A novel method to detect pressure-induced sensor attenuations (PISA) in an artificial pancreas

Abstract

Continuous glucose monitors (CGMs) provide real-time interstitial glucose concentrations that are essential for automated treatment of individuals with type 1 diabetes. Miscalibration, noise spikes, dropouts, or pressure applied to the site (e.g., lying on the site while sleeping) can cause inaccurate glucose signals, which could lead to inappropriate insulin dosing decisions. These studies focus on the problem of pressure-induced sensor attenuations (PISAs) that occur overnight and can cause undesirable pump shut-offs in a predictive low glucose suspend system. The algorithm presented here uses real-time CGM readings without knowledge of meals, insulin doses, activity, sensor recalibrations, or fingerstick measurements. The real-time PISA detection technique was tested on outpatient "in-home" data from a predictive low-glucose suspend trial with over 1125 nights of data. A total of 178 sets were created by using different parameters for the PISA detection algorithm to illustrate its range of available performance. The tracings were reviewed via a web-based analysis tool by an engineer with an extensive expertise on analyzing clinical datasets and ~3% of the CGM readings were marked as PISA events which were used as the gold standard. It is shown that 88.34% of the PISAs were successfully detected by the algorithm, and the percentage of false detections could be reduced to 1.70% by altering the algorithm parameters. Use of the proposed PISA detection method can result in a significant decrease in undesirable pump suspensions overnight, and may lead to lower overnight mean glucose levels while still achieving a low risk of hypoglycemia.

Keywords: algorithms; artificial pancreas; continuous glucose monitor; fault detection; hypoglycemia; sensor attenuations.

Figure 1.

In this overnight study there are three periods where a pump shut-off occurred. The third shut-off is due to a PISA event, and was deemed to be an undesirable pump shut-off.^,

Figure 2.

Receiver operating characteristic curve shows the effect of various parameter sets. Inset is the magnified area for better visualization. Larger dots represent various sets of parameters selected for further analysis. Aggressive set has the highest true positive rate while on the other hand; cautious set has the lowest false positive rate. Nominal set has parameters between aggressive and cautious, and the trial set was determined in the region relatively closer to the aggressive and currently being used in a clinical study.

Figure 3.

The effect of each parameter set is shown in individual night continuous glucose monitor (CGM) plots.