Glucose sensor health monitoring and related methods and systems

• US 10,152,049 B2
• Filed: 05/19/2014
• Issued: 12/11/2018
• Est. Priority Date: 05/19/2014
• Status: Active Grant

• Current Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Original Assignee: Medtronic Minimed Incorporated (Medtronic Plc)
• Inventors: Nogueira, Keith, Li, Xiaolong, Shah, Rajiv, Kannard, Brian T.
• Primary Examiner(s): Betsch, Regis
• Application Number:
  US14/281,773
• Publication Number:
  US 20150331419A1
• Time in Patent Office: 1,667 Days
• CPC Class Codes: A61M 2205/70 with testing or calibration facilities
• CPC Class Codes: A61M 2205/702 automatically during use
• CPC Class Codes: A61M 2230/201 Glucose concentration
• CPC Class Codes: A61M 5/14244 adapted to be carried by the patient, e.g. portable on the body
• CPC Class Codes: A61M 5/1723 using feedback of body parameters, e.g. blood-sugar, pressure measurement of body parameters A61B5/00
• CPC Class Codes: G05B 23/00 Testing or monitoring of control systems or parts thereof monitoring of programme-control systems G05B19/048, G05B19/406

Abstract

Infusion systems, infusion devices, and related operating methods are provided. An exemplary method of operating an infusion device capable of delivering fluid to a user involves determining one or more signal characteristics associated with a subset of the measurements corresponding to a monitoring period, determining a reliability metric for the monitoring period based on the one or more signal characteristics, and providing indication of a maintenance condition when the reliability metric violates a threshold.

Claims

1. A method of providing indication when replacement of an interstitial glucose sensing element of a sensing arrangement should be performed in connection with operating an infusion device operable to deliver fluid to a user based on measurements indicative of an interstitial fluid glucose level of the user provided by the sensing arrangement, the fluid influencing the physiological condition of the user, the method comprising:

obtaining, by a control module coupled to the interstitial glucose sensing element of the sensing arrangement, a plurality of uncalibrated measurements corresponding to a monitoring period based on output signals provided by the sensing element, wherein the output signals are influenced by the interstitial fluid glucose level of the user;

obtaining, by the control module, a calibration factor for converting the plurality of uncalibrated measurements to a plurality of calibrated measurement values for the physiological condition;

for each respective measurement of the plurality of uncalibrated measurements;

determining a second derivative metric associated with the respective measurement based at least in part on a difference between a first derivative metric associated with the respective measurement and the first derivative metric associated with the preceding measurement of the plurality of uncalibrated measurements, wherein the second derivative metric associated with a most recent measurement of the plurality of uncalibrated measurements comprises the greater of a difference between the first derivative metric associated with the most recent measurement and the first derivative metric associated with the immediately preceding measurement of the plurality of uncalibrated measurements and an average magnitude of second derivative metric values associated with the plurality of uncalibrated measurements; and

scaling the second derivative metric associated with the respective measurement by the calibration factor to determine a noise metric for the respective measurement of the plurality of uncalibrated measurements;

determining, by the control module, a number of high noise measurements for the monitoring period based on the noise metrics for the respective measurements of the plurality of uncalibrated measurements;

determining, by the control module, an output measurement value indicative of the interstitial fluid glucose level based at least in part on the most recent measurement of the plurality of uncalibrated measurements and at least one of the first derivative metric associated with the most recent measurement and the second derivative metric associated with the most recent measurement;

transmitting, by a communications interface coupled to the control module, the output measurement value to the infusion device, wherein a delivery command for operating a motor of the infusion device to autonomously control delivery of the fluid to the user is determined based at least in part on the output measurement value and the calibration factor; and

providing, via an output interface of the sensing arrangement, indication replacement of the interstitial glucose sensing element should be performed when a reliability metric influenced by the number of high noise measurements violates a first threshold.

2. The method of claim 1, further comprising determining a number of consecutive monitoring periods that violated the first threshold when the number of high noise measurements for the monitoring period violates the first threshold, wherein providing the indication comprises automatically providing the indication when the number of consecutive monitoring periods is greater than a second threshold.

