Methods and systems for observing sensor parameters

• US 8,160,834 B2
• Filed: 06/02/2011
• Issued: 04/17/2012
• Est. Priority Date: 12/29/2008
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Liang, Bradley Chi, Tyler, Larry E., Askarinya, Mohsen, Gordon, Charles R., Schulhauser, Randal C., Cooper, Kenneth W., Holtzclaw, Kris R., Kannard, Brian T., Shah, Rajiv
• Primary Examiner(s): Nghiem, Michael
• Assistant Examiner(s): RIVERA VARGAS, MANUEL A
• Application Number:
  US13/151,601
• Publication Number:
  US 20110230741A1
• Time in Patent Office: 320 Days
• Field of Search: 702/65, 702/104, 702/116, 702/64, 702/182, 324/600, 324/609
• US Class Current: 702/104
• 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 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 (d) and the voltage measured in (f) that results from electrical resistance (R) in the sensor;

so that the state of the sensor is observed;

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

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

(j) observing a second voltage step between the voltage measured in (d) and/or (f) and/or (i) that results from electrical resistance (R) in the sensor;

(k) 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.

2. The method of claim 1, 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).

3. The method of claim 1, 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.

4. The method of claim 1, further comprising:

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

5. A method of observing a state of a sensor having a plurality of electrodes and a stable-state voltage (Vbase), the method comprising:

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

(b) forcing a current using the stable-state current (Ibase) measured in (a);

(c) changing the forced current to a second current comprising Ibase+deltaI, wherein deltaI comprises the difference between the Ibase and the second current;

(d) measuring an initially resulting voltage step (deltaV) due to resistance (R) in the sensor;

(e) changing the forced current to a third current comprising Ibase+deltaII, wherein deltaII comprises the difference between the Ibase and the third current;

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

(g) observing a second voltage step between the voltage measured in (d) and/or (f) that results from electrical resistance (R) in the sensor;

(h) calculating a voltage slope (dV/dt) using the voltage step measurement in (d), wherein the voltage slope so calculated is related to a charging of a sensor capacitance (C) by the deltaI applied to the sensor;

(i) calculating resistance (R) in the sensor using a formula R=deltaV/deltaI and calculating capacitance (C) in the sensor using a formula C=deltaI/(dV/dt);

so that the state of the sensor is observed.

6. The method of claim 5, 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.

7. The method of claim 5, further comprising:

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

8. The method of claim 5, wherein step (b) comprises keeping the sensor at the same voltage while forcing the current to the sensor.

9. The method of claim 5, wherein step (b) comprises allowing the sensor to stabilize at a slightly different voltage while forcing the current to the sensor.