EEPROM For example in a preferred embodiment the first two 2 bytes of data in the EEPROM need not be encoded This allows the software of the external processing device to read the security code in those bytes This code is the basis of an encrypting decrypting key for the remainder of the stored data Several other bytes also need not be encoded such as bytes 02 through 07 and preferably contain product infor mation such as model number and serial number and the like which may also be read by the software of the external processing device The remaining bytes are encoded and are initialized to contain the manufacturer s copyright no
6. is moved In particular the catheter of the invention contains in the body connector or some other aspect of the catheter a memory 102 which can be accessed by any of a variety of means when the catheter is connected to an external pro cessing device such as a cardiac output computer The memory 102 is either of a volatile or nonvolatile type such that when the memory 102 is not connected to the external processing device the memory contents are not lost In addition the external processing device is preferably allowed when connected to the catheter 100 and conse quently to the memory 102 to address any byte of the memory 102 and to either read or write to the byte at that address In addition the relevant information can be written to the appropriate address of the memory 102 during the portion of the manufacturing process during which the calibration data is measured In a preferred embodiment of the invention different segments of the memory 102 may contain any or all of the following information segments 1 A catheter unique serial number 2 Manufacturing identification data such as calibration manufacture sterilization and ship date or any other date and time information relevant to the catheter 100 5 720 293 11 3 Asoftware program segment which is not integral to the catheter 100 or to any aspect of the catheter 100 or catheter transducer 110 but is instead program information such as a subroutine which is inc
7. unauthorized access The present invention has been designed to meet these needs SUMMARY OF THE INVENTION The above mentioned and other problems of the prior art are resolved in accordance with the present invention by providing a catheter apparatus with an integral memory for retaining information specific to factory calibration patient calibration data patient historical data encoded data and the like For example a presently preferred embodiment of the invention relates to a multilumen flow directed pulmonary artery catheter which has associated therewith one or more transducers for measuring different transducer and physi ological parameters of the patient when the catheter is placed in various vessels lumens bladders orifices cham bers and other body spaces of the patient Such a system is described by way of example in the aforementioned parent application for use with the processing circuitry of U S Pat 10 15 25 35 45 55 65 4 No 5 146 414 to McKown et al both of which have been assigned to the same assignee as the present invention In accordance with the techniques set forth in these patent applications several parameters are measured such as tem perature using a thermistor or thermocouple cardiac out put which requires the transfer of indicator from a trans ducer such as a heater filament to the flowing blood and the measurement of the response at the distal thermistor and oxygen satura
8. Pat No 4 418 392 a measuring device having a measurement cor recting module with a memory unit for storing correction data which is used to correct digitized transducer data However this system requires the measured data to be altered at the analog to digital converter It is desired that such modifications of the raw data be avoided to ensure accuracy Similarly Bailey describes in U S Pat No 4 446 715 using correcting means responsive to calibration means for correcting the measured physical variable This is done for pressure transducers which are not catheter based by using information from a ROM Read Only Memory to correct the transducer output without any incorporation of the information into a microprocessor program However as with the system of Hata this system requires the raw data to be modified Other disclosures directed to calibration of non catheter based sensors using a memory device include U S Pat No 4 481 804 to Eberhard et al U S Pat No 4 499 547 to Inuiya et al U S Pat No 4 611 304 to Butenko et al U S Pat No 4 868 476 to Respaut and U S Pat No 4 942 877 to Sakai et al New Jr et al describe in U S Pat Nos 4 770 179 4 700 708 and 4 621 643 an oximeter with a calibration system however this system uses a resistor to code the LED information for the pulse oximeter Similarly Vandervelden in U S Pat No 4 856 530 describes a cali bration system using a capacitor to store the calibra
9. United States Patent Quinn et al LLL E E HD LLL LO US005720293A 5 720 293 Feb 24 1998 11 Patent Number 45 Date of Patent 54 DIAGNOSTIC CATHETER WITH MEMORY 75 Inventors Michael D Quinn Mark L Yelderman both of Plano Tex 73 Assignee Baxter International Inc Deerfield Til 21 Appl No 245 727 22 Filed May 18 1994 Related U S Application Data 63 Continuation in part of Ser No 769 536 Oct 1 1991 abandoned which is a continuation in part of Ser No 647 578 Jan 29 1991 abandoned and a continuation in part of Ser No 49 231 Apr 19 1993 which is a continu ation in part of Ser No 647 578 Jan 29 1991 abandoned 51 Int CRE ssec 618 5 02 52 U S Cl 128 692 128 713 128 736 58 Field of Search 128 692 713 128 673 5 691 4 632 15 627 56 References Cited U S PATENT DOCUMENTS 3 075 515 1 1963 Richards 128 2 05 3 359 974 12 1967 Khalil 128 2 05 3 595 079 7 1971 Grahn 73 204 3 634 904 1 1972 Blake etal 29 447 3 720 199 3 1973 Rishton et al 128 1 D 3 746 003 7 1973 Blake et al 128 349 3 790 910 2 1974 McCormack 235 151 3 3 798 967 3 1974 Gieles et al 73 204 3 995 623 12 1976 Blake et al 4 073287 2 1978 Bradley et al 128 2R 4 089 336 5 1978 Cage et al 128 303 1 4 001 813 5 1978 Shaw et
10. a CAT93C46 1 Kbit Serial EEPROM FIG 3 and 4 respectively illustrate top and side views of the catheter connector assembly at the proximal end of a catheter having a memory in accordance with the invention FIG 5 illustrates an end view of a connector cover for covering the catheter connector assembly shown in FIG 3 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A system with the above mentioned beneficial features in accordance with presently preferred exemplary embodi 5 720 293 7 ments of the invention will be described below in detail with reference to FIGS 1 5 Although the present invention is described for use with a thermodilution catheter in the preferred embodiment it will be appreciated by those of ordinary skill in the art that the description given herein is for exemplary purposes only and is not intended in any way to limit the scope of the invention All questions regarding the scope of the invention may be resolved by referring to the appended claims In a preferred embodiment a thermodilution catheter has a heating filament which resides internal to the catheter body either in a preformed catheter lumen or beneath an outer sheath and which preferably does not directly contact the blood The heating filament is preferably made of a thin flexible material which may be wrapped either on the exterior of the catheter body wall and then covered by an external sheath material so that the heating filament mater
11. aid heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament or 3 heating filament temperature coefficient of resis tance of said heating filament and b operation information comprising at least one of 1 a computer program 2 a computer program segment and 3 a software subroutine 28 The thermodilution catheter assembly of claim 27 wherein said operation information comprises information for controlling processing of said thermodilution informa tion 29 The thermodilution catheter assembly of claim 28 wherein said operation information comprises information 5 720 293 19 for controlling processing of said thermodilution informa tion to verify correct or modify said thermodilution infor mation 30 The thermodilution catheter assembly of claim 28 wherein said operation information comprises information for controlling processing of said thermodilution informa tion by an external processing system to verify correct or modify said thermodilution information 31 The thermodilution catheter assembly of claim 28 wherein said operation information comprises information for controlling processing of said thermodilution informa tion for calculating the patient s cardiac output 32 A thermodilution catheter assembly system for calcu lating a patient s cardiac output comprising A a catheter assembly comprising i a catheter adapted to be insert
