Methods, systems, and devices for continuous glucose monitoring
A continuous glucose monitoring system may utilize electrode current (Isig) signals, Electrochemical Impedance Spectroscopy (EIS), and Vcntr values to optimize sensor glucose (SG) calculation in such a way as to enable reduction of the need for blood glucose (BG) calibration requests from users.
1. A method of optimizing a sensor glucose (SG) calculation for a glucose sensor used for measuring the level of glucose in the body of a user, said glucose sensor including physical sensor electronics, a microcontroller, a counter electrode, and a working electrode, the method comprising:
(a) periodically measuring, by the physical sensor electronics, electrode current (Isig) signals for the working electrode;
(b) periodically performing, by the microcontroller, an Electrochemical Impedance Spectroscopy (EIS) procedure by causing an alternating current (AC) source to apply a periodic AC signal to the working electrode to generate EIS-related data for the working electrode;
(c) periodically measuring, by the physical sensor electronics, a potential difference between the counter electrode and the working electrode (Vcntr);
(d) periodically obtaining a blood glucose (BG) value for the user;
(e) determining in real-time, by said microcontroller, whether a calibration error exists;
(f) when there is no calibration error, calculating in real-time, by said microcontroller, a sensor glucose (SG) value based on said BG, Isig, Vcntr, and EIS-related data; and
(g) causing the microcontroller to communicate the calculated SG value to at least one of an insulin-administering device or a mobile communication device.
2. The method of claim 1 , further including displaying the SG value to the user.
3. The method of claim 1 , further including storing calibration information in a calibration buffer, wherein said calibration information includes up to 15 sets of calibration data, each said data set including a timestamp of the BG value.
4. The method of claim 3 , further including calculating a calibration ratio (CR) based on the information stored in the calibration buffer.
5. The method of claim 4 , wherein the calculated CR is weighted based on the most-recent calibration time and the time of each said BG in the calibration buffer.
6. The method of claim 1 , further including, prior to step (g), repeating steps (d)-(e) if it is determined that a calibration error exists, and terminating the glucose sensor when two consecutive calibration errors have occurred.
7. The method of claim 1 , further including calculating a noise signal level based on said Isig signals, and terminating the glucose sensor when the noise signal level exceeds a threshold for the duration of a predetermined time window.
8. The method of claim 7 , wherein said predetermined time window comprises three consecutive periods of time, each said period of time having a duration of two hours.
9. The method of claim 8 , wherein said noise signal level calculation starts when the glucose sensor has an age of at least 24 hours.
10. The method of claim 7 , wherein said glucose sensor is terminated without calibration.
11. The method of claim 1 , further including monitoring the value of 1 kHz real impedance, and terminating the glucose sensor when the value of 1 kHz real impedance exceeds a threshold.
12. The method of claim 11 , wherein the glucose sensor is terminated when 1 kHz real impedance exceeds 12,000 Ohms.
13. The method of claim 11 , wherein the glucose sensor is terminated when 1 kHz real impedance exceeds 10,500 Ohms for two hours or more.
14. The method of claim 1 , further including calculating, by said microcontroller, a rate of change of SG over a period of time.
15. The method of claim 1 , further including calculating, by said microcontroller, a rate of change of Isig over a period of time.