Application of electrochemical impedance spectroscopy in sensor systems, devices, and related methods

Patent metadata

Field	Value
Publication number	US-9863911-B2
Application number	US-201715666887-A
Country	US
Kind code	B2
Filing date	Aug 2, 2017
Priority date	Jun 8, 2012
Publication date	Jan 9, 2018
Grant date	Jan 9, 2018

Abstract

A diagnostic Electrochemical Impedance Spectroscopy (EIS) procedure is applied to measure values of impedance-related parameters for one or more sensing electrodes. The parameters may include real impedance, imaginary impedance, impedance magnitude, and/or phase angle. The measured values of the impedance-related parameters are then used in performing sensor diagnostics, calculating a highly-reliable fused sensor glucose value based on signals from a plurality of redundant sensing electrodes, calibrating sensors, detecting interferents within close proximity of one or more sensing electrodes, and testing surface area characteristics of electroplated electrodes. Advantageously, impedance-related parameters can be defined that are substantially glucose-independent over specific ranges of frequencies. An Application Specific Integrated Circuit (ASIC) enables implementation of the EIS-based diagnostics, fusion algorithms, and other processes based on measurement of EIS-based parameters.

First claim

What is claimed is:

1. A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor of a sensor system, said sensor including at least one working electrode and said sensor system including a microprocessor that is operatively connected to said sensor, the method comprising:
(a) periodically performing an electrochemical impedance spectroscopy (EIS) procedure to generate multiple sets of impedance-related data for said at least one working electrode;
(b) calculating, by said microprocessor, respective values of a plurality of impedance-related parameters based on said multiple sets of impedance-related data, said plurality of parameters including impedance, phase angle, and Nyquist slope; and
(c) based on said respective values, determining, by said microprocessor, whether the sensor is functioning normally, wherein the microprocessor:
(i) performs a first test based on values of real impedance or phase angle;
(ii) performs a second test based on values of respective frequencies at which successive EIS procedures are performed;
(iii) performs a third test based on a comparison of current and post-sensor initialization impedance values at 1 kHz;
(iv) performs a fourth test based on the value of post-sensor initialization impedance at 0.1 Hz;
(v) performs a fifth test based on a global change in the value of Nyquist slope between 0.1 Hz and 1 Hz;
(vi) performs a sixth test based on a change, over time, in the magnitude of real impedance;
(vii) determines that the sensor is functioning normally if at least 3 of said first through sixth tests are satisfied by generating results that fall within respective predetermined criteria,
wherein the microprocessor determines that the first test is satisfied if either |(Zn−ZI)/ZI|>30% at 1 kHz, wherein Z1 is the value of real impedance measured at a first EIS run and Zn is the value of real impedance measured at a subsequent EIS run, or the phase angle change is greater than 10° at 0.1 Hz between said first and subsequent EIS runs,
wherein the microprocessor determines that the second test is satisfied if, at a phase angle of −45°, the difference in frequency between two consecutive EIS runs (f2-fl) is greater than 10 Hz, and
wherein the microprocessor determines that the third test is satisfied if the current value of impedance is less than the post-initialization value of impedance at 1 kHz.

2. The method of claim 1 , wherein the microprocessor determines that the fourth test is satisfied if the value of impedance is less than 300 kOhms at 0.1 Hz during post-initialization sensor operation.

3. The method of claim 1 , wherein the microprocessor determines that the fifth test is satisfied if the value of Nyquist slope is determined to be globally increasing from 0.1 Hz to 1 Hz.

4. The method of claim 1 , wherein the microprocessor determines that the sixth test is satisfied if the value of real impedance is determined to be globally decreasing over successive EIS runs.

5. The method of claim 1 , wherein, after step (b) but before step (c)(i), the microprocessor determines whether said sensor is properly inserted or implanted.

6. The method of claim 5 , wherein the microprocessor determines that the sensor is not properly inserted or implanted if the slope of the absolute value of impedance is determined to be constant across a predetermined range of frequencies, or the phase angle is about −90°, or both.

7. The method of claim 1 , wherein each of the first through sixth tests is weighted.

8. The method of claim 7 , wherein the respective weight for at least one of the first through sixth tests is different than the weight for at least one other of the first through sixth tests.