12. ance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament and 3 heating filament temperature coefficient of resistance of said heating filament and B an external processing system which is connectable to said catheter assembly so that the external processing system can communicate with said memory and said heating filament said external processing system com prising i means for decoding said encoded heating filament calibration information stored in said memory for 10 35 18 generating decoded heating filament calibration information and ii means for calculating cardiac output using said decoded heating filament calibration information and wherein said memory further contains at least one of a computer program a computer program segment and a software subroutine which can be read by said external processing system and used thereby to verify correct or modify processing of said thermodilution information 24 A thermodilution catheter assembly for use in deter mining a patient s cardiac output comprising i a catheter adapted to be inserted into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a temperature coefficient of resistance of greater than 0 001 ohms per ohm degree centigrade and ii a memory which resides at a predetermined location on or about said catheter said memory storing
13. and type manufacturer s name and address and any other unique identification or process information In addition the memory may also contain a computer program a computer program segment a software subroutine and computer memory addresses which can be read by the external pro cessing system and used thereby to verify correct or modify the processing of the catheter transducer information In such an embodiment the software of the catheter memory and the external processing system together form a unique software combination such that system operation cannot occur without the two software pieces together This assures that only catheter memories programmed by particular manufacturers can be used with a particular processing system For this purpose the memory may further contain a proprietary code which is read to determine whether the catheter assembly is supplied by a particular manufacturer BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects and advantages of the invention will become more apparent and more readily appreciated from the following detailed description of the presently preferred exemplary embodiment of the invention taken in conjunction with the accompanying drawings of which FIG 1 illustrates a calibration circuit having a memory in accordance with a presently preferred embodiment of the invention FIG 2 illustrates in more detail the connections of the memory of FIG 1 for the case where the memory is
14. ardiac Output Computer Based on Ther 4 684245 8 1987 Goldring wee 356 41 TAE 4 685470 8 1987 Sekii et al 128 692 modilution Principles R A Normann et al Annals of 4 700 708 10 1987 New Jr et al 128 633 Biomedical Eng vol 17 pp 61 73 1989 4 708 777 11 1987 Kuraoka 204A T Investigation of a Continuous Heating Cooling Technique 4 718 423 1 1988 Willis et al ee 128 634 for Cardiac Output Measurement Kevin C Ehlers et al 4 722 347 2 1988 Abrams et al 63 Annals of Biomecial Eng vol 15 pp 551 565 1987 4 733 660 3 1988 Segal serene 128 663 Cardiac Output Estimation by a Thermodilution Method toe 7 1988 Swendson F 128 786 Involving Intravascular Heating and Thermistor Recording 4 770 1 9 9 1988 New Jr et al 128 633 T Barankay et al Acta Physiologica Academiae Scien 4 785 823 11 1988 Eggers et al 128 692 H 2 1 4 796 640 1 1989 Webler 7 128 736 tiarum Hungaricae Tomus 38 2 3 pp 167 173 970 4 814 586 3 1989 Grise 219 549 Measurement of Cardiac Output by Thermal Dilution and 4 819 655 4 1989 Webler 128 713 Direct Fick Methods in Dogs H H Khalil et al Journal of 4 832 504 5 1989 Hori et al 374 183 Appl Physiol vol 21 3 pp 1131 5 1966 4 841 981 6 1989 Tanabe et al 128 692 Determination of Cardiac Output in Man by a New Method 4 856 530 8 1989 Vandervelden 128 692 Based on Thermodi
15. asured by the second transducer for use by the external processing system to measure oxygen saturation oxygen tension PaO pH level PCO concentration elec trolyte concentration e g sodium potassium chloride bicarbonate and glucose and the like However the detec tion transducers used in accordance with the invention may measure naturally occurring substances parameters or other physiological events which have not been supplemented with an energy or other type of introduction transducer such as a temperature pressure or ion concentration transducer Accordingly the technique of the invention is not limited to use with heat temperature optical energy or indicator type transducers In accordance with another aspect of the invention the connector leads are connected such that the external pro cessing system can write calibration information to the memory of the catheter during operation for in vivo cali bration This information may then be used during process ing of the detected data to make necessary corrections or modificiations to the transducer outputs or the subsequent computations using the raw information received from the transducers During operation the external processing system may access the patient specific information in the memory via the connector leads so that the memory may provide historical patient information to the external processing system for display as trending data of the patient This informa
16. atu ration However for particular catheter mounted transducers certain errors are present Some errors are inherent in the design of the transducer some are caused by variations in the transducer as a result of manufacturing processes some are caused by changes in the transducer due to aging or use and some are patient specific Although such errors can be measured several practical problems arise For example although design or manufacturing errors can be measured for each individual transducer that information must be conveyed to either the end user or to a monitor or measuring device so that the errors may be compensated For example Lentz et al describe in U S Pat No 4 407 298 a connector for a thermodilution catheter which joins the catheter to an 10 15 35 45 55 65 2 output computer However the device of Lentz et al simply uses individual bit lines each of which can be either open or closed so that four different coded states reflecting the size of the catheter are possible and does not relay information about the transducers themselves to the output computer While Lentz et al do not describe that information about the transducers may be contained on the catheter other prior art catheter sensors utilize a memory unit which is connected to the sensors and to signal processing circuitry For example Meinema describes in U S Pat No 4 858 615 an integral sensor and memory combination unit wher
17. d heating filament said external processing system com prising i means for decoding said encoded heating filament calibration information stored in said memory for generating decoded heating filament calibration information and ii means for calculating cardiac output using said decoded heating filament calibration information 12 The thermodilution catheter assembly system of claim 11 wherein said catheter assembly further comprises iii means mounted to said catheter and coupled to said external processing system for measuring resistance of said heating filament and said catheter assembly system further comprises C means coupled to said external processing system and said heating filament for controlling the tem perature of said heating filament based upon said resistance of said heating filament and the decoded calibration information 13 The thermodilution catheter assembly system of claim 12 wherein said means for controlling the temperature includes means for reducing electrical power transmitted to said heating filament when the resistance of said heating filament exceeds a predetermined resistance value 14 The thermodilution catheter assembly system of claim 11 further comprising a battery located in proximity of said memory for providing power to said memory when said memory is not connected to said external processing system 15 The thermodilution catheter assembly system of claim 11 wherein said memory i
