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

• US 9,801,576 B2
• Filed: 03/01/2017
• Issued: 10/31/2017
• 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, Gautham, Raghavendhar, Liang, Bradley C., Shah, Rajiv
• Primary Examiner(s): Breene, John
• Assistant Examiner(s): MORGAN, JEFFREY CHAD
• Application Number:
  US15/446,886
• Publication Number:
  US 20170172474A1
• Time in Patent Office: 244 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 calculating a single, fused sensor glucose value based on respective glucose measurement signals of a plurality of redundant sensing electrodes, comprising:

performing respective electrochemical impedance spectroscopy (EIS) procedures for each of the plurality of redundant sensing electrodes to obtain values of at least one impedance-based parameter for each said sensing electrode;

measuring the electrode current (Isig) for each of the plurality of redundant sensing electrodes;

calculating a plurality of reliability indices for each said sensing electrode based on said values of the at least one impedance-based parameter, said plurality of reliability indices including a dip reliability index that is calculated by;

calculating a first similarity index to determine an amount of divergence between respective Isigs of at least a first one and a second one of said plurality of redundant sensing electrodes;

calculating a second similarity index to determine an amount of divergence between respective values of the at least one impedance-based parameter for said at least first one and second one of said plurality of redundant sensing electrodes;

mapping said first similarity index to said second similarity index; and

mapping said second similarity index to said first similarity index;

calculating a single fused Isig based on said plurality of reliability indices and respective Isig of each of the plurality of redundant sensing electrodes; and

calibrating said single fused Isig to obtain said single fused sensor glucose value.

2. The method of claim 1, wherein said impedance-based parameter is 1 kHz real impedance.

3. The method of claim 2, wherein said plurality of reliability indices include a bound check reliability index and a noise check reliability index.

4. The method of claim 3, wherein calculation of said bound check reliability index and noise check reliability index includes determining whether each said measured Isig and said values of the 1 kHz real impedance fall within respective predetermined ranges for a bound check and a noise check.

5. The method of claim 4, wherein said predetermined range for the 1 kHz real impedance bound check is between 0.3e+4 and 2e+4.

6. The method of claim 1, wherein said plurality of reliability indices include a sensitivity-loss index that is calculated based on each said electrode'"'"'s imaginary impedance.

7. The method of claim 6, wherein said imaginary impedance is measured at about 1 kHz over a period of time.

8. The method of claim 7, wherein said plurality of reliability indices include a bound check reliability index and a noise check reliability index, and wherein calculation of said bound check reliability index and said noise check reliability index include determining whether said values of the 1 kHz imaginary impedance fall within respective predetermined ranges for said bound check and noise check.

9. The method of claim 8, wherein said predetermined range for the 1 kHz imaginary impedance bound check is between −

2e+3 and zero.

10. The method of claim 1, wherein said plurality of reliability indices include a bound check reliability index and a noise check reliability index, and wherein said bound check reliability index and noise check reliability index are calculated based on values of 1 kHz imaginary impedance and 1 kHz real impedance.

11. The method of claim 10, wherein calculation of said bound check reliability index and noise check reliability index is further based on values of 0.105 Hz imaginary impedance and 0.105 Hz real impedance.

12. The method of claim 11, wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of the 0.105 Hz real impedance fall between 2e+4 and 7e+4.

13. The method of claim 11, wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of the 0.105 Hz imaginary impedance fall between −

2e+5 and 0.25e+5.

14. The method of claim 11, wherein calculation of said bound check reliability index and noise check reliability index is further based on values of Nyquist slope.

15. The method of claim 14, wherein calculation of said bound check reliability index and said noise check reliability index includes determining whether said values of Nyquist slope fall between 2 and 5.

16. The method of claim 1, wherein said single fused Isig is calibrated by using a blood glucose (BG) value.

17. The method of claim 1, wherein, prior to calculation of said single fused Isig, said respective measured Isig of each of the plurality of redundant sensing electrodes is first filtered to remove any EIS-induced spikes therein.

18. The method of claim 1, wherein one or more of the at least one impedance-based parameter are substantially glucose-independent.

19. The method of claim 1, further including calculating, for each of the plurality of electrodes, a weight based on said plurality of reliability indices for each said electrode.

20. The method of claim 19, wherein said single fused sensor glucose value is calculated based on the respective weights and Isigs of each of the plurality of redundant sensing electrodes.