Source: http://www.google.com/patents/US6695790?dq=6778979
Timestamp: 2017-06-23 19:30:21
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Matched Legal Cases: ['art 8', 'art 8', 'art 8', 'art 8', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100', 'art 100']

Patent US6695790 - Method and system for determining kidney failure - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inPatentsA method of determining kidney failure in a patient using an implantable medical device is described. In one embodiment, a first magnitude of a first polarization signal is measured. An additional magnitude of an additional polarization signal is measured after a first interval. A deflection differential...http://www.google.com/patents/US6695790?utm_source=gb-gplus-sharePatent US6695790 - Method and system for determining kidney failureAdvanced Patent SearchTry the new Google Patents, with machine-classified Google Scholar results, and Japanese and South Korean patents.Publication numberUS6695790 B2Publication typeGrantApplication numberUS 09/984,087Publication dateFeb 24, 2004Filing dateOct 26, 2001Priority dateOct 26, 2001Fee statusPaidAlso published asUS20030083585Publication number09984087, 984087, US 6695790 B2, US 6695790B2, US-B2-6695790, US6695790 B2, US6695790B2InventorsGeeske van Oort, Jos W. J. Van HoveOriginal AssigneeMedtronic, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (31), Non-Patent Citations (2), Referenced by (7), Classifications (8), Legal Events (4) External Links: USPTO, USPTO Assignment, EspacenetMethod and system for determining kidney failure
US 6695790 B2Abstract
A method of determining kidney failure in a patient using an implantable medical device is described. In one embodiment, a first magnitude of a first polarization signal is measured. An additional magnitude of an additional polarization signal is measured after a first interval. A deflection differential between the first magnitude and the additional magnitude is determined and kidney failure in the patient is determined when the deflection differential is greater than an established threshold.
We claim: 1. A method for determining kidney failure in a patient using an implantable medical device, the method comprising:
measuring a first magnitude of a first polarization signal; measuring an additional magnitude of an additional polarization signal after a first interval; determining a deflection differential between the first magnitude and the additional magnitude; and determining whether a patient is likely to be experiencing or to experience kidney failure when the deflection differential is greater than an established threshold. 2. The method of claim 1, further comprising measuring the first magnitude of the first polarization signal during a first visit of the patient for a dialysis treatment.
3. The method of claim 2, further comprising measuring the additional magnitude of the second polarization signal during an additional visit of the patient for the dialysis treatment.
4. The method of claim 1, further comprising pacing a cardiac tissue of the patient with the implantable medical device.
5. The method of claim 4, further comprising monitoring a heart rate.
6. The method of claim 1, further comprising determining the established threshold.
7. The method of claim 1, further comprising comparing the deflection differential to a plurality of differential values to determine the established threshold.
8. The method of claim 1, further comprising setting the established threshold at a predetermined value based on a patient history.
9. The method of claim 1, further comprising storing in a memory at least one established threshold value.
10. The method of claim 1, further comprising storing the first magnitude in a memory.
11. The method of claim 1, further comprising storing the additional magnitude in a memory.
12. A method of determining kidney failure using a pacing system, the pacing system comprising at least one medical electrical lead having at least one first electrode configured for positioning in a cardiac tissue of a patient, an implantable pulse generator operably connected to the at least one medical electrical lead, and means for measuring a magnitude of a polarization signal, the method comprising:
measuring a first magnitude of a first polarization signal; measuring an additional magnitude of an additional polarization signal after a first interval; determining a deflection differential between the first magnitude and the additional magnitude; and determining a kidney failure in the patient when the deflection differential is greater than an established threshold. 13. The method of claim 12, further comprising measuring the first magnitude of the first polarization signal during a first visit of the patient for a dialysis treatment.
14. The method of claim 13, further comprising measuring the additional magnitude of the second polarization signal during an additional visit of the patient for the dialysis treatment.
15. The method of claim 12, further comprising pacing the cardiac tissue of the patient with the implantable medical device.