18. e disposed on or about the catheter The memory of the invention may be disposed at different locations within the catheter assembly For example the memory may be disposed within the body of the catheter in an area adjacent one of the transducers or in a connector connected to a proximal end of the catheter assembly for allowing at least one transducer of the catheter to communicate with the processing system which may be a conventional external processing system or computer Such a connector preferably comprises leads which are connected to the memory so as to allow access to contents of the memory by the external processing system connected to the catheter The catheter of the invention may be of different types and may include transducers of different types For example the catheter may be designed for single patient use or multiple patient use Also the transducers of the catheter preferably comprise a first transducer for introducing energy or a physical indicator into a physiological medium of the patient and a second transducer for directly measuring physiological parameters of the physiological medium in response to the energy or physical indicator which has either passed through the physiological medium or passed directly from the first transducer to the second transducer In a particular embodiment the first transducer may be a heating element and the second transducer may be either a thermistor or a thermocouple for measuring tem
19. e in deter mining a patient s cardiac output comprising a catheter adapted to be inserted into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a temperature coefficient of resistance of at least 0 001 ohms per ohm degree centigrade and a memory which resides at a predetermined location on or about said catheter said memory storing thermodilu tion information comprising patient specific informa tion 38 A thermodilution catheter assembly of claim 37 wherein said patient specific information comprises patient historical data 39 A thermodilution catheter assembly for use in deter mining a cardiac output of a patient comprising a catheter adapted to be inserted into a bloodstream of the patient said catheter having a heating filament made of a thin flexible material having a temperature coeffi cient of resistance of greater than zero and a memory which resides at a predetermined location on or about said catheter said memory storing thermodilu tion information comprising heating filament calibra tion information 40 The thermodilution catheter assembly of claim 39 wherein said heating filament calibration information com prises heating filament electrical resistance of said heating filament at a given temperature 41 The thermodilution catheter assembly of claim 40 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centig
20. e infor mation regarding the characteristics of the sensor or sensor memory combination are permanently recorded in the memory and the sensor and memory are indissolubly coupled together The recorded information such as data for linearizing the sensor outputs is automatically read and retrieved by separate electronic processing circuitry However the system of Meinema is described only for transducers which receive naturally occurring physiological parameters and is not described for use with transducers which measure responses to energy or outputs from other introducing type transducers In addition Meinema corrects the transducer responses for both amplitude and offset and is concerned only with displaying a corrected physiological parameter As a result Meinema does not consider correct ing or modifying the transducer for calculation estimation or computation of derived measurements Furthermore Meinema gives no consideration to correcting modifying compensating for energy indicating or delivering substances via introduction transducers It is thus desirable that sensor memory systems of the type taught by Meinema be expanded to include the above mentioned capabilities as well as other capabilities to be described in the following detailed description of the invention Non catheter based measuring systems frequently have provided correcting means comprising memories for storing correction data For example Hata describes in U S
21. e other hand active electronic components including numerous nonlinear com ponents may be used such that a particular performance corresponds to a particular calibration number or value Such calibration information is preferably stored in a memory component such as a ROM Read Only Memory RAM Random Access Memory nonvolatile memory devices or other types of volatile or nonvolatile memory or digital devices of any desired size The calibration informa tion preferably includes codes that represent the filament resistance filament efficiency and other parameters If prop erly selected one or more electronic components may be used to encode the calibration information of the thermistor or thermocouple such as its value and the filament resistance filament efficiency and other parameters Thus the calibration information for both the thermistor or thermocouple and the heating filament may be encoded by one or more active or passive electronic components or these values may be stored in a suitable memory device The cardiac output computer may then decode this information and incorporate it into the calculation of cardiac output for example However this step may be eliminated if the actual appropriate software is contained in the catheter itself For example a memory device such as a ROM may be contained in the catheter with a portion of the software utilized by the cardiac output computer resident within it Such information mig
22. e with the invention to pass the calibration information Prior art thermodilution catheters and pulse oximeter sensors have used resistors to code the values for thermistors or LEDs For example New Jr et al in the aforementioned U S Pat No 4 700 708 use a resistor to calibrate LED wavelengths on a pulse oximeter However the present inventors know of no previous attempt to code the filament calibration for transferring the calibration information of the heating filament solely or the calibration information of the heating filament and thermistor or thermocouple together Thus in accordance with the present invention calibration of the heating element may be conducted by measuring the heater resistance at a known temperature The catheter assembly can then use the previously calibrated thermistor or thermocouple and a built in ohm meter to establish a calibrated reference point for the heater element This approach has the advantage of calibrating the heater imme diately prior to use in a patient at the patient s body temperature Such an accurate calibration of heater resis tance and temperature is necessary to accurately monitor heater temperature to insure patient safety The calibration circuit of the invention may include passive electronic components such as resistors inductors and capacitors such that the value of the components cor respond to a particular calibration value or number accord ing to a predetermined table On th
23. ectly detected as an increasing filament resistance which reduces the power delivered to the heating filament In this manner the actual current and voltage to the catheter fila ment may be continuously monitored From the values of current and voltage a delivered power may be calculated which is needed to calculate flow and the filament resistance may be calculated and used for computing the filament temperature Thus at all times the actual filament tempera ture is known In the calculation of cardiac output using a thermodilution catheter and an associated processing system it is necessary to know certain properties about the measuring transducer such as a thermistor or thermocouple and the heat applica tion or heating filament efficiency for in the manufacturing process it is difficult to produce either thermistors or ther 5 720 293 9 mocouples or heating filaments which uniformly have the same properties Thus to reduce the errors which would be introduced into the calculation of cardiac output due to these variances it is necessary to calibrate or measure the physical properties of both the thermistor or thermocouple and the heating filament Since in a clinical environment each car diac output computer may be attached over time to various pulmonary artery catheters and to eliminate the need for the user to manually transcribe these calibration numbers to the computer a coding technique has been developed in accor danc
24. ed into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a tempera ture coefficient of resistance of at least 0 001 ohms per ohm degree centigrade ii a memory which resides at a predetermined location on or about said catheter said memory storing ther modilution information comprising a heating filament calibration information said heating filament calibration information compris ing at least one of 1 heating filament electrical resistance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament or 3 heating filament temperature coefficient of resistance of said heating filament and b operation information comprising at least one of 1 a computer program 2 a computer program segment and 3 a software subroutine B an external processing system adapted to communi cate with said memory to read said thermodilution information and to communicate with said heating filament to determine resistance of said heating fila ment and wherein said external processing system and said operation information in combination comprise means for calculating the patient s cardiac output by processing said thermodilution information 33 The thermodilution catheter assembly system of claim 32 wherein said operation information comprises informa tion for controlling processing of said thermodilution infor ma