3. The method of claim 1, further comprising:

determining an average measurement value for the monitoring period based on the plurality of uncalibrated measurements; and

determining the reliability metric based at least in part on a ratio of the average measurement value to the number of high noise measurements.

4. The method of claim 3, further comprising determining a second number of consecutive monitoring periods that violated the first threshold when the reliability metric for the monitoring period violates the first threshold, wherein providing the indication comprises providing the indication when the second number of consecutive monitoring periods is greater than a second threshold.

5. The method of claim 1, wherein determining the number of high noise measurements comprises determining the number of respective measurements of the plurality of uncalibrated measurements having an associated noise metric greater than a threshold value.

6. The method of claim 5, further comprising determining a second number of consecutive monitoring periods that violated the first threshold when the reliability metric for the monitoring period violates the first threshold, wherein providing the indication comprises providing the indication when the second number of consecutive monitoring periods is greater than a second threshold.

7. A non-transitory computer-readable medium having computer-executable instructions stored thereon that, when executed by the control module, cause the control module to perform the method of claim 1.

8. The method of claim 1, further comprising:

periodically sampling the output signals of the interstitial glucose sensing element to obtain a plurality of unfiltered measurement values stored in an unfiltered sample buffer;

periodically obtaining a plurality of unfiltered measurement values from the unfiltered sample buffer;

applying a filter to the plurality of uncalibrated measurements to obtain a filtered measurement; and

storing the filtered measurement in a filtered sample buffer, wherein obtaining, the plurality of uncalibrated measurements corresponding to the monitoring period comprises obtaining the plurality of uncalibrated measurements from the filtered sample buffer.

9. The method of claim 1, wherein obtaining the plurality of uncalibrated measurements comprises obtaining a plurality of five-minute filtered measurement values.

10. The method of claim 9, further comprising:

periodically sampling the output signals of the interstitial glucose sensing element on a per-minute to obtain a plurality of unfiltered measurement values stored in an unfiltered sample buffer; and

periodically obtaining the plurality of unfiltered measurement values from the unfiltered sample buffer every five minutes;

applying a filter to the plurality of unfiltered measurement values obtained from the unfiltered sample buffer to obtain the respective five-minute filtered measurement values of the plurality of five-minute filtered measurement values.

11. The method of claim 10, wherein the first derivative metric associated with each respective measurement of the plurality of uncalibrated measurements comprises a difference between a respective five-minute filtered measurement value and an immediately preceding five-minute filtered measurement value.

12. The method of claim 11, further comprising:

converting the most recent measurement into a sensed glucose value using the calibration factor; and

determining the delivery command for operating the motor of the infusion device to deliver the fluid to the user based at least in part on the sensed glucose value.

13. The method of claim 1, wherein determining the delivery command comprises:

converting the most recent measurement into a sensed glucose value using the calibration factor; and

determining an insulin dosage command based at least in part on a difference between the sensed glucose value and a target glucose value.

14. The method of claim 13, further comprising operating the motor of the infusion device to achieve the insulin dosage command.

15. An infusion system providing indication when replacement of an interstitial glucose sensing element should be performed, the interstitial glucose sensing element providing output signals influenced by an interstitial fluid glucose level in a body of a user, the infusion system comprising:

a communications interface; and

a control module coupled to the interstitial glucose sensing element and the communications interface to determine a plurality of uncalibrated filtered measurements based on the output signals, determine one or more noise metrics associated with a subset of the plurality of uncalibrated filtered measurements corresponding to a monitoring period based at least in part on a calibration factor for converting the plurality of uncalibrated filtered measurements to a plurality of calibrated measurement values for the physiological condition, determine a reliability metric for the monitoring period based on the one or more noise metrics, determine an output measurement value indicative of the interstitial fluid glucose level based at least in part on a most recent measurement of the subset and at least one of a first derivative metric associated with the most recent measurement and a second derivative metric associated with the most recent measurement, transmit the output measurement value to an infusion device via the communications interface, and provide indication for replacement of the sensing element when the reliability metric violates a first threshold, wherein;