16. The method of claim 15, further comprising monitoring a heart rate.
17. The method of claim 12, further comprising determining the established threshold.
18. The method of claim 12, further comprising comparing the deflection differential to a plurality of differential values to determine the established threshold.
19. The method of claim 12, further comprising setting the established threshold at a predetermined value based on a patient history.
20. The method of claim 12, further comprising storing at least one established threshold value in a computer memory.
21. The method of claim 12, further comprising storing the first magnitude in a computer memory.
22. The method of claim 12, further comprising storing the additional magnitude in a computer memory.
23. An implantable medical device for determining kidney failure in a patient, said device comprising:
at least one sensor lead operable to sense at least one polarization signal; a processor operatively coupled to said at least one sensor lead; wherein said processor is operable to measure a first magnitude of a first polarization signal during a first visit of the patient for a dialysis treatment; wherein said processor is further operable to measure a second magnitude of a second polarization signal during a second visit of the patient for a dialysis treatment; wherein said processor is further operable to determine a deflection differential between the first magnitude and the second magnitude; and wherein said processor is further operable to determine a kidney failure in the patient when the deflection differential is greater than an established threshold. 24. The device of claim 23, further comprising:
at least one pacing lead operable to pace the cardiac tissue of the patient. 25. The device of claim 24 wherein the processor is further operable to monitor a heart rate of the cardiac tissue.
26. The device of claim 24 wherein the processor is further operable to determine the established threshold.
27. The device of claim 24 further comprising a database comprising a plurality of differential values, wherein the processor is further operable to determine the established threshold by comparing the deflection differential to the differential values.
28. The device of claim 23 wherein the processor is further operable to set the established threshold at a predetermined value based on a patient history.
29. The device of claim 23, further comprising a storage location for storing at least one established threshold value.
30. The device of claim 23, further comprising a storage location for storing the first magnitude.
31. The device of claim 23, further comprising a storage location for storing the second magnitude.
an implantable pulse generator; at least one medical electrical lead operably connected to the implantable pulse generator, the medical electrical lead having at least one first electrode configured for positioning in a cardiac tissue of a patient; and a processor operably adapted to measure a first magnitude of a first polarization signal in the cardiac tissue of the patient and to measure an additional magnitude of an additional polarization signal after a first interval; the processor further operably adapted to determine a deflection differential between the first magnitude and the additional magnitude; and to determine a kidney failure in the patient when the deflection differential is greater than an established threshold. 33. The device of claim 32, further comprising at least one pacing lead operably adapted to pace the cardiac tissue of the patient.
34. The device of claim 32, wherein the processor is further operably adapted to monitor a heart rate of the cardiac tissue.
35. The device of claim 32, wherein the processor is further operably adapted to determine the established threshold.
36. The device of claim 32, further comprising a database comprising a plurality of differential values, wherein the processor is further operably adapted to determine the established threshold by comparing the deflection differential to the differential values.
37. The device of claim 32, wherein the processor is further operably adapted to set the established threshold at a predetermined value based on a patient history.
38. The device of claim 32, further comprising a memory location operably connected to the processor for storing at least one established threshold value.
39. The device of claim 32, further comprising a memory location operably connected to the processor for storing the first magnitude.
40. The device of claim 32, further comprising a memory location operably connected to the processor for storing the second magnitude.
41. An implantable medical system for determining kidney failure in a patient, the system comprising:
at least one medical electrical lead having at least one first electrode configured for positioning in a cardiac tissue of the patient; an implantable pulse generator operably connected to the at least one medical electrical lead; means for measuring a first magnitude of a first polarization signal; means for measuring an additional magnitude of an additional polarization signal after a first interval; means for determining a deflection differential between the first magnitude and the additional magnitude; and means for determining a kidney failure in the patient when the deflection differential is greater than an established threshold. 42. The system of claim 41, further comprising means for measuring the first magnitude of the first polarization signal during a first visit of the patient for a dialysis treatment.