25. electrical leads to enable access to said encoded thermodilution information stored in said memory by said external processing system 19 The thermodilution catheter assembly system of claim 18 wherein said electrical leads are electrically connected to said memory such that said external processing system can write calibration information for either said patient or said heating filament to said memory for in vivo calibration 20 The thermodilution catheter assembly system of claim 11 wherein said catheter assembly further comprises one of thermistor and a thermocouple for measuring temperature changes in the patient s bloodstream caused by heat gener ated in said heating filament 21 The thermodilution catheter assembly system of claim 20 wherein said heating filament is adapted to supply thermal energy to the patient s bloodstream and the thermistor or thermocouple is adapted to measure the effects of the thermal energy supplied to the patient s bloodstream by heat generated in said heating filament said external processing system is adapted to calculate one of blood flow and cardiac output of said patient based upon measurements by said thermistor or ther mocouple of said effects of the thermal energy supplied to the patient s bloodstream 22 A thermodilution catheter assembly system for calcu lating a patient s cardiac output comprising A a catheter assembly having a distal end and a proximal end and comprising
26. em the catheter can be easily replicated by a competitor and manufactured and sold with out the display device resulting in a significant loss of profits for the original manufacturer This can be somewhat prevented if the catheter and display device have some mechanism by which a competing manufacturer may be prevented from copying the catheter alone and selling it in place of the original catheter A suitable mechanism of this type is desired Previous inventors have addressed this problem by designing various types of devices for encoding transducer factors for calibration For example Houvig in U S Pat No 4 303 984 places in a common connector a ROM shift register and other sensor electronics powered by a power supply which is also included in the same connector In the Houvig device when the ROM information is desired the information is clocked from the ROM and is combined or superimposed onto the raw sensor electronics However such an arrangement is unduly complicated and expensive for use in a diagnostic catheter of the type to which the present invention is directed A simpler and less expensive alternative is desired Accordingly it is desired to provide a catheter with memory which can overcome the above mentioned prob lems by retaining the information specific to factory calibration patient specific calibration data historical patient data and the like It is also desirable that this information be coded to prevent
27. er assembly of claim 1 wherein said thermodilution information further comprises b a proprietary code said heating filament calibration information that is stored in said memory is stored in said memory as encoded heating filament calibration information in an encoded form that is based upon said proprietary code such that said encoded heating filament calibration information can be decoded using said proprietary code and said catheter is adapted so that said memory is readable and decodable by the external processing system 3 The thermodilution catheter assembly of claim 2 wherein said memory stores said proprietary code in the form of a proprietary binary code said catheter and said memory being adapted so that said proprietary binary code is accessible by the external processing system and said proprietary binary code and said encoded heating filament calibration information are interrelated so that said encoded heating filament calibration information is decodable using said proprietary binary code by the external processing system 4 The thermodilution catheter assembly of claim 1 wherein said predetermined location is within said catheter 5 The thermodilution catheter assembly of claim 1 wherein said predetermined location is adjacent said heating filament 6 The thermodilution catheter assembly of claim 1 wherein said catheter assembly has a proximal end and a distal end said catheter assembly further compr
28. he temperature become excessive damage could result to the surrounding blood and tissues Normally a second temperature sensing device such as a thermistor or thermocouple would need to be embedded next to the filament to measure its temperature However by using a filament material which has a high temperature coefficient of resistance as herein described not only can it be used as a heat supplier but it can also serve as its own temperature sensing device For example resistance of any material is measured as follows d where p is the resistivity 1 is the length and A is the cross sectional area Then and if a the mean temperature coefficient of resistivity is defined as 15 25 35 55 65 8 Ap a CAT A P where Ap is the change in the coefficient and AT is the change in temperature then Then by measuring the current i and the voltage v both delivered power and resistance of the filament can be simultaneously measured as Av Ai AR When a thermodilution catheter in accordance with the invention is connected to a cardiac output computer via a heater connector an electrical current is applied to the heating filament in the form of pulses When the heating filament is activated an approximate average of 7 5 watts of power may be delivered to the heating filament During operation as described above the cardiac output computer may continuously measure and moni
29. ht include program segments or historical patient data Thus when the catheter is connected to the cardiac output computer prior to the beginning of processing for determin ing the cardiac output the software or program segment contained in the catheter memory device ROM or RAM may be transferred to the main software program of the 10 15 35 45 55 65 10 cardiac output computer This feature of the invention also provides an additional safety feature for the cardiac output computer will not start until it has transferred the program segment and incorporated this segment into its own pro gram The calibration circuitry of the type just described can be seen by way of example in FIG 1 As should be apparent to one of ordinary skill in the art the calibration circuit of FIG 1 is quite different from that used in typical prior art thermodilution catheters In particular classic thermodilu tion catheters use calibration resistances which are con nected to form one half of a bridge circuit with the ther mistor or thermocouple In such devices the reference resistor is selected to match the thermistor or thermocouple for a standard temperature In this manner compensation for variability in the thermistors or thermocouples may be achieved However by using the calibration circuit of the invention whereby a RAM or ROM containing calibration data is included within the connector of the catheter such a reference resist
30. ial 2 having a resistance and 3 having a temperature coefficient of resistance of greater than zero and 15 20 25 35 22 B a memory said memory storing thermodilution information comprising heating filament calibration information for said heating filament and ii means coupled to said memory and said heating filament for controlling the temperature of said heating filament based at least in part upon said heating fila ment calibration information stored in said memory 56 The thermodilution catheter system of claim 55 wherein said heating filament calibration information stored in said memory comprises the heating filament electrical resistance of said heating filament at a given temperature 57 The thermodilution catheter system of claim 56 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 58 The thermodilution catheter system of claim 55 wherein said heating filament calibration information stored in said memory comprises the heating filament heat transfer efficiency of said heating filament 59 The thermodilution catheter system of claim 57 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 60 The thermodilution catheter system of claim 55 wherein said heating filament calibration information stored in said memory comprises the heating filament temperature coefficient of resistance of said heating f
