Device for determining thoracic impedance

• US 20060135886A1
• Filed: 12/02/2005
• Published: 06/22/2006
• Est. Priority Date: 12/02/2004
• Status: Active Grant

• Current Assignee: Biotronik SE & Company KG
• Original Assignee: Biotronik VI Patent AG (Biotronik SE & Company KG)
• Inventors: Lippert, Michael, Czygan, Gerald
• Granted Patent: US 8,060,196 B2
• Time in Patent Office: Days
• US Class Current: 600/547
• CPC Class Codes: A61B 5/0031 Implanted circuitry
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content

Abstract

An electromedical implant includes a measuring signal generator, an impedance measuring unit to determine the impedance of human or animal tissue, a control unit which, for controlling the measuring signal generator and the impedance measuring unit, is at least indirectly connected to the measuring signal generator and to the impedance measuring unit, as well as an electrode arrangement comprising at least two electrodes which can be directly or indirectly connected or at least temporarily connected to the measuring signal generator and to the impedance measuring unit, or to a connection for such an electrode arrangement. The measuring signal generator is designed to generate and emit a current pulse or a series of current pulses, and the control unit is designed at a specific point in time to cause the measuring signal generator (to generate and emit a current pulse, and to cause the impedance measuring unit to measure the voltage that is present between the electrodes connected to the measuring signal generator and the impedance measuring unit after the passing of at least two time periods of different length that start with commencement of the current pulse being emitted and end before the end of emitting the current pulse, and to issue a voltage value which in each case represents the measured voltage.

Claims

1. An electromedical implant comprising:

a measuring signal generator;

an impedance measuring unit to determine the impedance of human or animal tissue;

a control unit which, for controlling the measuring signal generator and the impedance measuring unit, is at least indirectly connected to the measuring signal generator and the impedance measuring unit;

as well as an electrode arrangement comprising at least two electrodes which can be directly or indirectly connected or at least temporarily connected to the measuring signal generator and to the impedance measuring unit, or to a connection for such an electrode arrangement;

wherein;

the measuring signal generator is designed to generate and emit a current pulse or a series of current pulses;

and wherein the control unit is designed at a specific point in time to cause the measuring signal generator to generate and emit a current pulse;

and to cause the impedance measuring unit to measure the voltage that is present between the electrodes connected to the measuring signal generator and the impedance measuring unit after the passing of at least two time periods of different length that start with commencement of the current pulse being emitted and end before the end of emitting the current pulse, and to issue a voltage value which in each case represents the measured voltage.

2. The electromedical implant according to claim 1, wherein:

the control unit is designed to determine a value which represents a difference between the first and the last voltage value measured during emission of a current pulse emitted by the impedance measuring unit and to issue this difference as a voltage difference value.

3. The electromedical implant according to claim 2, wherein:

the control unit is designed to cause the impedance measuring unit to measure the voltage that is present between the electrodes that are connected to the measuring signal generator and to the impedance measuring unit after the passing of more than two time periods of different length that start with commencement of the current pulse being emitted and end before the end of emitting the current pulse, and to issue the voltage value measured in each case;

and wherein the control unit is designed

for each of the points in time, of causing a voltage reading to be taken depending on a first parameter U₀ and/or a second parameter τ

, to determine a multitude of compensating-curve values U_A which are calculated according to the formula

U_A=U₀*(1−

e<sup>−

t/τ</sup>

)

wherein e denotes Euler'"'"'s integral and t denotes the duration between first causing a voltage reading during the respective current pulse and the point in time of causing a voltage reading in relation to which the multitude of compensating-curve values U_A are to be determined;

in relation to a multitude of combinations of a value of the first parameter U₀ and/or a value of the second parameter X to determine the sum of the squares of the differences of all voltage values measured during the same current pulse, and of the compensating-curve value U_A calculated in relation to each voltage value according to the respective combination of a value of the first parameter U₀ and/or of a value of the second parameter τ

;

as well as by selecting the lowest sum to issue a combination of a value of the first parameter U₀ and/or of a value of the second parameter τ and

to issue it as a result parameter combination.

