Electrode impedance measurement

• US 10,368,805 B2
• Filed: 12/29/2016
• Issued: 08/06/2019
• Est. Priority Date: 12/29/2016
• Status: Active Grant

• Current Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Original Assignee: Dragerwerk AG & Company KGaA (FPS Vermögensverwaltung GmbH)
• Inventors: Qin, Derek Y.
• Primary Examiner(s): Mahmood, Nadia A
• Application Number:
  US15/394,349
• Publication Number:
  US 20180184980A1
• Time in Patent Office: 950 Days
• Field of Search: 600509
• CPC Class Codes: A61B 2562/0214 Capacitive electrodes
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/053 Measuring electrical impedance or conductance of a portion of the body
• CPC Class Codes: A61B 5/2415 Measuring direct current [DC] or slowly varying biopotentials
• CPC Class Codes: A61B 5/259 using conductive adhesive means, e.g. gels
• CPC Class Codes: A61B 5/303 Patient cord assembly, e.g. cable harness
• CPC Class Codes: A61B 5/6843 Monitoring or controlling sensor contact pressure

Abstract

Systems and methods are provided herein for monitoring electrocardiogram (ECG) electrodes. Each ECG electrode is electrically connected to a patient body and a corresponding current source. A reference ECG electrode of the monitored ECG electrodes is selected. Current is injected into each electrode. Each current has a respective predetermined level. Based on the injected currents, ECG electrode voltages are generated. The injected currents are adjusted after measuring the ECG electrode voltages while the predetermined level through the reference ECG electrode is maintained. An impedance associated with each non-reference ECG electrode is determined based on the ECG electrode voltage and the injected current.

Claims

1. A method implemented by one or more data processors forming part of at least one computing device, the method comprising:

monitoring, by at least one data processor of a computing device, electrocardiogram (ECG) electrodes each electrically connected to a patient body and a corresponding current source;

injecting, by the at least one data processor, one of a plurality of currents, each current having a respective predetermined level, into each ECG electrode;

measuring, by the at least one data processor, a plurality of ECG electrode voltages generated by the plurality of currents;

selecting, by the at least one data processor, a first reference ECG electrode from the monitored ECG electrodes, wherein unselected ECG electrodes include a plurality of non-reference ECG electrodes and a neutral drive electrode;

adjusting, by the at least one data processor, the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the predetermined level through the first reference ECG electrode; and

determining, by the at least one data processor, a plurality of impedances, each impedance corresponding to each non-reference ECG electrode, based on the plurality of ECG electrode voltages and the plurality of currents.

2. The method according to claim 1, further comprising:

selecting, by the at least one data processor, a second reference ECG electrode from the plurality of non-reference ECG electrodes;

adjusting, by the at least one data processor, the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the predetermined level through the second reference ECG electrode; and

determining, by the at least one data processor, impedances corresponding to the first reference ECG electrode and the neutral drive electrode based on the plurality of ECG electrode voltages and the plurality of currents.

3. The method according to claim 1, wherein each ECG electrode is modeled by an offset voltage and a resistor.

4. The method according to claim 3, wherein determining the plurality of impedances comprises:

generating, by the at least one data processor, a voltage equation, for each ECG electrode, by equating the ECG electrode voltage to a summation of a body voltage, the offset voltage, and a product of the current corresponding to the ECG electrode and the impedance, wherein values of the offset voltage, the body voltage, and the impedance are unknown; and

determining, by the at least one data processor, the impedance, for each ECG electrode, by solving the plurality of generated voltages equations to cancel out the offset voltage of the ECG electrode and the body voltage.

5. The method according to claim 1, wherein positive current flows from the ECG electrode to the patient body.

6. The method according to claim 1, wherein the adjusted plurality of currents is at least one of opposite polarity of the plurality of currents, double magnitude of the plurality of currents, and zero.

7. The method according to claim 1, wherein the current sources are Direct Current (DC) sources.

8. The method according to claim 1, wherein each of the plurality of current sources generate current of a magnitude less than or equal to two hundred nanoamperes.

9. The method according to claim 1, wherein the adjusted plurality of currents are maintained for a next calculation cycle.

10. The method according to claim 1, wherein the first reference ECG electrode or the second reference ECG electrode is either arbitrarily selected or selected to be an ECG electrode having a known impedance.

