Methods, systems, and devices for calibration and optimization of glucose sensors and sensor output
A continuous glucose monitoring system may utilize externally sourced information regarding the physiological state and ambient environment of its user for externally calibrating sensor glucose measurements. Externally sourced factory calibration information may be utilized, where the information is generated by comparing metrics obtained from the data used to generate the sensor's glucose sensing algorithm to similar data obtained from each batch of sensors to be used with the algorithm in the future. The output sensor glucose value of a glucose sensor may also be estimated by analytically optimizing input sensor signals to accurately correct for changes in sensitivity, run-in time, glucose current dips, and other variable sensor wear effects. Correction actors, fusion algorithms, EIS, and advanced ASICs may be used to implement the foregoing, thereby achieving the goal of improved accuracy and reliability without the need for blood-glucose calibration, and providing a calibration-free, or near calibration-free, sensor.
1. A method for measuring a level of glucose in a body of a user using a glucose sensor, the glucose sensor comprising physical sensor electronics, a microcontroller, and a working electrode, the method comprising:
periodically measuring, by the physical sensor electronics, electrode current (Isig) signals for the working electrode;
performing, by the microcontroller, an Electrochemical Impedance Spectroscopy (EIS) procedure to generate EIS-related data for the working electrode;
calculating, by the microcontroller, an adjusted calibration factor for the glucose sensor based on the EIS-related data;
calculating, by the microcontroller, an adjusted offset value for the glucose sensor based on at least one of an adjustment of a stabilization time of the glucose sensor or an adjustment of a non-linear response of the glucose sensor; and
providing, by the microcontroller, a measured glucose value (SG) based on the adjusted calibration factor and the adjusted offset value,
wherein SG=(adjusted calibration factor)×(Isig+adjusted offset value), and
wherein the adjusted calibration factor is calculated based on a stabilization response for the glucose sensor.
2. The method of claim 1 , further including displaying the measured glucose value to the user.
3. The method of claim 1 , wherein the glucose sensor further comprises a counter electrode and the adjusted calibration factor is further calculated based on an oxygen response, wherein the oxygen response is calculated as:
oxygen
response
=
c
1
×
Vcntr
2
+
c
2
×
Vcntr
+
c
3
,
wherein Ventr is a counter voltage input and c 1 , c 2 , and c 3 are experimentally determined calibration coefficients.
4. The method of claim 1 , wherein the adjusted calibration factor is further calculated based on a dip adjustment response, wherein the dip adjustment response is calculated as:
dip
adjustment
response
=
c
1
×
e
IsigTrend
×
c
2
+
c
3
,
wherein IsigTrend is a long-term sensor current trend input and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.
5. The method of claim 1 , wherein the glucose sensor further comprises a counter electrode and the stabilization response is calculated as:
stabilization
response
=
c
1
×
Vcntr
+
c
2
,
where Vcntr is a counter voltage input and c 1 and c 2 are experimentally determined calibration coefficients.
6. The method of claim 3 , wherein the adjusted calibration factor is calculated based on a foreign body response of the glucose sensor, the oxygen response, and the stabilization response for the glucose sensor.
7. The method of claim 1 , wherein the adjustment of the stabilization time for calculation of the adjusted offset value is calculated as:
adjustment of the
stabilization
time
=
c
1
×
e
age
×
c
2
+
c
3
,
wherein age is a sensor age, and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.
8. The method of claim 7 , wherein the sensor age is measured from one of sensor warm-up completion, sensor insertion, or sensor calibration completion.
9. The method of claim 1 , wherein the adjustment of the non-linear response for calculation of the adjusted offset value is calculated as:
adjustment of the non-linear response=c 1 +(age×c 2 +c 3 )×Isig,
wherein age is the sensor age, and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.
10. An apparatus comprising:
a glucose sensor for measuring a level of glucose in a body of a user, the glucose sensor comprising:
physical sensor electronics;
a working electrode; and
a microcontroller configured to execute instructions to at least perform:
periodically measuring, by the physical sensor electronics, electrode current (Isig) signals for the working electrode;
performing, by the microcontroller, an Electrochemical Impedance Spectroscopy (EIS) procedure to generate EIS-related data for the working electrode;
calculating, by the microcontroller, an adjusted calibration factor for the glucose sensor based on the EIS-related data;
calculating, by the microcontroller, an adjusted offset value for the glucose sensor based on at least one of an adjustment of a stabilization time of the glucose sensor or an adjustment of a non-linear response of the glucose sensor; and
providing, by the microcontroller, a measured glucose value (SG) based on the adjusted calibration factor and the adjusted offset value,
wherein SG=(adjusted calibration factor)×(Isig+adjusted offset value), and
wherein the adjusted calibration factor is calculated based on a stabilization response for the glucose sensor.
11. The apparatus of claim 10 , further comprising a display screen configured to display the measured glucose value to the user.
12. The apparatus of claim 10 , wherein the glucose sensor further comprises a counter electrode and the adjusted calibration factor is further calculated based on an oxygen response, wherein the oxygen response is calculated as:
oxygen
response
=
c
1
×
Vcntr
2
+
c
2
×
Vcntr
+
c
3
,
wherein Ventr is a counter voltage input and c 1 , c 2 , and c 3 are experimentally determined calibration coefficients.
13. The apparatus of claim 10 , wherein the adjusted calibration factor is further calculated based on a dip adjustment response, wherein the dip adjustment response is calculated as:
dip
adjustment
response
=
c
1
×
e
IsigTrend
×
c
2
+
c
3
,
wherein IsigTrend is a long-term sensor current trend input and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.
14. The apparatus of claim 10 , wherein the glucose sensor further comprises a counter electrode and the stabilization response is calculated as:
stabilization
response
=
c
1
×
Vcntr
+
c
2
,
where Ventr is the counter voltage input and c 1 and c 2 are experimentally determined calibration coefficients.
15. The apparatus of claim 13 , wherein the adjusted calibration factor is calculated based on a foreign body response of the glucose sensor, the dip adjustment response, and the stabilization response for the glucose sensor.
16. The apparatus of claim 10 , wherein the adjustment of the stabilization time for calculation of the adjusted offset value is calculated as:
adjustment of the
stabilization
time
=
c
1
×
e
age
×
c
2
+
c
3
,
wherein age is a sensor age, and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.
17. The apparatus of claim 16 , wherein the sensor age is measured from one of sensor warm-up completion, sensor insertion, or sensor calibration completion.
18. The apparatus of claim 10 , where the adjustment of the non-linear response for calculation of the adjusted offset value is calculated as:
adjustment to the
non
-
linear
response
=
c
1
+
(
age
×
c
2
+
c
3
)
×
Isig
,
wherein age is the sensor age, and c 1 , c 2 and c 3 are experimentally determined calibration coefficients.