Sensor systems, devices, and methods for continuous glucose monitoring

Abstract

Electrochemical impedance spectroscopy (EIS) may be used in conjunction with continuous glucose monitoring (CGM) to enable identification of valid and reliable sensor data, as well implementation of Smart Calibration algorithms.

1 . A method for real-time calibration of a glucose sensor for measuring the level of glucose in a body of a user, said sensor including physical sensor electronics, a microcontroller, and a working electrode, the method comprising:
 (a) measuring, by said physical sensor electronics, the electrode current (Isig) for the working electrode;   (b) obtaining a blood glucose (BG) value for said user;   (c) calculating, by said microcontroller, an expected calibration factor (CF) value based on said glucose sensor's age; and   (d) calculating, by said microcontroller, a calibrated sensor glucose (SG) value associated with said Isig based on said CF and BG values.   
     
     
         2 . The method of  claim 1 , wherein said expected calibration factor value is increased over time so as to reduce the likelihood of under-reading. 
     
     
         3 . The method of  claim 1 , wherein said expected calibration factor value is calculated according to the relation Expected CF=Sensor Age×(0.109 mg/dL/nA)/day+4.730 mg/dL/nA. 
     
     
         4 . The method of  claim 1 , further including storing said Isig value in a buffer. 
     
     
         5 . The method of  claim 1 , further including repeating steps (a)-(d) periodically. 
     
     
         6 . The method of  claim 1 , further including repeating step (a) at a calculated interval to obtain a plurality of Isig values prior to step (b). 
     
     
         7 . The method of  claim 6 , wherein step (c) is performed only when a BG value is obtained. 
     
     
         8 . The method of  claim 6 , wherein step (c) is performed for each of said plurality of Isig values. 
     
     
         9 . The method of  claim 1 , further including transmitting said calculated SG value to an insulin delivery device. 
     
     
         10 . The method of  claim 9 , wherein said insulin delivery device is an insulin pump. 
     
     
         11 . The method of  claim 10 , wherein said glucose sensor and said insulin pump cooperate in a closed-loop system. 
     
     
         12 . The method of  claim 1 , wherein said sensor includes a plurality of working electrodes, and steps (a)-(d) are performed for each of said plurality of electrodes. 
     
     
         13 . The method of  claim 1 , wherein said Isig value is filtered by said microcontroller to obtain a filtered Isig (fIsig) value. 
     
     
         14 . The method of  claim 1 , wherein said physical sensor electronics measure a plurality of Isig values at calculated intervals, and said microcontroller filters the plurality of Isig values to obtain respective filtered Isig (fIsig) values. 
     
     
         15 . The method of  claim 14 , further including storing at least a subset of said fIsig values in a calibration buffer. 
     
     
         16 . The method of  claim 15 , further including assigning respective weights to said subset of fIsig values stored in the calibration buffer. 
     
     
         17 . The method of  claim 16 , further including performing an electrochemical impedance spectroscopy (EIS) procedure for said working electrode to obtain a respective plurality of values of an impedance-based parameter for said electrode, and modifying said respective weights based on said values of the impedance-based parameter. 
     
     
         18 . Then method of  claim 17 , wherein said expected calibration factor value is calculated according to the relation Expected CF=Sensor Age×(0.109 mg/dL/nA)/day+4.730 mg/dL/nA. 
     
     
         19 . Then method of  claim 18 , further including transmitting said calculated SG value to an insulin delivery device. 
     
     
         20 . The method of  claim 16 , further including performing an electrochemical impedance spectroscopy (EIS) procedure for said working electrode to obtain a respective plurality of values of an impedance-based parameter for said electrode, and clearing the calibration buffer if said values of the impedance-based parameter are outside of a calculated range.