METHODS AND SYSTEMS FOR OBSERVING SENSOR PARAMETERS

• US 20100169035A1
• Filed: 12/29/2008
• Published: 07/01/2010
• Est. Priority Date: 12/29/2008
• Status: Abandoned Application

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Shah, Rajiv, Gordon, Charles Robert, Schulhauser, Randal C., Cooper, Kenneth W., Kannard, Brian T., Liang, Bradley Chi, Holtzclaw, Kris R., Tyler, Larry E., Askarinya, Mohsen
• Application Number:
  US12/345,354
• Publication Number:
  US 20100169035A1
• Time in Patent Office: Days
• US Class Current: 702/65
• CPC Class Codes: A61B 5/14532 for measuring glucose, e.g. by tissue impedance measurement
• CPC Class Codes: A61B 5/14865 invasive, e.g. introduced into the body by a catheter or needle or using implanted sensors

Abstract

The invention disclosed herein provides methods and materials for observing the state of a sensor, for example those used by diabetic patients to monitor blood glucose levels. Typically a voltage such as a voltage pulse is applied to the sensor in order to solicit a current response from which for example, factors such as impedance values can be derived. Such values can then be used as indicators of a sensor'"'"'s state, for example the state of sensor hydration, sensor noise, sensor offset, sensor drift or the like.

Claims

1. A method of observing a state of a sensor having a plurality of electrodes, the method comprising:

(a) applying voltage to the sensor;

(b) observing a peak instantaneous electrical current of the sensor; and

(c) observing a total current of the sensor over a period of time for a predetermined frequency;

so that the state of the sensor is observed.

2. The method of claim 1, wherein observations of the peak instantaneous electrical current and/or the total current in the sensor over a period of time for a predetermined frequency are used to estimate sensor impedance magnitude.

3. The method of claim 1, wherein observations of the peak instantaneous electrical current and/or the total current in the sensor over a period of time for a predetermined frequency are used to estimate sensor capacitance.

4. The method of claim 1, wherein observations on the state of the sensor provide information on:

sensor hydration;

sensor noise;

sensor offset;

or

sensor drift.

5. The method of claim 3, wherein an estimate of sensor capacitance comprises a voltage step analysis using a formula:

6. The method of claim 1, wherein step (a) comprises applying a voltage pulse to the sensor.

7. The method of claim 6, wherein the method comprises:

observing the maximum current value (counts/second) during the initial 2 seconds in response to a voltage pulse applied to the sensor, and

comparing the maximum current value to a predetermined test value.

8. The method of claim 1, wherein step (a) comprises applying a plurality of voltages to the sensor.

9. The method of claim 1, wherein step (c) comprises observing current in the sensor over multiple periods of time.

10. The method of claim 1, wherein step (c) comprises observing current in the sensor over multiple frequencies.

11. The method of claim 1, further comprising:

performing the method on a plurality of sensors; and

comparing the information so obtained on the state of the plurality of sensors.

12. The method of claim 1, wherein the sensor is a glucose sensor.

13. The method of claim 12, wherein the glucose sensor comprises:

a base layer;

at least three working electrodes disposed on the base layer;

a glucose oxidase layer disposed upon the working electrodes;

an analyte modulating layer disposed on the glucose oxidase layer, wherein the analyte modulating layer comprises a hydrogel composition; and

an adhesion promoting layer disposed between the glucose oxidase layer and the analyte modulating layer.

14. A sensor system, comprising:

an implantable sensor, the sensor including a plurality of electrodes;

a sensor electronics device, the sensor electronics device capable of being operably connected to the sensor, and the sensor electronics device including;

a connection detection device to determine if the sensor electronics device is connected to the sensor and to transmit a connection signal;

a power source to supply a regulated voltage;

a microprocessor; and

a computer-readable program code having instructions, which when executed cause the microprocessor to;

(a) apply a voltage to the sensor;

(b) record data on a peak instantaneous electrical current of the sensor in response to the applied voltage; and

(c) record data on a total current of the sensor over a period of time for a predetermined frequency in response to the applied voltage.

15. The system of claim 14, further comprising a monitor for displaying the recorded data from steps (b) and/or (c), wherein the data displayed on the monitor provides information on:

sensor hydration;

sensor noise;

sensor offset;

or

sensor drift.

16. The system of claim 15, wherein recorded data from steps (b) and/or (c) are used to estimate sensor capacitance using a formula:

17. The system of claim 14, wherein:

step (a) comprises applying a plurality of voltages to the sensor;

or

step (a) comprises;

applying a voltage pulse to the sensor; and

step (c) comprises recording data on a current in the sensor over multiple periods of time;

or

step (c) comprises recording data on a current in the sensor over multiple frequencies.

