Modified Sensor Calibration Algorithm

• US 20090112478A1
• Filed: 10/31/2007
• Published: 04/30/2009
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Wang, Lu, Mastrototaro, John J., Keenan, Desmond Barry, Mueller, John C. JR.
• Granted Patent: US 7,783,442 B2
• Time in Patent Office: Days
• US Class Current: 702/19
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• 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

A method of calibrating glucose monitor data includes collecting the glucose monitor data over a period of time at predetermined intervals, obtaining reference glucose values from a reference source that temporally correspond with the glucose monitor data obtained at the predetermined intervals, calculating the calibration characteristics using the reference glucose values and corresponding glucose monitor data to regress the obtained glucose monitor data, and calibrating the obtained glucose monitor data using the calibration characteristics. In additional embodiments, calculation of the calibration characteristics includes linear regression and, in particular embodiments, least squares linear regression. Alternatively, calculation of the calibration characteristics includes non-linear regression. Data integrity may be verified and the data may be filtered. Further, calibration techniques may be modified during a fast rate of change in the patient'"'"'s blood glucose level to increase sensor accuracy.

Claims

1. A method for calibrating a characteristic sensor comprising:

receiving a plurality of data values from the characteristic sensor;

obtaining a calibration reference value from another characteristic measuring device for the characteristic sensor;

comparing a parameter relating to at least one of the plurality of data values to a threshold value;

temporally correlating the calibration reference value with one of the plurality of data values using a first time delay if the parameter does not exceed the threshold value or with another one of the plurality of data values using a second time delay if the parameter is equal to or exceeds the threshold value;

calculating a calibration factor based on the calibration reference value and the data value temporally correlated with the calibration reference value; and

interpreting the plurality of data values using the calculated calibration factor.

2. The method of claim 1, wherein the characteristic sensor is a glucose sensor and the plurality of data values are blood glucose concentrations.

3. The method of claim 2, wherein the parameter is a rate of change in the blood glucose concentration, and the parameter comparison indicates a fast rate of change in the blood glucose concentration when the parameter is equal to or exceeds the threshold value.

4. The method of claim 3, wherein the second time delay is 5 minutes longer in duration than the first time delay.

5. The method of claim 4, wherein the first time delay is 15 minutes, and the second time delay is 20 minutes.

6. The method of claim 3, wherein the receiving a plurality of data values from the characteristic sensor further comprises:

sampling characteristic sensor data at a predetermined rate from the characteristic sensor over a period of time; and

deriving at least one of the plurality of data values from the sampled characteristic sensor data at a predetermined memory storage rate.

7. The method of claim 6, wherein the predetermined memory storage rate is once every 5 minutes.

8. The method of claim 6, wherein the predetermined memory storage rate is once every 1 minute.

9. The method of claim 3, wherein the receiving a plurality of data values from the characteristic sensor further comprises:

sampling characteristic sensor data at a predetermined rate from the characteristic sensor over a period of time;

deriving at least two intermediate data values from the sampled characteristic sensor data at a predetermined memory storage rate; and

deriving at least one of the plurality of data values at a rate faster than the predetermined memory storage rate by interpolation from the at least two intermediate data values.

10. The method of claim 9, wherein the predetermined memory storage rate is once every 5 minutes, and the at least one of the plurality of data values is derived at a rate of once every 1 minute by interpolation.

11. The method of claim 3, wherein the second time delay is selected from a plurality of predetermined time delays based on the rate of change in the blood glucose concentration, each of the plurality of predetermined time delays corresponding to a different predetermined rate of change in blood glucose concentration.

12. A method for calibrating sensor data collected from a characteristic sensor comprising:

obtaining a calibration reference value from another characteristic measuring device for the characteristic sensor;

calculating a current calibration factor based on the calibration reference value and a current sensor data point;

comparing a rate of change parameter relating to the current sensor data point to a threshold value;

reducing a weight of the current calibration factor if the rate of change parameter is equal to or exceeds the threshold value;

determining a calibration formula using the weighted current calibration factor; and

interpreting the collected sensor data using the calibration formula.

13. The method of claim 12, wherein the characteristic sensor is a glucose sensor and the collected sensor data are blood glucose concentrations.

14. The method of claim 13, wherein the rate of change parameter is a rate of change in the blood glucose concentration, and the parameter comparison indicates a fast rate of change in the blood glucose concentration when the parameter is equal to or exceeds the threshold value.

15. The method of claim 12, wherein the calibration formula is further based on past calibrations, the calibration formula weighting past calibrations based on how recent each past calibration factor was calculated and whether a rate of change parameter relating to each past sensor data point was equal to or exceeded the threshold value.

16. An apparatus for calibrating a characteristic sensor comprising:

means for receiving a plurality of data values from the characteristic sensor;

means for obtaining a calibration reference value from another characteristic measuring device for the characteristic sensor;

means for comparing a parameter relating to at least one of the plurality of data values to a threshold value;

means for temporally correlating the calibration reference value with one of the plurality of data values using a first time delay if the parameter does not exceed the threshold value or with another one of the plurality of data values using a second time delay if the parameter is equal to or exceeds the threshold value;

means for calculating a calibration factor based on the calibration reference value and the data value temporally correlated with the calibration reference value; and

means for interpreting the plurality of data values using the calculated calibration factor.

17. The apparatus of claim 16, wherein the characteristic sensor is a glucose sensor and the plurality of data values are blood glucose concentrations, and further wherein the parameter is a rate of change in the blood glucose concentration, and the parameter comparison indicates a fast rate of change in the blood glucose concentration when the parameter is equal to or exceeds the threshold value.

18. An apparatus for calibrating sensor data collected from a characteristic sensor comprising:

means for obtaining a calibration reference value from another characteristic measuring device for the characteristic sensor;

means for calculating a current calibration factor based on the calibration reference value and a current sensor data point;

means for comparing a rate of change parameter relating to the current sensor data point to a threshold value;

means for reducing a weight of the current calibration factor if the rate of change parameter is equal to or exceeds the threshold value;

means for determining a calibration formula using the weighted current calibration factor; and

means for interpreting the collected sensor data using the calibration formula.

19. The apparatus of claim 18, wherein the characteristic sensor is a glucose sensor and the collected sensor data are blood glucose concentrations, and further wherein the rate of change parameter is a rate of change in the blood glucose concentration, and the parameter comparison indicates a fast rate of change in the blood glucose concentration when the parameter is equal to or exceeds the threshold value.

20. The apparatus of claim 18, wherein the calibration formula is further based on past calibrations, the calibration formula weighting past calibrations based on how recent each past calibration factor was calculated and whether a rate of change parameter relating to each past sensor data point was equal to or exceeded the threshold value.