43. The system of claim 41, further comprising means for measuring the additional magnitude of the second polarization signal during an additional visit of the patient for the dialysis treatment.
44. The system of claim 41, further comprising means for pacing the cardiac tissue of the patient.
45. The system of claim 41, further comprising means for monitoring a heart rate of the cardiac tissue.
46. The system of claim 41, further comprising means for determining the established threshold.
47. The system of claim 41, further comprising means for comparing the deflection differential to a plurality of differential values to determine the established threshold.
48. The system of claim 41, further comprising means for setting the established threshold at a predetermined value based on a patient history.
49. The system of claim 41, further comprising means for storing at least one established threshold value.
50. The system of claim 41, further comprising means for storing the first magnitude.
51. The system of claim 41, further comprising means for storing the additional magnitude.
52. System means for implementing a computer useable medium including a computer program for determining kidney failure in a patient using a pacing system, the pacing system comprising at least one medical electrical lead having at least one first electrode configured for positioning in a cardiac tissue of a patient, an implantable pulse generator operably connected to the at least one medical electrical lead, and means for measuring a magnitude of a polarization signal, the system implementing means comprising:
means for implementing computer program code that measures a first magnitude of a first polarization signal; means for implementing computer program code that measures an additional magnitude of an additional polarization signal after a first interval; means for implementing computer program code that determines a deflection differential between the first magnitude and the additional magnitude; and means for implementing computer program code that determines a kidney failure in the patient when the deflection differential is greater than an established threshold. 53. The program of claim 52, further comprising means for implementing computer program code that measures the first magnitude of the first polarization signal during a first visit of the patient for a dialysis treatment.
54. The program of claim 52, further comprising means for implementing computer program code that measures the additional magnitude of the second polarization signal during an additional visit of the patient for the dialysis treatment.
55. The program of claim 52, further comprising means for implementing computer program code that paces the cardiac tissue of the patient.
56. The program of claim 52, further comprising means for implementing computer program code that monitors a heart rate of the cardiac tissue.
57. The program of claim 52, further comprising means for implementing computer program code that determines the established threshold.
58. The program of claim 52, further comprising means for implementing computer program code that compares the deflection differential to a plurality of differential values to determine the established threshold.
59. The program of claim 52, further comprising means for implementing computer program code that sets the established threshold at a predetermined value based on a patient history.
60. The program of claim 52, further comprising means for implementing computer program code that stores at least one established threshold value.
61. The program of claim 52, further comprising means for implementing computer program code that stores the first magnitude.
62. The program of claim 52, further comprising means for implementing computer program code that stores the additional magnitude.
The present invention relates to the field of implantable medical devices. More particularly, the present invention relates to cardiac pacing systems that are capable of measure and compare polarization signals to thereby determine an occurrence of a kidney failure.
Implantable pulse generators (or IPGS) are well known in the prior art. After a stimulus in the heart, a charge builds up at the electrode tip, which results in a polarization signal that decays over time. While an initial magnitude of the polarization signal is dependent upon the configuration of the electrode as well as any fibrosis around the electrode tip, ionic concentration in the blood ambient the heart is a major factor in the generation of the initial magnitude. For a patient having a significant risk of experiencing kidney failure, the ionic concentration may increase with each succeeding dialysis of the patient. However, the medical arts have failed to utilize various measurements of the polarization signal to ascertain any increases in the ionic concentration with each succeeding dialysis of the patient.
Thus, prior to the present invention, a need existed in the medical arts for facilitating a determination of a kidney failure by a patient.
Several methods have been proposed in the prior art for to determine various concentrations within the heart of a patient.
