Terminology: the "Closed Loop"

There’s an emerging “loop” usage that is, to my mind, going to become confusing and therefore the source of heated misunderstanding and debate. Back in October 2017 on FUD the term “Hybrid Closed System” was used for emerging Tandem pumps. The systems would close the loop between BG and Insulin automagically, but only so long as the user of the system rigorously bolused for carbs. The closed loop picks up the inevitable errors and corrects for them.

Almost at the same thing a term full closed loop appeared to fill in the gap; what, after all, is a closed loop system that is not “hybrid”. A full closed loop system is a system where the user does not either bolus or record carbs. Everything else is hybrid because we provide some assistance, entering carbs and even bolusing (or, as FUD prefers, blousing) for them.

It’s not a defined usage and therefore it’s not an accepted usage; it’s not in my several copies of Websters or Collins so it’s a source of dispute and will certainly benefit none of us. So we have to argue and decide and then the language will mean what we say:

Hybrid Closed Loop: a system where an automated insulin delivery system augmented with blood glucose measurement assists a person needing insulin by responding to higher or lower blood sugar by adjustments to insulin delivery.

Full Closed Loop: a system where an automated insulin delivery system augemented with blood glucose measurement delivers insulin without additional input to maintain the user’s blood glucose levels within desired ranges.