Adaptive signal processing for infusion devices and related methods and systems

Abstract

Infusion systems, infusion devices, and related operating methods are provided. An exemplary method of operating an infusion device involves obtaining a filtered measurement indicative of a physiological condition of a user, determining a metric indicative of a characteristic of the filtered measurement based at least in part on one or more derivative metrics associated with the filtered measurement, and determining an output measurement indicative of the physiological condition of the user based at least in part on the filtered measurement, the metric, and a previous output measurement.

What is claimed is: 
     
         1 . An infusion system comprising:
 a sensing arrangement including a sensing element to provide one or more signals corresponding to a physiological condition in a body of a user that is sensed by the sensing element, the sensing arrangement determining an output measurement indicative of the physiological condition based at least in part on a filtered measurement based on the one or more signals, a metric indicative of a characteristic of the filtered measurement, and a previous output measurement; and   an infusion device comprising:
 a motor operable to deliver fluid to the body of the user, the fluid influencing the physiological condition; and 
 a control system to receive the output measurement and determine a delivery command for operating the motor based at least in part on the output measurement. 
   
     
     
         2 . The infusion system of  claim 1 , the sensing arrangement determining a calibration factor for converting the output measurement to a sensed value for the physiological condition, wherein:
 the metric is influenced by the calibration factor; and   the control system determines the delivery command based at least in part on the sensed value.   
     
     
         3 . The infusion system of  claim 2 , the sensing arrangement identifying a dropout condition based at least in part on one or more derivative metrics associated with the filtered measurement and determining a dropout compensated filtered measurement in response to identifying the dropout condition, the output measurement being determined based at least in part on the dropout compensated filtered measurement, wherein the infusion device further comprises a display to present a graphical representation of the sensed value determined based on the dropout compensated filtered measurement. 
     
     
         4 . The infusion system of  claim 2 , the sensing arrangement identifying an artifact condition when a difference between the filtered measurement and a preceding filtered measurement exceeds a threshold value and determining the output measurement by maintaining the previous output measurement in response to the artifact condition, wherein the infusion device further comprises a display to present a graphical representation of the sensed value determined based on the previous output measurement after identifying the artifact condition. 
     
     
         5 . The infusion system of  claim 1 , wherein the sensing arrangement further comprises:
 a first buffer to maintain a plurality of unfiltered measurement values comprising periodically sampled output electrical signals from the sensing element;   a second buffer to maintain a plurality of filtered measurements;   a control module coupled to the sensing element, the first buffer, and the second buffer to:
 determine the plurality of filtered measurements indicative of the physiological condition of the user based on the plurality of unfiltered measurement values; 
 determine a first derivative metric associated with a current filtered measurement of the plurality of filtered measurements and a second derivative metric associated with the current filtered measurement based on the plurality of filtered measurements; 
 determine a process variance metric indicative of a signal characteristic of the current filtered measurement of the plurality of filtered measurements based at least in part on the first derivative metric and the second derivative metric associated with the current filtered measurement; and 
 determine the output measurement based at least in part on the current filtered measurement, the process variance metric, and the previous output measurement; and 
   a communications interface coupled to the control module to transmit the output measurement.   
     
     
         6 . The infusion system of  claim 1 , wherein the metric comprises a process variance metric indicative of a signal characteristic of the filtered measurement. 
     
     
         7 . The infusion system of  claim 6 , wherein the process variance metric is progressively increased when a dropout condition is identified. 
     
     
         8 . The infusion system of  claim 6 , wherein the sensing arrangement determines an error estimate based at least in part on the process variance metric, determines a gain value based at least in part on the error estimate, and determines the output measurement using the equation i out =i out [n−1]+k(i sig −i out  [n−1]), where i out  represents the output measurement, i out [n−1] represents the previous output measurement, and i sig  represents the filtered measurement, and k represents the gain value. 
     
     
         9 . The infusion system of  claim 6 , wherein the sensing arrangement determines the process variance metric based on an estimate of a signal frequency associated with the filtered measurement and an estimate of a signal noise associated with the filtered measurement. 
     
     
         10 . The infusion system of  claim 6 , wherein the sensing arrangement identifies a dropout condition when a first derivative metric associated with the filtered measurement is greater than a first derivative dropout threshold value and a second derivative metric associated with the filtered measurement is less than a second derivative dropout threshold value and modifies the process variance metric in response to the dropout condition. 
     
