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 determining the validity of glucose sensor data, said glucose sensor including physical sensor electronics, a microcontroller, and a working electrode, and being in operational contact with a display device configured to display said data to a user, the method comprising:
 (a) performing, by said microcontroller, an electrochemical impedance spectroscopy (EIS) procedure to obtain real impedance values for said electrode;   (b) filtering, by said microcontroller, said real impedance values;   (c) analyzing said real impedance values by said microcontroller to determine whether said values are stable;   (d) if said real impedance values are stable, comparing the most-recent real impedance value to a first threshold value; and   (e) based on said comparison, determining whether said sensor data is valid.   
     
     
         2 . The method of  claim 1 , wherein said real impedance values are 1 kHz real impedance values. 
     
     
         3 . The method of  claim 1 , wherein, if the glucose sensor data is determined to be valid, said data is transmitted to be displayed on said display device. 
     
     
         4 . The method of  claim 1 , wherein said first threshold value is 10,000Ω. 
     
     
         5 . The method of  claim 4 , wherein the sensor data is determined to be valid if the most-recent real impedance value is less than the first threshold value. 
     
     
         6 . The method of  claim 5 , wherein, if the most-recent real impedance value is greater than the first threshold value, the method further includes determining, by the microcontroller, whether said real impedance values have exceeded a second threshold over a period of time. 
     
     
         7 . The method of  claim 6 , wherein said period of time is the past 3 hours. 
     
     
         8 . The method of  claim 7 , wherein if it is determined that the real impedance values have exceeded said second threshold over the past 3 hours, then said sensor is terminated. 
     
     
         9 . The method of  claim 7 , wherein, if it is determined that the real impedance values have not exceeded said second threshold over the past 3 hours, then said sensor data is determined to be invalid and is not displayed on the display device. 
     
     
         10 . The method of  claim 9 , further including periodically repeating steps (a)-(e). 
     
     
         11 . The method of  claim 10 , wherein, once the sensor data is determined to be valid, said data is transmitted to be displayed on said display device. 
     
     
         12 . The method of  claim 6 , wherein said second threshold is between about 10,000Ω and about 12,000Ω. 
     
     
         13 . A method for determining the validity of glucose sensor data, said glucose sensor including physical sensor electronics, a microcontroller, and a working electrode, the method comprising:
 (a) performing, by said microcontroller, an electrochemical impedance spectroscopy (EIS) procedure to obtain imaginary impedance values for said electrode;   (b) setting a threshold reference for said imaginary impedance values;   (c) calculating a change value as a difference between the threshold reference and the most-recent imaginary impedance value;   (d) obtaining measurements of the calibration factor for said sensor;   (e) comparing, by said microcontroller, said change value to a first threshold and said calibration factor to a second threshold; and   (f) based on said comparison, determining whether said sensor data is valid, such that the sensor can continue to operate, or said data is invalid, such that the sensor should be terminated.   
     
     
         14 . The method of  claim 13 , wherein said imaginary impedance values are 8 kHz imaginary impedance values. 
     
     
         15 . The method of  claim 13 , wherein said threshold reference is calculated as the minimum 8 kHz imaginary impedance value since sensor initialization. 
     
     
         16 . The method of  claim 15 , wherein said threshold reference is clipped so as to fall within the range −1,000Ω and 800Ω. 
     
     
         17 . The method of  claim 13 , wherein said change value is calculated as the absolute difference between the threshold reference and the most-recent imaginary impedance value. 
     
     
         18 . The method of  claim 13 , wherein said first threshold value is 1,200Ω and said second threshold value is 14 mg/dL/nA. 
     
     
         19 . The method of  claim 13 , wherein the sensor data is determined to be valid if either the calibration factor is less than the second lower threshold or the change value is less than the first lower threshold for two consecutive measurements of the change value. 
     
     
         20 . The method of  claim 13 , further including terminating the sensor if the change value is greater than the first threshold for two consecutive measurements of the change value, and the calibration factor is greater than said second threshold. 
     
     
         21 . The method of  claim 13 , wherein the sensor includes a plurality of working electrodes, and steps (a)-(f) are performed for each of the plurality of electrodes.