# US 10,368,805 B2 · Electrode impedance measurement

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- Number: US 10,368,805 B2
- Document ID: US10368805B2
- Status: Granted
- Kind: B2
- Application number: 15/394,349
- Filed: 2016-12-29
- Published: 2018-07-05
- Granted: 2019-08-06
- Earliest claimed: 2016-12-29
- Assignees: Drägerwerk AG & Co. KGaA
- Applicants: Draeger Medical Systems, Inc.
- Inventors: Derek Y. Qin
- Web page: https://patentgrep.com/patent/US10368805B2

## CPC

- A61B 5/6843: {Monitoring or controlling sensor contact pressure}
- A61B 5/0205: Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
- A61B 5/2415: {Measuring direct current [DC] or slowly varying biopotentials}
- A61B 5/308: for electrocardiography [ECG]
- A61B 5/053: Measuring electrical impedance or conductance of a portion of the body
- A61B 2562/0214: Capacitive electrodes
- A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D)

## 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

### Claim 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.

### Claim 2 (depends on 1)

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.

### Claim 3 (depends on 1)

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

### Claim 4 (depends on 3)

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.

### Claim 5 (depends on 1)

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

### Claim 6 (depends on 1)

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.

### Claim 7 (depends on 1)

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

### Claim 8 (depends on 1)

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.

### Claim 9 (depends on 1)

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

### Claim 10 (depends on 1)

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.

### Claim 11 (depends on 1)

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

### Claim 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.

### Claim 13 (depends on 12)

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.

### Claim 14 (depends on 12)

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.

### Claim 15 (depends on 12)

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

### Claim 16 (depends on 12)

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

### Claim 17 (depends on 16)

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.

### Claim 18 (depends on 12)

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

### Claim 19 (depends on 12)

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.

### Claim 20 (depends on 12)

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

### Claim 21 (depends on 12)

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.

### Claim 22 (depends on 12)

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

### Claim 23 (depends on 12)

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.

### Claim 24 (depends on 12)

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

### Claim 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.

### Claim 26 (depends on 25)

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.