For example, U.S. Pat. No. 4,716,887 to Koning et al., entitled “Apparatus And Method For Adjusting Heart/Pacer Rate Relative To Cardiac PCO2 To Obtain A Required Cardiac Output,” hereby incorporated by reference in its entirety, discloses pacing pulses to the right ventricle of the heart and a pCO2 sensor for sensing pCO2 of the blood in the heart. A microprocessor is programmed to relate the pCO2 with the required heart rate or change in rate, •R, needed to supply a desired cardiac output and to cause the pacer to pace the heart at the required heart rate when the heart is not naturally paced.
U.S. Pat. No. 4,705,494 to King, entitled “Automatic Implantable Fibrillation Preventer,” hereby incorporated by reference in its entirety, discloses a dual sensing of the probable onset of ventricular fibrillation or other harmful tachyarrythmias and delivering electrical cardioverting stimulation pulses in response thereto. One sensing technique utilizes an intracardiac ECG observed within three dimensional space. The other sensing technique employs a chemically sensitive semiconductor device which measures the level of ionic potassium found within the intracardiac blood.
U.S. Pat. No. 4,899,750 to Ekwall. entitled “Lead Impedance Scanning System For Pacemakers”, hereby incorporated by reference in its entirety, discloses making separate measurements of lead impedance during each heart signal and each pacing pulse. A moving average of measures parameters is maintained and recurring deviations from the norms are noted in separate event counters for subsequent analysis of the noted events as possible indications of impending failure of an implanted lead.
US 4,716,887
US 4,750,494
Jun. 14, 1988
US 4,899,750
The present invention is therefore directed to providing a method and system for managing therapies in a cardiac pacing system. Such a system of the present invention overcomes the problems, disadvantages and limitations of the prior art described above, and provides a more efficient and accurate means of determining kidney failure in a patient.
The present invention has certain objects. That is, various embodiments of the present invention provide solutions to one or more problems existing in the prior art respecting the determination of kidney failure in a patient. Those problems include, without limitation: the lack of knowledge relating to an interpretation of any deflections in a polarization signal as an indication of kidney failure; inability to use ambient heart conditions as indication of kidney failure; inability to track likelihood of kidney failure with succeeding dialysis sessions; inability to determine risk of kidney failure using measurements of the polarization signal; and inability to correlate polarization signal magnitude with potential kidney failure.
In comparison to known techniques for determining kidney failure, various embodiments of the present invention may provide the following advantages, interalia, i.e., use of an implantable medical device in determining an occurrence of kidney failure in a patient; ability to determine ionic concentration in the blood ambient the heart; ability to correlate ionic concentration in the blood with magnitude of a polarization signal; ability to measure potential risk of kidney failure with each succeeding dialysis based on ionic concentration; ability to correlate risk of kidney failure with polarization signals measured by an implantable medical device; and use of one implantable medical device to provide pacing stimulation and concomitantly, to measure potential kidney failure.
Some embodiments of the present invention include one or more of the following features: (a) an IPG capable of measuring ionic concentration in the blood; (b) an IPG capable of determining magnitudes of polarization signals; (c) an IPG capable of correlating ionic concentration with magnitudes of polarization signals; (d) an IPG capable of determining potential kidney failure based on ambient heart conditions; (e) an IPG capable of correlating polarization signals with risk of kidney failure over a period of time (f) methods of determining potential kidney failure based on ambient heart conditions; and (g) methods of correlating magnitudes of polarization signals with risk of kidney failure over time.
At least some embodiments of the invention provide methods for determining kidney failure, such as: (a) a first magnitude of a first polarization signal being determined during a first visit of the patient for a dialysis treatment, a second magnitude of a second polarization signal being determined during a second visit of the patient for a dialysis treatment, and a deflection differential between the first magnitude and the second magnitude being determined and the probability or existence of kidney failure being determined for the patient when the deflection differential exceeds or is greater than an established threshold; (b) a series of discrete and individual historical or chronological polarization signal trends being calculated by comparing a series of presently measured polarization signals respecting previously measured polarization signals, where the polarization trend signals are calculated and stored in memory at predetermined intervals for subsequent retrieval or signal processing; (c) discrete or individual polarization trend signals being employed to alert or warn the patient or a health care professional that the patient has a probability of or is experiencing kidney failure in response to a predetermined polarization trend signal threshold being reached or exceeded; (d) a warning or alert being provided to a remote health care provider through internet or telephonic communication between the implantable medical device and a remote computer, server or database; (e) in response to a warning or alert being generated, the patient and/or health care provider being prompted to arrange dialysis treatment for the patient within a specified time period.