31. ial is not exposed to the blood or on the outer surface of a supporting sheath inserted into the catheter lumen The heating filament so designed supplies a quantity of heat to the flowing blood which is used for measuring the volumet ric blood flow using an indicator dilution equation In a preferred embodiment the heating filament is comprised of a material having a high temperature coefficient of resistance whereby resistance of the heating filament is inversely proportional to its temperature ie it has a negative temperature coefficient of resistance This aspect of the invention enables power to the heating filament to be reduced when resistance of the heating filament exceeds a predetermined resistance amount which is reached when the temperature of the heating filament reaches approximately 52 C A material suitable for the heating filament thus has a temperature coefficient of resistance greater than 0 001 Q Q C Also such a material preferably has a low thermal capacitance and high thermal conductivity Preferred heating filament materials include an alloy of approximately 7096 nickel and 3096 iron and an alloy of approximately 2996 nickel 17 cobalt and 54 iron During operation since the heating filament formed as described above is used primarily to insert heat into the blood stream it will rise to a temperature higher than the surrounding environment Thus it is necessary to know the filament temperature since should t
32. ibration information stored in said memory for generating decoded heating filament calibration information and ii means for calculating cardiac output using said decoded heating filament calibration information iii means for displaying said patient specific informa tion as trending data wherein i said connector and said memory are functionally interrelated by said electrical leads to enable access to said encoded thermodilution information stored in said memory by said external processing system and system of claim 18 ii said external processing system said connector and said memory are functionally interrelated so that said external processing system can access said patient specific information that is stored in said memory via said electrical leads 23 A thermodilution catheter assembly system for calcu lating a patient s cardiac output comprising A a catheter assembly comprising i a catheter adapted to be inserted into the patient s bloodstream said catheter having a heating filament made of a thin flexible material having a tempera ture coefficient of resistance of at least 0 001 ohms per ohm degree centigrade and ii a memory which resides at a predetermined location on or about said catheter said memory storing encoded thermodilution information comprising a heating filament calibration information said heating filament calibration information compris ing 2 heating filament electrical resist
33. ich the catheter assembly is connected for processing The memory 102 is further designed such that disconnection of the catheter assembly from the external processing system does not cause values stored in the memory to be lost so that the patient specific information need be reentered into the memory when the catheter assembly is reconnected to the same or another external processing system By so providing the catheter assembly with memory 102 information for factory calibration patient calibration and historical patient data may be stored with the catheter 100 for ease of use The data in the memory 102 may also be coded to prevent easy replication of the catheter 100 by a competing manufacturer 64 Claims 3 Drawing Sheets l i l l 5 720 293 Page 2 U S PATENT DOCUMENTS 5214267 5 1993 Hoshi et al 219 497 5 217 019 6 1993 Hughes 128 668 4 198 957 4 1980 Cage et al 1281R 5 261 411 11 1993 Hughes 128 668 4 199 816 4 1980 Humphrey 364 571 5271191 1 1994 Hughes 128 692 4 206 759 6 1980 Shaw 128 303 1 5 383 874 1 1995 Jackson et al Le 606 41 4 207 896 6 1980 Shaw 128 303 1 4 209 017 6 1980 Shaw 128 303 1 OTHER PUBLICATIONS 4 236 527 12 1980 Newbower et al 128 692 4240 41 12 1980 Khalil 128 692 Studies on the Destruction of Red Bl
34. ilament 10 The thermodilution catheter assembly of claim 9 wherein said heating filament is adapted to supply thermal energy to the patient s bloodstream and the thermistor or thermocouple is adapted to measure the effects of thermal energy supplied to the patient s bloodstream for use by the external processing system to calculate one of blood flow of the patient and cardiac output of the patient 11 A thermodilution catheter assembly system for calcu lating a patient s cardiac output comprising A a catheter assembly comprising i a catheter adapted to be inserted into the patient s bloodstream said catheter having a heating filament made of a thin flexible material having a tempera ture coefficient of resistance of at least 0 001 ohms per ohm degree centigrade ii a memory which resides at a predetermined location on or about said catheter said memory storing encoded thermodilution information comprising a heating filament calibration information said heating filament calibration information compris ing 1 heating filament electrical resistance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament and 3 heating filament temperature coefficient of resistance of said heating filament and B an external processing system which is connectable to said catheter assembly so that the external processing system can communicate with said memory and sai
35. ilament 61 The thermodilution catheter system of claim 58 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 62 The thermodilution catheter system of claim 55 wherein said thermodilution information further comprises patient specific information 63 The thermodilution catheter system of claim 55 wherein said memory further stores at least one of a com puter program a computer program segment and a software subroutine 64 The thermodilution catheter system of claim 63 wherein said at least one of a computer program a computer program segment and a software subroutine can be used to verify correct or modify processing of said thermodilution information
36. information historical information and the like which is not lost when the catheter is disconnected from its associated display device 2 Description of the Prior Art Diagnostic catheters have been constructed in various configurations and used in medicine for a multitude of purposes Such catheters are designed to reside within lumens chambers orifices and tissues of various organs including arteries veins the heart and the like Medical catheters have been used as conduits to either infuse fluids or drugs or as conduits for connecting intra vascular or organ fluids to transducers for measuring pressure flow temperature oxygen saturation and the like Catheters have also been used to assist in blood circulation as described for example by Rishton et al in U S Pat No 3 720 199 which relates to an intra aortic balloon catheter assembly which is implanted in the descending aorta and connected to instru mentation to inflate deflate the balloon synchronously with the cardiac cycle Medical catheters also have been constructed such that transducers can be mounted directly on the catheter either at the tip on the surface or within the catheter body for measuring physiologic parameters and sending the informa tion directly to a monitor or display device Such transducers include catheter mounted thermistors for measuring temperature pressure transducers for measuring hydrostatic pressure and oximeters for measuring blood oxygen s
37. ising iii a connector at said proximal end of said catheter assembly said connector being electrically con nected to said heating filament said connector being adapted to connect to the external processing system so that said heating filament can communicate with the external processing system and wherein said predetermined location is at said connector 7 The thermodilution catheter assembly of claim 6 wherein said connector comprises electrical leads which are connected to said memory said electrical leads and said connector are functionally interrelated to enable access through said connector via said electrical leads to said encoded heating filament calibration information and said proprietary code that are stored in said memory 8 The thermodilution catheter assembly of claim 7 wherein said connector is functionally interrelated to said memory via said electrical leads and said connector is structured so that thermodilution infor mation can be written into said memory via said leads by electrical signals received by said connector while said connector receives thermodilution signals from said catheter thereby enabling in vivo calibration 5 720 293 15 9 The thermodilution catheter assembly of claim 1 wherein said catheter assembly further comprises one of a thermistor and a thermocouple mounted on said catheter for measuring temperature changes in the patient s bloodstream caused by heat generated in said heating f