4. The electromedical implant according to claim 2, wherein:

the control unit is designed to cause the impedance measuring unit to measure the voltage that is present between the electrodes connected to the measuring signal generator and the impedance measuring unit after the passing of more than two time periods of different length that start with commencement of the current pulse being emitted and end before the end of emitting the current pulse, and to issue the voltage value measured in each case;

and that furthermore the control unit is designed to determine the coefficients of a polynomial which acts as a compensating curve, in relation to which polynomial the sum of the squares of the differences of all voltage values measured during the same current pulse and the values of the function of the polynomial for the points in time of causing a voltage reading is minimal, and to issue them as a result coefficient.

5. The electromedical implant according to claim 4, wherein:

the control unit is designed, as an increasing amount of time passes since commencement of emission of the current pulse that is being emitted by the measuring signal generator, after increased periods of time since the respective last causing of a voltage reading, to again cause the impedance measuring unit to measure the voltage present between the electrodes that are connected to the measuring signal generator and the impedance measuring unit.

6. The electromedical implant according to claim 5, wherein:

the control unit is designed to determine a value which represents a difference between the compensating-curve values U_A of the result parameter combination or the result coefficients for the durations t of the first and the last causing of a voltage reading, and to issue it as a voltage difference value.

13. The electromedical implant according to claim 2, wherein:

the measuring signal generator is designed to generate biphasal current pulses.

14. The electromedical implant according to claim 13, wherein:

the impedance measuring unit is designed to take impedance readings during emission of differently polarised segments of a biphasal current pulse through the measuring signal generator;

and wherein the control unit is designed to relate the values obtained in this way and to determine and issue a differential value obtained, which value represents a difference between two values obtained during emission of differently polarised segments of a biphasal current pulse.

7. An electromedical implant comprising at least

a measuring signal generator;

an impedance measuring unit to determine the impedance of human or animal tissue;

a control unit which, for controlling the measuring signal generator and the impedance measuring unit, is at least indirectly connected to the measuring signal generator ad the impedance measuring unit;

as well as an electrode arrangement comprising at least two electrodes which can be directly or indirectly connected or at least temporarily connected to the measuring signal generator and to the impedance measuring unit, or to a connection for such an electrode arrangement;

wherein;

the measuring signal generator is designed to generate and emit current pulses of variable pulse duration;

and wherein the control unit is designed at least at two different points in time to cause the measuring signal generator to generate and emit a current pulse, so that emission of the first current pulse is finished before emission of the second current pulse starts, and to differentiate between the pulse durations of the emitted current pulses;

and to cause the impedance measuring unit to measure the voltage that is present between the electrodes connected to the measuring signal generator and the impedance measuring unit at the beginning of a specific period of time that ends when emitting the respective current ends, and to issue it as a voltage value which represents the measured voltage.

8. The electromedical implant according to claim 7, wherein the control unit is designed to determine a value which represents a difference between the voltage values measured by the impedance measuring unit during two current pulses of different duration emitted by the measuring signal generator and to issue this difference as a voltage difference value.

9. The electromedical implant according to claim 8, wherein:

the control unit is designed to cause the measuring signal generator to generate and emit a current pulse at more than two different points in time so that emission of the first current pulse ends before emission of the second current pulse starts, and the pulse durations of the emitted current pulses differ from each other;

and to cause the impedance measuring unit to measure the voltage that is present between the electrodes that are connected to the measuring signal generator and to the impedance measuring unit at the beginning of a specific period of time that ends when emission of the respective current pulse ends;

and wherein furthermore, the control unit is designed, for each of the points in time of causing a voltage reading to be taken depending on a first parameter U₀ and/or a second parameter τ

, to determine a multitude of compensating-curve values U_A which are calculated according to the formula

U_A=U₀*(1−

e<sup>−

t/τ</sup>

)

wherein e denotes Euler'"'"'s integral and t denotes the duration between the point in time of commencement of emission of the current pulse, during which emission the control unit has caused the voltage reading, in relation to which the multitude of compensating-curve values U_A are to be determined, and the point in time of causing the voltage reading, in relation to which the multitude of compensating-curve values U_A are to be determined;

in relation to a multitude of combinations of a value of the first parameter U₀ and/or a value of the second parameter τ

to determine the sum of the squares of the differences of all voltage values measured during the more than two current pulses, and of the compensating-curve value U_A calculated in relation to each voltage value according to the respective combination of a value of the first parameter U₀ and/or of a value of the second parameter τ

;

as well as by selecting the lowest sum to issue a combination of a value of the first parameter U₀ and/or of a value of the second parameter τ and

to issue it as a result parameter combination.