a delivery command for operating a motor of the infusion device to autonomously control delivery of a fluid influencing the interstitial fluid glucose level to the user is determined based at least in part on the output measurement value and the calibration factor;

the one or more noise metrics comprise a respective noise metric for each respective uncalibrated filtered measurement of the subset and an average measurement value of the subset of the plurality of uncalibrated filtered measurements for the monitoring period;

the respective noise metric for each respective uncalibrated filtered measurement comprises a second derivative metric associated with the respective uncalibrated filtered measurement scaled by the calibration factor;

the second derivative metric associated with the most recent measurement of the subset comprises the greater of a difference between the first derivative metric associated with the most recent measurement and the first derivative metric associated with an immediately preceding measurement of the subset and an average magnitude of the second derivative metric values associated with the subset;

the reliability metric comprises a ratio of the average measurement value to a number of high noise measurements over the monitoring period; and

the number of high noise measurements comprises a number of filtered measurements of the subset having respective noise metrics that violate a second threshold.

16. The infusion system of claim 15, further comprising an output user interface element coupled to the control module, wherein providing the indication comprises the control module generating a user notification indicating replacement of the sensing element when the reliability metric violates the first threshold.

17. The infusion system of claim 15, wherein the control module determines a second number of consecutive monitoring periods that violated the first threshold when the reliability metric for the monitoring period violates the first threshold and automatically provides the indication when the second number of consecutive monitoring periods is greater than a third threshold.

18. A method of providing indication when replacement of an interstitial glucose sensing element should be performed in connection with operating an infusion device operable to deliver insulin to a body of a user, the method comprising:

determining, by a control module coupled to the interstitial glucose sensing element, a plurality of uncalibrated filtered measurements indicative of an interstitial fluid glucose level in the body of the user based on output signals from the interstitial glucose sensing element, wherein the output signals are influenced by the interstitial fluid glucose level in the body;

obtaining, by the control module, a calibration factor for converting the plurality of uncalibrated filtered measurements to a plurality of calibrated sensor glucose values;

for each respective filtered measurement of the subset;

determining a second derivative metric associated with the respective filtered measurement of the subset based at least in part on a difference between a first derivative metric associated with the respective filtered measurement and the first derivative metric associated with the preceding filtered measurement of the subset, wherein the second derivative metric associated with a most recent filtered measurement of the subset comprises the greater of a difference between the first derivative metric associated with the most recent filtered measurement and the first derivative metric associated with the immediately preceding filtered measurement of the subset and an average magnitude of second derivative metric values associated with the subset;

scaling the second derivative metric associated with the respective filtered measurement by the calibration factor to determine a respective noise metric associated with the respective filtered measurement of the subset;

determining, by the control module, a number of high noise measurements during the monitoring period as a number of respective filtered measurements of the subset having an associated noise metric greater than a threshold value;

determining, by the control module, a reliability metric for the monitoring period as a ratio of an average measurement value for the monitoring period to the number of high noise measurements during the monitoring period;

determining, by the control module, an output measurement value indicative of the interstitial fluid glucose level based at least in part on the most recent measurement of the subset and at least one of the first derivative metric associated with the most recent measurement and the second derivative metric associated with the most recent measurement;

transmitting, by a communications interface coupled to the control module, the output measurement value to the infusion device, wherein a delivery command for operating a motor of the infusion device to autonomously control delivery of the fluid to the user is determined based at least in part on the output measurement value and the calibration factor; and

providing, via an output interface, a user notification to replace the interstitial glucose sensing element when the reliability metric violates a first threshold.

19. The method of claim 18, further comprising determining a second number of consecutive monitoring periods having an associated reliability metric less than the first threshold when the reliability metric for the monitoring period is less than the first threshold, wherein providing the user notification comprises automatically providing the user notification when the second number of consecutive monitoring periods is greater than a second threshold.