38. luding pulse oximeters transcutaneous oxygen elec trodes and the like In one preferred embodiment wherein the catheter has a heating filament and a temperature detecting means cali brating means are provided for calibrating both the heating filament and the temperature detecting means Preferably the calibrating means comprises a Read Only Memory ROM contained within the catheter member for storing calibration information for either or both the heating fila ment and the temperature detecting means as well as any other necessary information Preferably the ROM is located at the proximal end of the catheter and includes calibration information relating to heating filament resistance at a given temperature heating filament heat transfer efficiency tem perature coefficient of resistance and thermistor information Moreover the ROM may be connected to a cardiac output computer so as to pass a program segment stored in the ROM of a program used by the cardiac output computer to calculate cardiac output of the patient whereby calculation of the patient s cardiac output cannot commence until the cardiac output computer is connected to the ROM and the program segment transferred to the cardiac output computer In accordance with yet another aspect of the invention the memory may further contain catheter identification infor mation including manufacture date batch number steriliza tion date expiration date catheter transducer number
39. lution H H Khalil et al Preliminary 4 858 615 8 1989 Meinema 128 668 Communications Jun 22 1963 pp 1352 4 5 ERER O X d Repeated or Continual Measurements of Cardiac Output in 2 1990 E s 192 69 the Squirrel Monkey Saimiri sciureus by Thermodilution 4941 75 7 1990 Williams et al 128 692 H H Khalil Bureau of Med and Surgery MR011 01 4 4 942 877 7 1990 Sakai et al 128 633 Naval Aerospace Med Inst Mar 8 1968 4 947 852 8 1990 Nassi et al 128 662 CRC Handbook of Chemistry and Physics 60th Ed 4 951 682 8 1990 Petre 128 713 1979 1980 p E 85 Cole Parmer Instrument Co Niles I1 4 954 318 9 1990 Yafuso et al 422 059 Catalog pp 1259 61 5 007 423 4 1991 Branstetter et al 128 633 Baxter healthcare Corp Catalog pp 1 2 5 and 6 Jun pei Sod m nen DUIS 1992 Service Manual for Model COM 1 Thermodilution 046 5 a Cardiac Output Computer American Edwards Laboratories 5 047 025 9 1991 Taylor et al 606 31 J 1984 6 Table 2 1 5 056 526 10 1991 Khalil 128 692 Un ome po Di LE ens 5 080 106 1 1992 Sekii et al 128 692 Continuous Thermal Measurement of Cardiac Output 5 121 749 6 1992 Nassi et al 128 692 Philip et al Transactions on Biomedical Engineering vol 5 158 082 10 1992 Jones Lecce 128 633 SME 31 No 5 May 1984 pp 393 400 5 720 293 Sheet 1 of 3 Feb 24 1998 U S Patent 8 200
40. nserted into the patient and connected to the monitor As described above the information in the memory 102 is accessible and changeable by the external computing calculation display or monitoring means in the field during clinical use However before the catheter memory 102 leaves the factory some of information is preferably written 10 15 to the catheter memory 102 including catheter and or trans 30 ducer test calibration or date information Although an exemplary embodiment of the invention has been described in detail above those skilled in the art will readily appreciate that many additional modifications are possible in the exemplary embodiment without materially departing from the novel teachings and advantages of the invention For example the memory 102 may have a small battery backup located on the connector 300 with the memory chip Also the memory 102 may be of any desired size and may be read only or read write memory In addition the memory may be used alone or in combination with a variety of other components such as multiplexers capacitors resistors operational amplifiers and the like and may be used in non catheter applications such as pulse oximeters transcutaneous oxygen electrodes and the like The memory 102 also may be combined directly with other electronic components such as amplifiers resistors capacitors inductors other memory units multiplexers shift registers batteries and the like and f
41. number of seconds since 1 1 70 39 Checksum of all above bytes 40 41 Zero bytes 42 82 Copyright c 1991 Interflo Medical Inc 83 Zero byte 84 126 Random uninitialized data bytes 127 Checksum of all above 127 bytes Then for example the data in the EEPROM after patient data has been collected will appear as follows TABLE 2 Byte Function 34 35 Patient Weight 36 37 Patient Height 38 Reserved 39 Checksum of above five 5 bytes 40 43 Timestamp of Ist CO data point 5 720 293 13 TABLE 2 continued Byte Function 44 45 Count of all CO data points in EEPROM 46 109 Last 64 CO data points at 15 minute intervals 110 Reserved 111 Checksum of bytes 40 through 0 This data is the historical patient data in a preferred embodiment although other data may of course be col lected After manufacture of the catheter assembly of the invention the memory 102 may be accessed by an appro priate device to determine if the code stored in the memory 102 is the proper code If this code is not the proper code then it is known that the catheter assembly being checked is faulty or is an unauthorized copy The tester then may choose to render the tested catheter non functional or tem porarily or permanently inoperative through any of a variety of means In this manner a mechanism is provided to insure that the catheter assembly being used is not an imitation catheter and to prevent such a catheter assembly from being i
42. ood Cells Ham et al 4 303 984 12 1981 Houvig eene 364 571 Blood vol 3 1948 pp 373 403 4 364 390 12 1982 Shaw 128 303 1 Thin Film Thermistors Morris et al Journal of Physics 4 399 823 8 1983 Donnelly 128 736 Engineering Scientific Instruments vol i 1975 pp 4 407 298 10 1983 Lentz et al 128 713 411 414 4 418 392 11 1983 Hata 364 571 Shape and Shape Transformations of Heated Human Red 4 446 715 5 1984 Bailey HAR Cells Ponder J Exp Biol vol 26 1950 pp 35 45 4 481 804 11 1984 Eberhard et al 73 1 G P 1 Instantaneous and Continuous Cardiac Output Obtained 4 499 547 2 1985 Inuiya et al 364 571 E 4 499 907 2 1985 Kallok et al 128 786 with a Doppler Pulmonary Artery Catheter Segal et al 4 507 974 4 1985 Yelderman 73 861 06 Experimental Studies JACC vol 13 No 6 May 1989 pp 4 524264 6 1985 Takeuchi et al 219 497 1382 1392 4 572206 2 1986 Geddes et al 128 692 The Influence of Temperature on Red Cell Deformability 4 576 182 3 1986 Norman 128 692 Williamson et al Blood vol 46 No 4 Oct 1975 pp 4 611 304 9 1986 Butenko et al 364 571 611 624 4 621 643 11 1986 New Jr et al 128 633 The Output of the Heart in dogs Stewart The American 4 632 125 12 1986 Wetler et al 128 692 Joumal of Physiology vol 57 1921 pp 27 50 4 671 295 6 1987 Abrams et al 128 663 A Continuous C
43. or for calibration purposes is not needed Such a memory for use with a thermodilution catheter 100 is shown as memory 102 of connector 104 in FIG 1 Preferably the software module referred to above is stored in the memory 102 and includes such things as the format version for the calibration data trademark information historical patient data such as cardiac output for the previous several hours or whatever information is desired for controlling the cardiac output program Thus by placing the encoded calibration data within the memory 102 and placing the memory 102 on the catheter 100 the reference resistance 106 for the thermistor or thermocouple 108 may be eliminated In addition only a catheter having a memory 102 storing the necessary information for oper ating the program of the cardiac output computer may be used in conjunction with the cardiac output computer to obtain the desired calculation Thus the purpose of the present invention as illustrated in FIG 1 is to disclose a method of enhancing the performance of a catheter or catheters such as those described in the aforementioned related application by retaining factory calibration factory identification computer or monitor spe cific software program segments patient specific calibration information and patient historical information in the cath eter which is not lost when the catheter is disconnected from the computer monitor or other display device as when the patient