10. The electromedical implant according to claim 8, wherein:

the control unit is designed at more than two different points in time to cause the measuring signal generator to generate and emit a current pulse so that emission of the first current pulse ends before commencement of emission of the second current pulse, and so that the pulse durations of the emitted current pulses differ from each other;

and to cause the impedance measuring unit to measure the voltage that is present between the electrodes that are connected to the measuring signal generator and the impedance measuring unit at the beginning of a specific period of time which ends when emission of the respective current pulse ends;

and wherein furthermore, the control unit is designed to determine the coefficients of a polynomial which acts as a compensating curve, in relation to which polynomial the sum of the squares of the differences of all voltage values measured during the more than two current pulses and the values of the function of the polynomial for the points in time of causing a voltage reading from the point in time of the beginning of emission of the respective current pulse is minimal, and to issue them as a result coefficient.

11. The electromedical implant according to claim 10, wherein:

the measuring signal generator is designed to generate current pulses of variable pulse duration, wherein the pulse duration is at least a first duration and at the longest a second duration;

and wherein the control unit is designed to cause the measuring signal generator to emit a larger number of current pulses of comparatively short pulse duration than of current pulses of comparatively longer pulse duration.

12. The electromedical implant according to claim 11, wherein:

the control unit is designed to determine a value that represents a difference between the compensating-curve values U_A of the result parameter combination or of the result coefficients in relation to the durations t of the current pulses with the longest and shortest pulse durations and to issue said value as a voltage difference value.

15. An electromedical implant comprising:

a measuring signal generator;

an impedance measuring unit to determine the impedance of human or animal tissue;

a control unit which, for controlling the measuring signal generator and the impedance measuring unit, is at least indirectly connected to the measuring signal generator and the impedance measuring unit;

as well as an electrode arrangement comprising at least two electrodes which are adjusted to be directly or indirectly connected, or at least temporarily connected, to the measuring signal generator and to the impedance measuring unit, or to a connection for such an electrode arrangement;

wherein;

the measuring signal generator is designed to generate and emit sinusoidal currents of at least two different frequencies;

and wherein the impedance measuring unit is designed to measure the amplitude of at least one sinusoidal voltage and/or the phase relationship between two sinusoidal voltages and to issue the value as a voltage value which represents the measured amplitude or the measured phase relationship or both.

16. The electromedical implant according to claim 15, wherein:

the control unit is designed, after a predefinable period of time, to cause the measuring signal generator to increase the frequency of the sinusoidal current generated and emitted by said measuring signal generator until such time as the impedance measuring unit detects and signals to the control unit a certain predefinable phase difference between the sinusoidal current and the voltage present at the electrodes that are connected to the impedance measuring unit.

17. The electromedical implant according to claim 16, wherein:

the control unit is designed to specify a period of time during which the phase difference that is measured by the impedance measuring unit is to be continually determined before the impedance measuring unit signals detection of the phase difference.

18. The electromedical implant according to claim 17, wherein:

the impedance measuring unit is designed to determine and issue the maximum and/or the minimum of the measured phase differences between the sinusoidal current and the voltage present at the electrodes that are connected to the impedance measuring unit.

19. The electromedical implant according to claim 18, wherein:

the impedance measuring unit is connected or adapted to be connected to at least one electrode by way of a filter;

wherein the filter, being a low-pass or band-pass filter, comprises a pass range which attenuates an input signal of the frequency of the sinusoidal current generated by the measuring signal generator as little as possible.

20. The electromedical implant according to claim 19, wherein:

the pass range of the filter is smaller than the difference between the highest and the lowest frequency of the sinusoidal currents generated by the measuring signal generator;

and wherein the cut-off frequencies of the filter are variable and can be predefined such that the frequencies of the sinusoidal currents that are generated by the measuring signal generator are within the filter'"'"'s pass range determined by the predefined cut-off frequencies.

21. The electromedical implant according to claim 20, wherein:

the electromedical implant comprises a subtracter which is connected to the impedance measuring unit and is designed to determine and issue as an amplitude differential value a value that represents a difference between at least two amplitudes determined by the impedance measuring unit in relation to sinusoidal currents of different frequencies.

22. The electromedical implant according to claim 21, wherein:

the measuring signal generator is designed to generate a sinusoidal current of a frequency of approximately 2 kHz and/or a sinusoidal current of a frequency of approximately 20 kHz.

