[elmin]

Can someone explain why notifying the device of exercise and eating is necessary? Is it because 5 minutes is too low of an interval, or because the glucose sensor is slow, or because the body relies on other eating and exercise cues to regulate insulin.

[shanselman]

Because if you start exercising or eating NOW the insulin administered won't start working for 30 min and won't peak for 90-120 minutes. Because food hits you fast and by the time the system notices you'll have already drifted "out of the lanes."

Diabetes Closed Loops are the same problem as controlling the Mars Rover. You move the joystick and nothing happens for x minutes. Then you wait another x minutes to observe the results.

[cperciva]

The sensors aren't perfectly accurate; I don't know about the newer sensors which this closed-loop system uses, but the current generation only fulfills the accuracy requirements by reporting the median of 7 consecutive every-5-minutes measurements and carrying a warning of "don't trust these values if you have reason to think that your blood glucose might be changing rapidly".

My guess is that providing notifications of exercise and food (aka. "I expect my blood glucose to go (down|up) right now") allows the model to be tuned to respond more aggressively to new data at some times and less aggressively at others.

(The "less aggressively" side is probably most important: If the sensor suddenly reports a dramatic change in blood glucose in the middle of the night, the system should probably respond with "HEY WAKE UP THE SENSOR IS BROKEN" rather than "let's kill the patient".)

[shanselman]

Exactly. Not to mention they are testing interstitial fluid and not whole blood, which introduces significant delays.

[cperciva]

I've found that the interstitial delay is pretty minimal; maybe 5-10 minutes behind fingerpricks (which themselves lag somewhat behind arterial blood, especially if your hands are cold). The dominating factor is the 15-20 minutes it takes before the median of a window reflects the new data.

[shanselman]

Sure, but we agree every minute counts. Also, CGMs in arms differ from belly, etc. 10 min when insulin starts in 30 is a non-trivial amount of time. Point is, we def need faster insulin and faster, more accurate CGMs.

[kellyisworking]

A couple things - the insulin currently on the market works too slowly for a pump right now to fully close the loop – this functionality – notifying the pump of exercise and eating is part of the user control needed in a "hybrid closed loop" such as this. The user's insulin sensitivity given before, during or after exercise are very different than at other times. Different types of exercise affects body differently as well –HIIT for example raises blood glucose for a couple hours during and after – and then will significantly increase the sensitivity to insulin and many type 1's will drop rapidly. Aerobic activity will tend to drop blood glucose rapidly on it's own. Notifying the pump allows you to drop the levels given – something users do on their own now.