44. orpo rated into the software program of the display device 4 A unique security code which allows the monitor to identify a catheter which has been manufactured by the manufacturer of the monitor or a competing manufac turer and 5 Manufacture or calibration information about the energy introduction transducer 110 which is the part of the catheter 100 used to introduce energy into the flowing blood for the thermodilution measurement Such information could contain for example filament or transducer nominal electrical resistance heat trans fer coefficient thermal mass filament composition and coefficient of resistance Of course in view of the present disclosure those skilled in the art will appreciate that other desirable information may be kept in the memory 102 as well The present invention will now be described in more detail with respect to FIGS 2 5 FIG 2 illustrates a schematic for a catheter memory 102 in accordance with a preferred embodiment of the invention As shown a standard thermistor resistor bridge catheter assembly having reference resistor 106 and thermistor 108 may be used as in the embodiment of FIG 1 to measure blood temperature Catheter memory 102 is also provided and is connected as shown to include voltage supply lines VCC clock lines SK data lines DI and DO and a ground GND In the presently preferred embodiment a CAT93C46 1 Kbit serial EEPROM is used as memory 102 and is connected as sho
45. perature changes in the physiological medium caused by the heating element In this embodiment the heating element is prefer ably made of a thin flexible material which may be wrapped either on the exterior of the catheter body wall and then covered by an external sheath material so that the heating element material is not exposed to the blood or on the outer surface of a supporting sheath inserted into the catheter 5 720 293 5 umen During use the heating element temperature is preferably measured simultaneously with the thermodilution measurement without the use of a second measuring trans ducer The heating element temperature is not measured to calculate velocity but rather to insure that a safe heating element temperature may be maintained This is accom plished in one embodiment by forming the heating element of a material which has a resistance proportional or inversely proportional to its temperature On the other hand the first transducer may supply thermal energy ultrasound or electromagnetic energy to the physi ological medium and the effects thereof on the physiological medium may be measured by the second transducer for use by the external processing system to measure blood flow cardiac output and or flow of another physiological sub stance of the patient In addition the first transducer may supply optical energy to a physiological medium of the patient and the effects thereof on the physiological medium may be me
46. rade 42 The thermodilution catheter assembly of claim 39 wherein said heating filament calibration information com prises heating filament heat transfer efficiency of said heat ing filament 43 The thermodilution catheter assembly of claim 41 wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 44 The thermodilution catheter assembly of claim 39 wherein said heating filament calibration information com prises heating filament temperature coefficient of resistance of said heating filament 45 The thermodilution catheter assembly of claim 42 Wherein said temperature coefficient of resistance is at least 0 001 ohms per ohm degree centigrade 46 A thermodilution catheter assembly for providing data to an external processing system for calculating a cardiac output of a patient comprising a catheter adapted to be inserted into a bloodstream of the patient said catheter having a heating filament made of a thin flexibie material having a temperature coeffi cient of resistance of greater than zero means mounted to said catheter for measuring data relating to cardiac output and 5 720 293 21 a memory which resides at a predetermined location on or about said catheter said memory storing operation information for controlling calculation of the patient s cardiac output based upon data including said data relating to cardiac output that is measured by said means for measuring
47. s adapted to be used with means for encoding calibration information in accordance with a 5 15 25 35 55 60 65 16 proprietary code and to be written into with encoded calibration information encoded in accordance with said proprietary code and said memory being further adapted to be read by said external processing system and used thereby to decode said encoded calibration information 16 The thermodilution catheter assembly system of claim 15 wherein said memory comprises means to store said proprietary code in the form of a proprietary binary code and said memory and said catheter assembly are adapted so that said memory can be accessed by said external processing system and used thereby to decode said encoded calibration information 17 The thermodilution catheter assembly system of claim 11 wherein said catheter assembly has a distal end and a proximal end and said catheter assembly further comprising iii an electrical connector electrically connected to said heating filament and at said proximal end of said catheter assembly for enabling said heating filament to communicate with said external processing system wherein said predetermined location is at said connector 18 The thermodilution catheter assembly system of claim 17 wherein said connector comprises electrical leads which are elec trically connected to said memory and said connector and said memory are functionally interre lated by said
48. ther modilution information comprising a heating filament calibration information said heat ing filament calibration information comprising at least one of 1 heating filament electrical resistance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament or 3 heating filament temperature coefficient of resis tance of said heating filament and b patient specific information 25 The thermodilution catheter assembly of claim 24 wherein said patient specific information comprises patient historical data 26 The thermodilution catheter assembly of claim 24 wherein said thermodilution information further comprises catheter identification information 27 A thermodilution catheter assembly for insertion in an artery or a vein for use in determining a patient s cardiac 4o Output comprising 45 55 65 i a catheter adapted to be inserted into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a temperature coefficient of resistance of at least 0 001 ohms per ohm degree centigrade and ii a memory which resides at a predetermined location on or about said catheter said memory storing ther modilution information comprising a heating filament calibration information said heat ing filament calibration information comprising at least one of 1 heating filament electrical resistance of s
49. tice and checksums arithmetic 8 bit sums which may be used by the security algorithm as shown in TABLE 1 below The following algorithm is preferably utilized to encode or decode the stored data First the security code is read from bytes 0 and 01 This code may be for example 0314 Hex but any 16 bit value is possible The checksum in byte 127 is then read and ANDed with the security code This result is then ANDed with the complement of the security code and shifted right four places This forms the encryption decryption key The data to be encrypted or decrypted is exclusive ORed on a word basis with the key The above may be illustrated by a simple C code expression as follows data security_code amp cksum amp security code 4 Also the information related to factory calibration of the catheter filament is preferably stored and read from byte 08 Of course those skilled in the art will readily appreciate that many other types of known encoding schemes may be used For example the proprietary code may also be encrypted in accordance with the invention The data in a preferred embodiment of memory 102 after initialization will thus appear as follows TABLE 1 Byte Function 00 01 Unencoded security code 02 05 Unencoded serial number 06 Unencoded layout byte 07 Unencoded model number 08 Encoded heater resistance 09 32 Encoded remaining data 33 Encoded checksum of above data 34 Zero byte 35 38 Longword
50. tion 34 The thermodilution catheter assembly system of claim 32 wherein said operation information comprises informa tion for controlling processing of said thermodilution infor mation to verify correct or modify said thermodilution information 35 A thermodilution catheter assembly for providing data to an external processing system for calculating a patient s cardiac output comprising i a catheter adapted to be inserted into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a temperature coefficient of resistance of at least 0 001 ohms per ohm degree centigrade ii means mounted to said catheter for measuring data relating to cardiac output and iii a memory which resides at a predetermined location on or about said catheter said memory storing opera 10 15 2 UA 30 35 20 tion information for controlling calculation of the patient s cardiac output based upon data including said data relating to cardiac output that is measured by said means for measuring said operation information com prising at least one of 1 a computer program 2 a computer program segment and 3 a software subroutine 36 The thermodilution catheter assembly of claim 35 wherein said operation information comprises information for controlling calculation of the patient s cardiac output by an external processing system 37 A thermodilution catheter assembly for us
