So this is an open thread on how open APS works, what it’s like to use it, for those who are interested. Ask any questions here – and those who are using openAPS or Loop and are more knowledgeable than me can hopefully chime in with their experience, too!
Some background: Our two-year-old son is using openAPS using a raspberry Pi as the minicomputer that communicates between the Dexcom CGM and the Minimed 522 pump. The algorithm is a fairly simple predictive model. Other people may have other hardware setups.
As I understand it (and DISCLAIMER I am NOT the one who coded it, so I could be wrong in the details), it looks at three of the past data points (or roughly 15 minutes) to get a rate of change that will help predict where blood sugar will be in the future. EDITED TO CORRECT: While it does look at three data points sometimes to potentially veto a decision the algorithm would have made, most of the time it relies on the current BG reading and the amount of IOB
Based on that, it issues temporary basal rates of half-hour duration, either high, low or zero, to try to keep you within your target range. If your raspberry Pi loses communication with the pump or the CGM, after 30 minutes, that temp basal automatically expires. If no CGM data has shown up over 15 minutes, then the system will not issue a temp basal and will (assuming it has not lost communication with the pump) cancel the temp basal and default to your basal settings. There is a MaxSafeBasal which you can set yourself, which helps determine how much insulin you’re willing to let the automated system send assuming that either it’s wrong or will lose connection at any time. The system does not issue boluses.
there are other features, such as an auto-sensitivity and Advanced Meal Assist mode, which we’ve just set up and I can try to explain, but to be honest we still don’t totally grasp the nuances of that system.
So ask away!