     
         11 . The infusion system of  claim 1 , wherein the sensing arrangement identifies a dropout condition when a first derivative metric associated with the filtered measurement is greater than a first derivative dropout threshold value and a second derivative metric associated with the filtered measurement is less than a second derivative dropout threshold value and modifies the filtered measurement in response to the dropout condition. 
     
     
         12 . The infusion system of  claim 11 , wherein the sensing arrangement modifies the filtered measurement by adding an offset to the filtered measurement to obtain an adjusted filtered measurement and determines the output measurement based at least in part on the adjusted filtered measurement, the metric indicative of the characteristic of the filtered measurement, and the previous output measurement. 
     
     
         13 . An infusion system comprising:
 a sensing device comprising:
 a sensing element to provide one or more signals influenced by a physiological condition of a user; 
 a control module coupled to the sensing element to:
 determine a filtered measurement based on the one or more signals; 
 determine a process variance metric indicative of a signal characteristic of the filtered measurement based at least in part on one or more derivative metrics associated with the filtered measurement; and 
 determine an output measurement indicative of the physiological condition of the user based at least in part on the filtered measurement, the process variance metric, and a previous output measurement; and 
 
 a communications interface coupled to the control module to transmit the output measurement; and 
   an infusion device comprising:
 a motor operable to deliver fluid to the user, the fluid influencing the physiological condition; and 
 a control system to receive the output measurement and determine a delivery command for operating the motor based at least in part on the output measurement. 
   
     
     
         14 . The infusion system of  claim 13 , wherein:
 the sensing device further comprises:
 a first buffer to maintain a plurality of unfiltered measurement values comprising periodically sampled output electrical signals from the sensing element; and 
 a second buffer to maintain a plurality of filtered measurements; and 
   the control module is coupled to the first buffer and the second buffer to:
 determine the plurality of filtered measurements indicative of the physiological condition of the user based on the plurality of unfiltered measurement values; 
 determine a first derivative metric associated with a current filtered measurement of the plurality of filtered measurements and a second derivative metric associated with the current filtered measurement based on the plurality of filtered measurements; and 
 determine the process variance metric based at least in part on the first derivative metric and the second derivative metric associated with the current filtered measurement. 
   
     
     
         15 . The infusion system of  claim 13 , wherein operation of the infusion device to regulate the physiological condition of the user is influenced by the output measurement. 
     
     
         16 . An infusion system comprising:
 a sensing arrangement comprising:
 a sensing element to output electrical signals are influenced by a physiological condition in a body of a user; 
 a first buffer to store a plurality of unfiltered measurement values comprising periodically sampled output electrical signals from the sensing element; 
 a second buffer to store plurality of filtered measurements indicative of the physiological condition of the user; 
 a communications interface to transmit an output filtered measurement; and 
 a control module coupled to the sensing element, the first buffer, the second buffer, and the communications interface to determine the plurality of filtered measurements indicative of the physiological condition of the user based on the plurality of unfiltered measurement values, determine a first derivative metric associated with a current filtered measurement of the plurality of filtered measurements and a second derivative metric associated with the current filtered measurement based on the plurality of filtered measurements, determine a process variance metric indicative of a signal characteristic of the current filtered measurement based at least in part on the first derivative metric and the second derivative metric, and determine the output filtered measurement indicative of the physiological condition of the user based at least in part on the current filtered measurement, the process variance metric, and a previous output measurement; and 
   an infusion device to receive the output filtered measurement, wherein operation of the infusion device to deliver fluid to the body of the user is influenced by the output filtered measurement.   
     
     
         17 . The infusion system of  claim 16 , wherein the control module determines a frequency estimate associated with the current filtered measurement based on the first derivative metric, determines a noise estimate associated with the current filtered measurement based on the second derivative metric, and determines the process variance metric as a function of the frequency estimate and the noise estimate. 
     
     
         18 . The infusion system of  claim 17 , wherein the control module determines the frequency estimate by scaling the first derivative metric by a calibration factor for converting the output filtered measurement to a sensed value for the physiological condition and determines the noise estimate by scaling the second derivative metric by the calibration factor. 
     
     
         19 . The infusion system of  claim 16 , wherein the control module identifies a dropout condition based at least in part on one or more of the first derivative metric or the second derivative metric associated with the current filtered measurement and modifies at least one of the current filtered measurement or the process variance metric in response to identifying the dropout condition. 
     
     
         20 . The infusion system of  claim 16 , wherein the infusion device comprises a motor operable to deliver the fluid to the user and a control system to determine a delivery command for operating the motor based at least in part on the output filtered measurement.