FIG. 1 is a schematic view of an implantable medical device in situ, made in accordance with one embodiment of the present invention;
FIG. 2 is a schematic view of one embodiment of the implantable medical device of FIG. 1, made in accordance with one embodiment of the present invention;
FIG. 3 is a block diagram illustrating components of an embodiment of the implantable medical device of FIG. 1, made in accordance with one embodiment of the present invention;
FIG. 4 is a schematic view of another embodiment of an implantable medical device, made in accordance with one embodiment of the present invention;
FIG. 5 is a block diagram illustrating components of an embodiment of the implantable medical device of FIG. 4, made in accordance with one embodiment of the present invention;
FIG. 6 is a schematic view of another embodiment of an implantable medical device, made in accordance with one embodiment of the present invention;
FIG. 7 is a flowchart of a kidney failure detection method as implemented by the implantable medical devices of any one or more of FIGS. 1-6 in accordance with the present invention; and
FIG. 8 is a graph of various polarization signals as measured by any one or more of the implantable medical devices of FIGS. 1-6.
FIG. 1 is a simplified schematic view of one embodiment of implantable medical device (“IMD”) 10 of the present invention. The IMD 10 shown in FIG. 1 is a pacemaker comprising at least one of pacing and sensing leads 16 and 18. Leads 16, 18 may be attached to hermetically sealed enclosure 14 and may be implanted near human or mammalian heart 8. Pacing lead 16 and sensing lead 18 may sense electrical signals attendant to the depolarization and re-polarization of the heart 8, and further provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof. Leads 16 and 18 may have unipolar or bipolar electrodes disposed thereon, as is well known in the art. Examples of IMD 10 include implantable cardiac pacemakers disclosed in U.S. Pat. No. 5,158,078 to Bennett et al., U.S. Pat. No. 5,312,453 to Shelton et al. or U.S. Pat. No. 5,144,949 to Olson, all of which are hereby incorporated by reference, each in its respective entirety.
During pacing, escape interval counters within pacer timing/control circuitry 63 are reset upon sensing of R-waves and P-waves as indicated by signals on lines 39 and 45, and in accordance with the selected mode of pacing on time-out trigger generation of pacing pulses by pacer output circuitry 65 and 67, which are coupled to electrodes 9, 13, 2 and 3. Escape interval counters are also reset on the generation of pacing pulses and thereby control the basic timing of cardiac pacing functions, including anti-tachyarrhythmia pacing. The durations of the intervals defined by escape interval timers are determined by microprocessor 51 via data/address bus 53. The value of the count present in the escape interval counters when reset by sensed R-waves and P-waves may be used to measure the durations of R—R intervals, P—P intervals, P-R intervals and R-P intervals, which measurements are stored in memory 59 and used to detect the presence of tachyarrhythmias.