23. The electromedical implant according to claim 22, wherein:

an amplifier is connected in series to the impedance measuring unit, which amplifier is designed to amplify or to reduce a voltage between an electrode connected to the measuring signal generator and an electrode indirectly connected to the impedance measuring unit, and to feed the resulting voltage to the impedance measuring unit,

wherein the amplification factor of the amplifier is variable.

24. The electromedical implant according to claim 23, wherein:

the amplification factor of the amplifier in operation can be adjusted such that the amount of the maximum value of the amplified voltage does not fall below a first voltage value and does not exceed a second voltage value.

25. The electromedical implant according to claim 24, wherein:

a subtracter unit is connected in series to the amplifier, wherein said subtracter unit is designed to deduct a predefined and settable voltage value from the voltage present at the subtracter unit and to feed the resulting voltage to the amplifier.

26. The electromedical implant according to claim 25, wherein:

the electromedical implant comprises more than two electrodes or can be connected to more than two electrodes;

and wherein the impedance measuring unit is designed to be connected to a selectable electrode and to a fixed or selectable electrode, and to measure a voltage that is present between these electrodes.

27. The electromedical implant according to claim 26, wherein:

the electromedical implant comprises more than two electrodes or can be connected to more than two electrodes;

and wherein the measuring signal generator is designed to be connected to a selectable electrode and a fixed or selectable electrode.

28. The electromedical implant according to claim 27, wherein:

the control unit is designed in relation to several different combinations of two electrodes that are connected or adapted to be connected with the impedance measuring unit and the measuring signal generator to emit a current pulse or a sinusoidal current, and to cause the impedance measuring unit to measure the voltage that is present between the respective combination of two electrodes and to calculate and issue an average value of the voltage values that have been determined in this way and that represent the measured voltages.

29. The electromedical implant according to claim 28, wherein:

the electromedical implant is a cardiac pacemaker, cardioverter or defibrillator.

30. The electromedical implant according to claim 29, wherein:

the electromedical implant comprises a cardiac activity detector which is designed to register the cardiac cycle of a patient and at a defined point in time within a cardiac cycle, to issue a signal to the control unit;

and wherein the control unit is designed, after receiving a signal from the cardiac activity detector, to cause the measuring signal generator to generate a current pulse or a measuring signal and to emit said current pulse or measuring signal by way of at least one electrode.

31. The electromedical implant according to claim 30, wherein:

the electromedical implant comprises a respiratory activity detector which is designed to register the respiratory cycle of a patient and at a defined point in time within a respiratory cycle to issue a signal to the control unit;

and wherein the control unit is designed, after receiving a signal from the cardiac activity detector, to cause the measuring signal generator to generate a current pulse or a measuring signal and to emit said current pulse or measuring signal by way of at least one electrode.

32. The electromedical implant according to claim 31, wherein:

the electromedical implant is designed to take series of impedance readings;

and wherein the control unit is designed to determine the average value of the readings obtained in a series of impedance readings and to issue it as a resulting value.

33. The electromedical implant according to claim 32, wherein:

the electromedical implant is designed to take series of impedance readings;

and wherein the control unit is designed to determine the median of the readings obtained in a series of impedance readings and to issue it as a resulting value.

34. The electromedical implant according to claim 33, wherein:

the electromedical implant comprises a wireless data transmission interface;

and wherein the wireless data transmission interface is designed to transmit to a home monitoring service center one or several of the parameters, determined or issued by the control unit, such as the voltage difference value, average value, value of the first parameter U₀, value of the second parameter τ and

amplitude difference value and/or one or several of the voltage values or amplitude values determined by the impedance measuring unit, by way of the wireless data transmission interface directly or indirectly as patient data.

35. A system comprising at least

an electromedical implant according to claim 34

and at least one of a patient device and a home monitoring service center;

wherein the electromedical implant and the patient device can be connected to each other by way of wireless data transmission interfaces, and the patient device and the home monitoring service center can be connected to each other by way of a wireless or a wire-bound data transmission interface.

36. The system according to claim 35, wherein:

the patient device or the home monitoring service center is designed to store the patient data received by the electromedical implant and to calculate short-term and long-term average values of individual patient data.

37. The system according to claim 36, wherein:

the patient device or the home monitoring service centre are designed to compare received patient data with the calculated short-term and long-term average values.

38. The system according to claim 37, wherein:

the patient device or the home monitoring service centre are designed to display any deviations between the short-term and long-term average values and the patient data compared with the short-term and long-term average values.