11. The method according to claim 1, further comprising providing the plurality of impedances for signal characterization of the monitored ECG electrodes.

12. A system comprising:

at least one data processor; and

memory storing instructions which, when executed by the at least one data processor, result in operations comprising;

monitoring electrocardiogram (ECG) electrodes each electrically connected to a patient body and a corresponding current source;

injecting one of a plurality of currents, each current having a respective predetermined level, into each ECG electrode;

measuring a plurality of ECG electrode voltages generated by the plurality of currents;

selecting a first reference ECG electrode from the monitored ECG electrodes, wherein unselected ECG electrodes include a plurality of non-reference ECG electrodes and a neutral drive electrode;

adjusting the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the respective predetermined level through the first reference ECG electrode; and

determining a plurality of impedances, each impedance corresponding to each non-reference ECG electrode, based on the plurality of ECG electrode voltages and the plurality of currents.

13. The system according to claim 12, wherein the operations further comprise:

selecting a second reference ECG electrode from the plurality of non-reference ECG electrodes;

adjusting the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the respective predetermined level through the second reference ECG electrode; and

determining impedances corresponding to the first reference ECG electrode and the neutral drive electrode based on the plurality of ECG electrode voltages and the plurality of currents.

14. The system according to claim 12, wherein the operations further comprise:

an electronic visual display for visually displaying vital signs of the patient body, wherein the non-transitory computer readable media and the electronic visual display form part of a patient monitor.

15. The system according to claim 12, further comprising the plurality of ECG electrodes.

16. The system according to claim 12, wherein each ECG electrode is modeled by an offset voltage and a resistor.

17. The system according to claim 16, wherein determining the plurality of impedances comprises:

generating a voltage equation, for each ECG electrode, by equating the ECG electrode voltage to a summation of a body voltage, an offset voltage of the ECG electrode, and a product of the current corresponding to the ECG electrode and the impedance, wherein values of the offset voltage of the ECG electrode, the body voltage, and the impedance are unknown; and

determining the impedance, corresponding to each non-reference ECG electrode, by solving the plurality of generated voltages equations to cancel out the offset voltage of the ECG electrode and the body voltage.

18. The system according to claim 12, wherein positive current flows from the electrode to the patient body.

19. The system according to claim 12, wherein the adjusted plurality of currents is at least one of opposite polarity of the plurality of currents, double magnitude of the plurality of currents, and zero.

20. The system according to claim 12, wherein the current sources are Direct Current (DC) sources.

21. The system according to claim 12, wherein each of the current sources generate current of a magnitude less than or equal to two hundred nanoamperes.

22. The system according to claim 12, wherein the adjusted plurality of current values are maintained for a next calculation cycle.

23. The system according to claim 12, wherein the first reference ECG electrode or the second reference ECG electrode is either arbitrarily selected or selected to be an ECG electrode having a known impedance.

24. The system according to claim 12, wherein the operations further comprise providing the plurality of impedances for signal characterization of the monitored ECG electrodes.

25. A computer programmable product comprising a computer-readable storage medium having computer-readable instructions stored in the computer-readable storage medium for executing the operations comprising:

monitoring electrocardiogram (ECG) electrodes each electrically connected to a patient body and a corresponding current source;

injecting one of a plurality of currents, each current having a respective predetermined level, into each ECG electrode;

measuring a plurality of ECG electrode voltages generated by the plurality of currents;

selecting a first reference ECG electrode from the monitored ECG electrodes, wherein unselected ECG electrodes include a plurality of non-reference ECG electrodes and a neutral drive electrode;

adjusting the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the predetermined level through the first reference ECG electrode; and

determining a plurality of impedances, each impedance corresponding to each non-reference ECG electrode of the ECG electrodes, based on the plurality of ECG electrode voltages and the plurality of currents.

26. The computer programmable product according to claim 25, wherein the operations further comprise:

selecting a second reference ECG electrode from the plurality of non-reference ECG electrodes;

adjusting the plurality of currents after measuring the plurality of ECG electrode voltages while maintaining the predetermined level through the second reference ECG electrode; and

determining impedances corresponding to the first reference ECG electrode and the neutral drive electrode based on the plurality of ECG electrode voltages and the plurality of currents.