Detection of atrial or ventricular tachyarrhythmias, as employed in the present invention, may correspond to any of the various tachyarrhythmia detection algorithms presently known in the art. For example, the presence of an atrial or ventricular tachyarrhythmia may be confirmed by detecting a sustained series of short R—R or P—P intervals of an average rate indicative of tachyarrhythmia or an unbroken series of short R—R or P—P intervals. The suddenness of onset of the detected high rates, the stability of the high rates, and a number of other factors known in the art may also be measured at this time. Appropriate ventricular tachyarrhythmia detection methodologies measuring such factors are described in U.S. Pat. No. 4,726,380 issued to Vollmann, U.S. Pat. No. 4,880,005, issued to Pless et al. and U.S. Pat. No. 4,830,006, issued to Haluska et al., all hereby incorporated by reference, each in their respective entirety. An additional set of tachycardia recognition methodologies is disclosed in the article “Onset and Stability for Ventricular Tachyarrhythmia Detection in an Implantable Pacer-Cardioverter-Defibrillator” by Olson et al., published in Computers in Cardiology, Oct. 7-10, 1986, IEEE Computer Society Press, pp. 167-170, also hereby incorporated by reference in its entirety. Atrial fibrillation detection methodologies are disclosed in published PCT Application Ser. No. US92/02829, Publication No. WO92/18198, by Adams et al., and in the article “Automatic Tachycardia Recognition”, by Arzbaecher et al., published in PACE, May-June, 1984, pp. 541-547, both of which are hereby incorporated by reference in their entireties.
In the event that the generation of a cardioversion or defibrillation pulse is required, microprocessor 51 may employ an atrial escape interval counter to control timing of such cardioversion and defibrillation pulses, as well as the associated refractory periods. In response to the detection of atrial or ventricular fibrillation or tachyarrhythmia requiring a cardioversion pulse, microprocessor 51 activates cardioversion/defibrillation control circuitry 29, which initiates charging of the high voltage capacitors 33 and 35 via charging circuit 69, under the control of high voltage charging control line 71. The voltage on the high voltage capacitors is monitored via VCAP line 73, which is passed through multiplexer 55 and in response to reaching a predetermined value set by microprocessor 51, results in generation of a logic signal on Cap Full (CF) line 77 to terminate charging. Thereafter, timing of the delivery of the defibrillation or cardioversion pulse is controlled by pacer timing/control circuitry 63. Following delivery of the fibrillation or tachycardia therapy, microprocessor 51 returns the device to a cardiac pacing mode and awaits the next successive interrupt due to pacing or the occurrence of a sensed atrial or ventricular depolarization.
FIG. 6 is a simplified schematic view of one embodiment of implantable medical device (“IMD”) 10 of the present invention. The IMD 10 shown in FIG. 6 is a pacemaker comprising at least one of pacing and sensing leads 16 and 18. Leads 16, 18 may be attached to hermetically sealed enclosure 14 and may be implanted near human or mammalian heart 8. Pacing lead 16 and sensing lead 18 may sense electrical signals attendant to the depolarization and re-polarization of the heart 8, and further provide pacing pulses for causing depolarization of cardiac tissue in the vicinity of the distal ends thereof. One or more of leads 16, 18 may be used to sense polarization signals in accordance with the present invention. Leads 16, 18 may be in communication with microprocessor 51. In one embodiment of the invention, microprocessor 51 may be used to measure the magnitudes of polarizations signals sensed by one or more of leads 16, 18. Microprocessor 51 may also be able to determine a deflection differential between various magnitudes measured over time. For example, a polarization signal may be sensed during a first instance by leads 16, 18, processed by processor 51 and stored in a memory or a portion of memory of IMD 10. Such memory may be, by way of example only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed and consequently executed by microprocessor 51/microcomputer 58.
A subsequent polarization signal may then be sensed at a later time by leads 16, 18 and processed. This subsequent polarization signal may then be compared to the first stored polarization signal. For example, microprocessor 51 may compare the two values and, if the deflection differential of the two values is greater than an established threshold, it may be determined that the patient may be in danger of kidney failure or may already have experienced kidney failure.
The established threshold may be one or a plurality of values stored within a memory of microprocessor 51. Such memory may be, by way of example only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed and consequently executed by microprocessor 51/microcomputer 58. For example, in one embodiment of the invention, the established threshold may be determined with reference to a database comprising a plurality of differential values. These differential values may be determined, for example, based on the patient's history or based on clinical results. Alternatively, the differential values may be set by the physician based on the patient's history or other physician-determined factors.