9. A method of performing real-time sensor diagnostics on a subcutaneous or implanted sensor of a sensor system, said sensor including at least one working electrode and said sensor system including a microprocessor that is operatively connected to said sensor, the method comprising:
(a) periodically performing an electrochemical impedance spectroscopy (EIS) procedure to generate multiple sets of impedance-related data for said at least one working electrode;
(b) calculating, by said microprocessor, respective values of a plurality of impedance-related parameters based on said multiple sets of impedance-related data, said plurality of parameters including impedance, phase angle, and Nyquist slope; and
(c) based on said respective values, determining, by said microprocessor, whether the sensor is functioning normally, wherein the microprocessor:
(i) performs a first test based on values of real impedance or phase angle;
(ii) performs a second test based on values of sensor current (Isig) and impedance magnitude at 1 kHz;
(iii) performs a third test based on a global change in the value of Nyquist slope between 0.1 Hz and 1 Hz;
(iv) performs a fourth test based on the values of phase angle and impedance magnitude at 0.1 Hz;
(v) performs a fifth test based on values of impedance magnitude and Isig;
(vi) performs a sixth test based on values of Isig, phase angle, and imaginary impedance;
(vii) performs a seventh test based on values of Isig and imaginary impedance at 0.1 Hz;
(viii) determines that the sensor is functioning normally if at least 4 of said first through seventh tests are satisfied by generating results that fall within respective predetermined criteria,
wherein the microprocessor determines that the first test is satisfied if either |(Zn−ZI)/ZI|>30% at 1 kHz, wherein Z1 is the value of real impedance measured at a first EIS run and Zn is the value of real impedance measured at a second EIS run that occurs 2 hours after the first EIS run, or the phase angle change is greater than 10° at 0.1 Hz between said first and second EIS runs,
wherein the microprocessor determines that the second test is satisfied if the percentage change in the value of impedance magnitude at 1 kHz is less than or equal to 30%, or if the percentage change in the Isig is less than or equal to 30% between a first EIS run and a second EIS run performed 2 hours after said first EIS run,
wherein the microprocessor determines that the third test is satisfied if the value of Nyquist slope is determined to be globally increasing from 0.1 Hz to 1 Hz, and
wherein the microprocessor determines that the fourth test is satisfied if the value of the phase angle at 0.1 Hz is determined not to be continuously increasing over time, and the value of impedance magnitude at 0.1 Hz is determined not to be continuously increasing over time.

10. The method of claim 9 , wherein the microprocessor determines that the fifth test is satisfied if the percentage change in the value of impedance magnitude at 1 kHz is less than or equal to 30%, or if the percentage change in the Isig is less than or equal to 30% between a first EIS run and a second EIS run.

11. The method of claim 9 , wherein the microprocessor determines that the sixth test is satisfied if at least two out of the following three criteria are met: (a) Isig is greater than or equal to 10 nA; (b) the value of imaginary impedance at 1 kHz is greater than or equal to −1500 Ohm; and (c) the phase angle at 1 kHz is greater than or equal to −15°.

12. The method of claim 9 , wherein the microprocessor determines that the seventh test is satisfied if, at 0.1 Hz, the magnitude of the difference between the value of a first ratio of the imaginary impedance to the Isig from a first EIS run and the value of a second ratio of the imaginary impedance to the Isig from a second EIS run is less than or equal to 30% of the value of said ratio from the first EIS run.

13. The method of claim 9 ,

Assignees

• Medtronic Minimed Inc

Inventors

• Wang Jenn-Hann Larry
• Miller Michael E
• Gautham Raghavendhar
• Li Yiwen
• Shah Rajiv

Classifications

• A61B5/7221 Primary

  Determining signal validity, reliability or quality (preventing, reducing or removing noise induced by motion artefacts A61B5/7207; noise originating from a therapeutic or surgical apparatus A61B5/7217) · CPC title

• A61B5/746

  Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms · CPC title

• A61B5/0537

  Measuring body composition by impedance, e.g. tissue hydration or fat content · CPC title

• A61M5/1582

  Double lumen needles · CPC title

• A61B5/14865

  invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors · CPC title