System and methods for calibrating physiological characteristic sensors

• US 7,783,442 B2
• Filed: 10/31/2007
• Issued: 08/24/2010
• Est. Priority Date: 10/31/2007
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Mueller, John C. Jr., Wang, Lu, Mastrototaro, John J., Keenan, Desmond Barry
• Primary Examiner(s): Wachsman; Hal D
• Application Number:
  US11/931,866
• Publication Number:
  US 20090112478A1
• Time in Patent Office: 1,028 Days
• Field of Search: 702/85, 702/23, 702/32, 702/104
• US Class Current: 702/85
• 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.

Claims

1. A method for calibrating a characteristic sensor using a characteristic sensor monitor, comprising:

receiving a plurality of data values from the characteristic sensor;

obtaining a calibration reference value from a separate characteristic measuring device;

calculating a parameter of at least one of the plurality of data values;

comparing the parameter to a threshold parameter value;

calculating a temporally correlated data value, wherein the temporally correlated data value is calculated by;

temporally correlating the calibration reference value with one of the plurality of data values using a first time delay, wherein the first time delay is used if the parameter is less than the threshold parameter value;

or

temporally correlating the calibration reference value with another one of the plurality of data values using a second time delay, wherein the second time delay is used if the parameter is equal to or exceeds the threshold parameter value;

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

interpreting the plurality of data values using the calibration factor; and

storing the calibration factor on the characteristic sensor monitor,

wherein the characteristic sensor is a glucose sensor and the plurality of data values are blood glucose concentrations,

wherein the parameter is a rate of change in the blood glucose concentration, and wherein a fast rate of change in the blood glucose concentration exists when the parameter is equal to or exceeds the threshold parameter value, and

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.

2. The method of claim 1, 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.

3. A method for calibrating sensor data collected from a characteristic sensor using a characteristic sensor monitor, comprising:

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

obtaining a calibration reference value from a separate characteristic measuring device;

calculating a current calibration factor based on the calibration reference value and a current sensor data value obtained from the plurality of sensor data values;

calculating a parameter of the current sensor data value, wherein the parameter is a rate of change;

comparing the parameter to a threshold parameter value;

calculating a weighted current calibration factor by reducing a weight of the current calibration factor if the parameter is equal to or exceeds the threshold parameter value;

applying the weighted current calibration factor to a calibration formula; and

interpreting the plurality of sensor data values using the calibration formula,

wherein the calibration formula is based on at least one past calibration, the calibration formula weighting the at least one past calibration based on how recent at least one past calibration factor was calculated and whether a past parameter of a past sensor data value was equal to or exceeded the threshold parameter value, wherein the past parameter is a past rate of change.

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

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

means for obtaining a calibration reference value from a separate characteristic measuring device;

means for calculating a current calibration factor based on the calibration reference value and a current sensor data value obtained from the plurality of sensor data values;

means for calculating a parameter of the current sensor data value, wherein the parameter is a rate of change;

means for comparing the parameter to a threshold parameter value;

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

means for applying the weighted current calibration factor to a calibration formula; and

means for interpreting the plurality of sensor data values using the calibration formula,

wherein the calibration formula is based on at least one past calibration, the calibration formula weighting the at least one past calibration based on how recent at least one past calibration factor was calculated and whether a past parameter of a past sensor data value was equal to or exceeded the threshold parameter value, wherein the past parameter is a past rate of change.