In other embodiments and methods of the present invention, a series of discrete and individual historical or chronological polarization signal trends may be calculated by comparing a series of presently measured polarization signals respecting previously measured polarization signals, where the polarization trend signals are calculated and stored in memory at predetermined intervals for subsequent retrieval or signal processing. Discrete or individual polarization trend signals may also be employed to alert or warn the patient or a health care professional that the patient has a probability of or is experiencing kidney failure in response to a predetermined polarization trend signal threshold being reached or exceeded. A warning or alert may be provided to a remote health care provider through internet or telephonic communication between the implantable medical device and a remote computer, server or database. In response to a warning or alert being generated, the patient and/or health care provider being prompted to arrange dialysis treatment for the patient within a specified time period. In the above respects, the teachings of PCT Patent Application Serial No. US01/01639 entitled “System and Method of Communicating between an Implantable Medical Device and a Remote Computer System or Health Care Provider” to Haller et al. may be employed to great advantage in respect of the present invention. The entirety of the foregoing PCT patent application to Haller et al. is hereby incorporated by reference herein.
Leads 16 and 18 may have unipolar or bipolar electrodes disposed thereon, as is well known in the art. Any one or more of the electrodes disposed on leads 16, 18 may be used to sense polarization values in accordance with the present invention. Examples of IMD 10 include implantable cardiac pacemakers disclosed in U.S. Pat. No. 5,158,078 to Bennett et al., U.S. Pat. No. 5,312,453 to Shelton et al. or U.S. Pat. No. 5,144,949 to Olson, all of which are hereby incorporated by reference, each in its respective entirety.
FIG. 7 illustrates a flowchart 100 of a kidney failure detection method of the present invention. The description herein of flowchart 100 is based upon a utilization of IMD 10, but those having ordinary skill in the art will appreciates the applicability of flowchart 100 to various types of implantable medical devices. During a stage S102 of flowchart 100, a measurement by IMD 10 of a polarization signal is obtained during a visit by a patient carrying IMD 10 to a hospital or clinic for a first dialysis treatment. Alternatively, the polarization signal may be sensed by leads 16, 18 at any time after IMD 10 has been implanted in the patient. The magnitude of the sensed polarization signal may then be stored as described above for later comparison. Storage of the magnitude value may be performed automatically, for example by a computer algorithm and/or program capable of being stored in an electronic medium such as, by way of example only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed and consequently executed by microprocessor 64/microcomputer 58. Alternatively, a physician may manually cause storage of the magnitude value.
FIG. 8 illustrates a polarization signal PS1 that is representative of polarization signal obtained during stage S102. During a stage S104 of flowchart 100, a measurement by IMD 10 of a polarization signal is obtained during a subsequent visit by the patient carrying IMD 10 to a hospital or clinic for a second dialysis treatment. Alternatively, the subsequent polarization signal may be sensed by leads 16, 18 at any time after IMD 10 has been implanted in the patient. The magnitude of the subsequent sensed polarization signal may then be stored as described above for later comparison to the first sensed polarization signal. Storage of the magnitude value may be performed automatically, for example by a computer algorithm and/or program capable of being stored in an electronic medium such as, by way of example only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed and consequently executed by microprocessor 64/microcomputer 58. Alternatively, a physician may manually cause storage of the magnitude value.
FIG. 8 illustrates a polarization signal PS2 and a polarization signal PS3 whereby each signal can serve as representation of the polarization signal obtained during stage S104.
During a stage S106 of flowchart 100, a deflection differential between the measured polarization signals is determined. For example, a deflection differential dv/dt1 is determined during stage S106 when polarization signal PS2 is the measured polarization during stage S104, and a deflection differential dv/dt2 is determined during stage S106 when polarization signal PS3 is the measured polarization during stage S104. During a stage S108 of flowchart 100, it is determined in the deflection differential determined during stage S106 is greater than a threshold level.
