So the active insulin time (DIA) is basically the time, from when the injection of insulin is made, till when the last bit working in the body to lower blood sugar gets used up.
When you inject the insulin, it has to travel through your fat, your interstitial tissue, into blood vessels, and then make its loop-de-loop through the body before it reaches your tissue and starts working. Once it’s in your bloodstream I believe it’s only active for about 4 minutes, but there’s a pool of insulin that’s sitting in your body but NOT YET in your blood stream that has yet to be put to use for several hours after injection.
Studies have shown that it’s typically in the 5 to 6 hours range for the vast majority of people. In other words, there’s usually some insulin sitting near your pump infusion site inside your body, but not yet in your bloodstream, for about 6 hours.
The reason it’s important is that it can prevent insulin stacking. I.e. let’s say you’re blood sugar is high and you think you need 2 units to bring it down. If your active insulin time is 2 hours, you may underestimate how much is still there later, and may have unanticipated lows.
Practically speaking, you can super roughly estimate that about 20 to 25 percent of the insulin you inject is going to be active each hour. (The amount that gets used up doesn’t go linearly and actually there’s a time of “peak insulin action” which is roughly an hour or 1.5 hours after injection, but as a very rough ballpark it’s useful to think of it like this for me).
Also practically speaking, with newer systems this DIA that you program is JUST A KNOB that you can dial up or down to make your system more aggressive or more conservative. It has a rough physical analog but I don’t think the settings you program in are necessarily going to work best if they correspond to the underlying physiological reality. Does that make sense?