18. The system of claim 14, wherein the implantable sensor is a glucose sensor comprising:

a base layer;

at least three working electrodes disposed on the base layer;

a glucose oxidase layer disposed upon the working electrodes;

an analyte modulating layer disposed on the glucose oxidase layer; and

an adhesion promoting layer disposed between the glucose oxidase layer and the analyte modulating layer.

19. The system of claim 14, wherein the sensor is implantable in tissue selected from the group consisting of subcutaneous, dermal, sub-dermal, intra-peritoneal, and peritoneal tissue.

20. A program code storage device, comprising:

a computer-readable medium;

a computer-readable program code, stored on the computer-readable medium, the computer-readable program code having instructions, which when executed cause a controller to;

initiate a series of voltage pulses to be applied to a sensor comprising a plurality of electrodes; and

receive a signal from a detection circuit, the signal indicating;

(a) a peak instantaneous electrical current of the sensor in response to the applied voltage pulses; and

(b) a total current of the sensor over a period of time for a predetermined frequency in response to the applied voltage pulses.

21. The program codes storage device of claim 20, including instructions, which when executed causes the controller to:

determine the maximum current value (counts/second) during the initial 2 seconds in response to a voltage pulse applied to the sensor, and

compare the maximum current value so determined to a predetermined range of values; and

utilize a sensor signal received from the sensor to measure a physiological characteristic of a patient when the value is within the predetermined range of values.

22. The program codes storage device of claim 20, including instructions, which when executed cause a controller to initiate a sensor observation routine;

and

transmit a first signal to a digital-to-analog converter (DAC), the DAC being coupled to an electrode of a sensor, the first signal representative of a observation sequence of voltages that the DAC is to output to the electrode of the sensor, wherein the observation sequence of voltages includes;

a first voltage applied for a first time frame;

a second voltage applied for a second time frame;

and a repeating of the application of the first voltage and the second voltage to the electrodes.

23. The program code storage device of claim 22, including instructions, which when executed cause the controller to:

repeat the application of the first voltage and the second voltage for a number of iterations.

24. The program code storage device of claim 23, including instructions, which when executed cause the controller to:

change a duration of the first amount of time and a duration of the second amount of time for at least one of the number of iterations.

25. The program code storage device of claim 22, including instructions, which when executed cause the controller to:

instruct the DAC to change a magnitude of the first voltage to be applied to the electrode of the sensor at least once during the repeating of the application of the first voltage;

or

instruct the DAC to change a magnitude of the second voltage to be applied to the electrode of the sensor at least once during the repeating of the application of the second voltage.

26. A method of observing a state of a sensor having a plurality of electrodes, the method comprising:

(a) applying a voltage to the sensor;

(b) measuring a stable-state current (Ibase) produced in response to the voltage applied to the sensor;

(c) applying the stable-state current measured in (b) to the sensor;

(d) measuring sensor voltage during the application of the stable-state current;

(e) changing applied sensor current to a second current comprising Ibase+deltaI, wherein deltaI comprises the difference between the Ibase and the second current;

(f) measuring sensor voltage during the application of the second current;

(g) observing a first voltage step between the voltage measured in (b) and the voltage measured in (f) that results from electrical resistance (R) in the sensor;

so that the state of the sensor is observed.

27. The method of claim 26, further comprising:

(i) changing applied sensor current to a third current comprising Ibase+deltaII, wherein deltaII comprises the difference between the Ibase and the third current;

(ii) measuring sensor voltage during the application of the third current;

(iii) observing a second voltage step between the voltage measured in (b) and/or (F and/or (ii) that results from electrical resistance (R) in the sensor; and

(iv) calculating a voltage slope (dV/dt) using multiple voltage step measurements, wherein the voltage slope so calculated is correlated to a change in sensor capacitance (C) that results from the different currents applied to the sensor.

28. The method of claim 27, wherein:

calculating resistance (R) in the sensor using a formula R=deltaV/deltaI; and

/or

calculating capacitance (C) in the sensor using a formula C=deltaI/(dV/dt).

29. The method of claim 26, wherein the sensor is an electrochemical glucose sensor implanted in vivo and the observation of the state of the sensor provides information on:

sensor hydration;

sensor noise;

sensor offset;

or

sensor drift.

30. The method of claim 26, further comprising:

performing the method on a plurality of sensors made by differing manufacturing processes; and

comparing the information so obtained on the state of the plurality of sensors.