In one embodiment of the invention, microprocessor 51 may be used to determine a deflection differential between various magnitudes measured over time. For example, microprocessor 51 may compare the magnitude value of the first sensed polarization signal to the magnitude value of the subsequent sensed polarization signal. The physician may invoke processing of the deflection differential manually or, alternatively, comparison of polarization signal magnitudes and deflection differential calculations may be automatically performed.
Flowchart 100 terminates when the deflection differential is determined to be less than a threshold level during stage S108. Otherwise, an indication of kidney failure is provided during a stage S110 of flowchart 100 when the deflection differential is determined to be greater than a threshold level during stage S108. For example, deflection differential dv/dt1 can be less than the threshold level whereby no indication of kidney failure is provided, while deflection differential dv/dt2 can be greater than the threshold whereby an indication of kidney failure is provided. In one embodiment of the invention, microprocessor 51 may compare the two values and, if the deflection differential of the two values is greater than an established threshold, it may be determined that the patient may be in danger of kidney failure or may already have experienced kidney failure. The established threshold may be one or a plurality of values stored within a memory of microprocessor 51. Such memory may be, by way of example only, RAM 68 or ROM 70 of IMD 10, where the contents of RAM 68 and ROM 70 may be accessed and consequently executed by microprocessor 51/microcomputer 58. For example, in one embodiment of the invention, the established threshold may be determined with reference to a database comprising a plurality of differential values. These differential values may be determined, for example, based on the patient's history or based on clinical results. Alternatively, the differential values may be set by the physician based on the patient's history or other physician-determined factors.
There are various ways in which the various stages of flowchart 100 may be implemented in IMD 10. In one embodiment, a doctor can establish a connection of IMD 10 to a computer whereby the polarization signals are graphically displayed. The doctor can thereby detect any kidney failures by a visual interpretation of the graphical display. Alternatively, IMD 10 can provide an indication of kidney failure when applicable within the graphical display. In a second embodiment, a memory of IMD 10 can store various measurements of polarization signals and provide an audible sound upon a detection of kidney failure.
In the embodiment of the invention seen in FIGS. 1 through 7, the parameters determined include: a first polarization signal magnitude, a second polarization signal magnitude, a deflection value and a potential risk of kidney failure value. One or any suitable combination of these parameters may be varied in accordance with the present invention. Alternatively, one or more of these parameters may be set at a desired value while one or more other parameters are varied in accordance with the present invention. Moreover, although the parameters are shown as being determined in a given order, these parameters may be determined in any combination and in any order in accordance with the present invention.
In preferred embodiments of the present invention, the one or more electrodes employed to stimulate and produce the polarization signal on the basis of which a measure of kidney failure is derived, are special, dedicated electrodes configured for the sole purpose of measuring polarization signals or portions of such signals which lend themselves most readily to a determination of kidney failure. Accordingly, the stimulus of the present invention may be a pacing pulse (such as a pulse intended to cause contraction of heart tissue or a pulse delivered during the refractory period), or a pulse delivered in blood only so as to derive an appropriate measure of ionic concentration. The polarization signal so produced is preferably measured using DSP technology and processing techniques such as those described in U.S. Pat. No. 6,029,087 to Wohigemuth entitled “Cardiac Pacing System with Improved Physiological Event Classification Based on DSP.” Employment of a DSP to sense and process polarization signals in accordance with some embodiments of the present invention provides the further advantage of permitting polarization signal voltages to be measured “directly,” as opposed to measuring such signals using complicated analog circuit amplifier circuits as described hereinabove.
The preceding specific embodiments are illustrative of the practice of the invention. It is to be understood, therefore, that other expedients known to those skilled in the art or disclosed herein, may be employed without departing from the invention or the scope of the appended claims. For example, the present invention is not limited to a method for increasing determining the potential of kidney failure based on ambient heart conditions such as ionic concentration. The present invention is also not limited to the measurement of polarization signals, perse, but may find further application as a measuring means. The present invention further includes within its scope methods of making and using the measurement means described hereinabove.
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