51. tion information In addition although errors which arise once the trans ducer is in use either because of aging or other processes of the transducer or because of patient physiological variations 5 720 293 3 can be measured by in vivo or patient calibration tests again the results must be retained by the measuring device or monitor for display to the end user Moreover a more serious problem is that the transducer once inserted in a patient cannot be removed Rather the inserted transducer must move with the patient Nevertheless when the patient is moved from one critical care environment to another such as from the operating room to the intensive care unit the monitoring equipment is often not moved but rather the catheter is disconnected from the original monitor and reconnected to another monitor in the new location Such disconnection typically results in the loss of transducer specific or patient specific information or requires the opera tor to re enter the information resulting in increased work frustration and reduction in quality of patient care Another problem for catheter manufacturers is that gen erally the catheter is relatively simple in proportion to the complexity of the computing calibration and display devices yet the profits are made from the sale of the catheters not the monitors As a result even though a manufacturer may develop manufacture and sell the cath eter and display device as a syst
52. tion is maintained such that even when the catheter assembly is disconnected from the external processing system the patient s historical data can be later retrieved when the catheter assembly is reconnected to the same or another external processing system For this purpose the catheter assembly may further comprise a battery located in prox imity of the memory for providing power to the memory when the memory is not connected to the external process ing system In addition the calibration information and patient specific information are preferably encoded in accor dance with a proprietary code stored in the memory This proprietary code may then be read by the external processing system to determine whether the catheter assembly is sup plied by a particular manufacturer prior to conducting fur ther processing Preferably the proprietary code is a binary code stored in the memory and is accessed by the external processing system and used thereby to decode the encoded calibration information and encoded patient specific infor mation In preferred embodiments of the invention the catheter may be either an intra arterial catheter an intra venous catheter an intra chamber catheter an intra orifice catheter 10 15 25 35 45 55 65 6 an intra cavity catheter or an organ contact catheter On the other hand the memory of the invention may also be used in non catheter applications such as topically applied sen sors inc
53. tion or oximetry which requires the transmis sion of two or more appropriate wavelengths of light into the blood or tissue and the detection of light reflection absorbance Accordingly preferred embodiments of the invention will be described for use with such devices In particular the present invention relates to a device for gathering physiological data from a patient and supplying the gathered data to a processing system Preferably such a device in accordance with the invention comprises at least one transducer for directly measuring physiological param eters of the patient or measuring an amount of a parameter indicative of a physiological condition of the patient and a memory which resides at a predetermined location with respect to the at least one transducer Preferably the memory contains calibration information for calibrating the trans ducer and patient specific information which can be accessed by the processing system to which the device is connected for processing Preferably the memory is selected such that disconnection of the device from the processing system does not cause values stored in the memory to be lost so that the patient specific information need be rcentered into the memory when the device is reconnected to the same or another processing system Also in order to prevent piracy it is preferred that the stored data be encoded Preferably the device of the invention is a catheter assembly and the transducers ar
54. tor the filament tem perature so as to limit the peak filament temperature to a maximum of 52 C which corresponds to a peak surface temperature of about 48 C and an average surface tem perature of about 44 C depending upon the material composition and thickness For example in the event the heating filament temperature exceeds 52 C for more than say 15 seconds at full power the delivered heating filament power is reduced Then if the heating filament temperature exceeds 52 C for more than say 15 seconds at reduced power the heating filament power may be shut off and a panel alarm activated This prevents the peak surface tem perature from exceeding 48 C Moreover the average catheter surface temperature should not exceed 44 C since the power will be switched ON approximately 50 of the time Furthermore if the average cardiac output exceeds 3 5 liters minute the catheter s average surface temperature will generally remain below 44 C Thus regulation of power to the catheter only becomes an issue when the cardiac output becomes less than about 3 5 liters minute However since the power to the heating filament is reduced or shut off as the filament temperature reaches 52 C the heating element of the invention can be made relatively fail safe through closed loop control of the surface temperature By using a power source which is a constant voltage source an increasing catheter filament temperature can be dir
55. urther may be combined either directly or through the connector leads to any or all catheter transducers Furthermore the memory 102 may reside on a removable sensor probe that fits within a lumen of the catheter or may be included in the catheter or connector in such a way that it is accessible not directly by the external processing system but rather by means of one of the internal transducers Accordingly all such modifications are intended to be included within the scope of this invention as defined in the following claims We claim 1 A thermodilution catheter assembly for use in deter mining a patient s cardiac output comprising i a catheter adapted to be inserted into a patient s bloodstream said catheter having a heating filament made of a thin flexible material having a temperature coefficient of resistance of at least 0 001 ohms per ohm degree centigrade and 35 40 45 55 65 14 ii a memory which resides at a predetermined location on or about said catheter said memory storing ther modilution information comprising a heating filament calibration information said heat ing filament calibration information comprising 1 heating filament electrical resistance of said heating filament at a given temperature 2 heating filament heat transfer efficiency of said heating filament and 3 heating filament temperature coefficient of resis tance of said heating filament 2 The thermodilution cathet
56. wn where CS indicates chip select NC indicates no connection and ORG indicates memory organization As would be apparent to one skilled in the art although only one address or clock line is shown any number of lines can be used Also as shown in more detail in FIGS 3 and 4 the address and data lines preferably go to a connector 300 and these address and data lines may be shared with other transducer s lines which in the case illustrated are filament heater lines FIGS 3 5 illustrate in more detail the catheter connector 306 of the invention As shown the memory or chip 102 is mounted in the proximal end of the catheter at the connector 300 Connector pins 302 are attached to the pins of the memory chip 1 2 so as to allow the memory 102 to be accessed by an external processing device when the catheter connector 300 is plugged into the external processing device either directly or via a connecting cable The catheter assembly may further include a connector cover 400 as shown in FIGS 4 and 5 to protect the memory chip 1 102 from damage As noted above in a preferred embodiment of the inven tion the memory 102 is a CAT93C46 1 Kbit serial EEPROM A CAT93C46 memory device is organized in 64 registers of 16 bits ORG pin at VCC or 128 registers of 8 bits each ORG pin at GND Each register can be written or read serially by using the DI or DO pins The CAT93C46 memory device is desirable since it is a CMOS EEPROM with
Download Pdf Manuals
Related Search