Background and Aims
Do-It-Yourself (DIY) algorithms for closed-loop insulin delivery are increasingly popular but infrequently studied in humans, outside of observational studies, due to lack of regulatory approval. We therefore conducted studies in pigs comparing AndroidAPS and Loop without meal announcement, leveraging faster insulin pharmacokinetics inherent to swine.
Pigs with streptozocin-induced diabetes were started on AndroidAPS running oref1 (with super-microbolus enabled) and Loop (with integral retrospective correction enabled). Insulin dosing including basal rate, insulin-to-carbohydrate ratio (ICR) and insulin sensitivity factor (ISF) were determined clinically prior to closed-loop initiation. Insulin pharmacokinetics were derived by ELISA and observation of glucose dynamics. Basal rate testing was conducted overnight without insulin-on-board (IOB) or carbs-on-board (COB) and rates were titrated to maintain glucose. ISF was calculated by administering 1 unit insulin under hyperglycemic conditions with no IOB or COB. ICR was calculated and then titrated such that post-meal blood sugar matched pre-meal.
6 pigs were started on AndroidAPS followed by Loop. Insulin pharmacokinetics are more rapid in pigs with peak serum concentrations within 20-25 minutes and near complete absorption by 2 hours, modeled in both systems. In total, there were 23 days of AndroidAPS and 18 days of Loop data. Time-in-Range (70-180mg/dL) was significantly greater (p < 0.001) with AndroidAPS (63.7 ± 13.4%) versus Loop (40.5 ± 17.2%).
For unannounced meals, Time-in-Range was greater with AndroidAPS than with Loop. oref1 with super-microbolus is designed for unannounced meals, whereas Loop is a model predictive controller with short-term adaptation more dependent on meal data.