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

• US 9,625,414 B2
• Filed: 11/05/2015
• Issued: 04/18/2017
• Est. Priority Date: 06/08/2012
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Yang, Ning, Shah, Rajiv
• Primary Examiner(s): Breene, John
• Assistant Examiner(s): Morgan, Jeffrey C
• Application Number:
  US14/933,372
• Publication Number:
  US 20160054424A1
• Time in Patent Office: 530 Days
• CPC Class Codes: A61B 2562/0214 Capacitive electrodes
• CPC Class Codes: A61B 2562/04 Arrangements of multiple sensors of the same type
• CPC Class Codes: A61B 5/0537 Measuring body composition by impedance, e.g. tissue hydration or fat content
• CPC Class Codes: A61B 5/0538 invasively, e.g. using a catheter
• CPC Class Codes: A61B 5/14503 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors A61B5/1459, A61B5/1464, A61B5/1473, A61B5/1482, A61B5/14865 take precedence
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/1459 invasive, e.g. introduced into the body by a catheter A61B5/1464 takes precedence
• CPC Class Codes: A61B 5/1473 invasive, e.g. introduced into the body by a catheter A61B5/1482 takes precedence
• CPC Class Codes: A61B 5/14865 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors
• CPC Class Codes: A61B 5/1495 Calibrating or testing of in-vivo probes
• CPC Class Codes: A61B 5/4839 combined with drug delivery
• CPC Class Codes: A61B 5/6849 in combination with a needle set
• CPC Class Codes: A61B 5/6852 Catheters
• CPC Class Codes: A61B 5/7203 for noise prevention, reduction or removal
• CPC Class Codes: A61B 5/7221 Determining signal validity, reliability or quality A61B5/7207 and A61B5/7217 take precedence
• CPC Class Codes: A61B 5/7225 Details of analog processing, e.g. isolation amplifier, gain or sensitivity adjustment, filtering, baseline or drift compensation A61B5/30, A61B5/316 take precedence; transformers for specific applications H01F38/00; amplifiers H03F
• CPC Class Codes: A61B 5/7242 using integration
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B
• CPC Class Codes: A61M 2005/1726 the body parameters being measured at, or proximate to, the infusion site
• CPC Class Codes: A61M 5/14244 adapted to be carried by the patient, e.g. portable on the body
• CPC Class Codes: A61M 5/14276 : specially adapted for implantation
• CPC Class Codes: A61M 5/1582 : Double lumen needles
• CPC Class Codes: A61M 5/1723 : using feedback of body parameters, e.g. blood-sugar, pressure measurement of body parameters A61B5/00
• CPC Class Codes: G01N 27/026 : Dielectric impedance spectroscopy electrochemical impedance spectroscopy for measuring corrosion G01N17/02
• CPC Class Codes: G01N 27/028 : Circuits therefor measuring impedance per se G01R27/02
• CPC Class Codes: G01N 27/416 : Systems G01N27/27 takes precedence
• CPC Class Codes: G01N 27/4163 : checking the operation of, or calibrating, the measuring apparatus G01N27/3274, G01N27/4175 and G01N33/0006 take precedence
• CPC Class Codes: G01N 33/49 : Blood chemical methods for determining blood cell populations G01N33/5094; chemical analysis of blood groups or blood types G01N33/80
• CPC Class Codes: G01N 33/66 : involving blood sugars, e.g. galactose
• CPC Class Codes: G01N 33/96 : involving blood or serum control standard
• CPC Class Codes: G01R 35/00 : Testing or calibrating of apparatus covered by the other groups of this subclass
• CPC Class Codes: G01R 35/005 : Calibrating; Standards or reference devices, e.g. voltage or resistance standards, "golden" references G01R33/0035, G01R35/002 take precedence

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.

Claims

1. A method of calibrating a sensor, comprising:

performing an electrochemical impedance spectroscopy (EIS) procedure for a working electrode of a sensor to obtain values of at least one impedance-based parameter for said working electrode;

performing a bound check on said values of the at least one impedance-based parameter to determine whether said at least one impedance-based parameter is in-bounds and, based on said bound check, calculating a reliability-index value for said working electrode; and

determining, based on the value of said reliability index, whether calibration should be performed, or whether calibration should be delayed until a later time.

2. The method of claim 1, wherein said at least one impedance-based parameter is substantially glucose-independent.

3. The method of claim 1, wherein said at least one impedance-based parameter includes real impedance.

4. The method of claim 3, wherein the real impedance is measured at 1 kHz.

5. The method of claim 4, wherein said at least one impedance-based parameter further includes Nyquist slope.

6. The method of claim 5, wherein calibration is performed if the value of said reliability index is above a low threshold value, and wherein calibration is delayed if the value of said reliability index is below a high threshold value.

7. The method of claim 6, wherein, if the value of said reliability index is below said high threshold value, then the trends of the 1 kHz real impedance and the Nyquist slope are monitored to estimate when respective values of the 1 kHz real impedance and the Nyquist slope will be in-bounds.

8. The method of claim 7, wherein, if it is estimated that respective values of the 1 kHz real impedance and the Nyquist slope will be in-bounds within a threshold amount of time, calibration is delayed until said respective values are in-bounds.

9. The method of claim 8, wherein, if it is estimated that it will take beyond a threshold amount of time for respective values of the 1 kHz real impedance and the Nyquist slope to be in-bounds, the sensor is calibrated without further delay.

10. The method of claim 1, wherein said sensor includes a plurality of redundant working electrodes.

11. The method of claim 10, wherein said EIS procedure is performed for each of said plurality of redundant working electrodes to obtain values of at least one impedance-based parameter for each said working electrode, wherein said bound check is performed on said values of the at least one impedance-based parameter for each said working electrode, and wherein a respective reliability index is calculated for each of the working electrodes.

12. The method of claim 11, wherein, for each of the working electrodes, each said respective reliability index is indicative of said electrode'"'"'s start-up characteristics.

13. The method of claim 12, further including, based on said respective reliability indices, selecting one of the plurality of redundant electrodes for obtaining glucose measurements.