For starters, to me (and I DO use C-IQ) IOB is probably the third most important thing that I look at: First is current glucose level, second is trend arrow (or the 3-hr plot), but number three is IOB. If my glucose level is 130 mg/dl but dropping, I take very different actions if I have IOB = 0 (where I probably just let C-IQ dial back my basal) versus IOB = 2 units where I will definitely eat something.
Also, aside from the missing remaining time, IOB tells me the same thing regardless of whether I run C-IQ or not. In either case it is now much remaining active insulin do I have to bring down BG levels.
Why doesn’t C-IQ show the remaining time for IOB any more? I think that is because with automatic increases in basal rate, it is hard to define the end point. For starters, with a simple bolus of, for example, 5 units it is easy. Note: I am assuming that Tandem linearly tapers IOB over time. They may use a different curve, but if they do, the principle is the same, the math is just trickier.
So, under the linear decay of IOB assumption, 5 unit bolus would 5 U of IOB at bolus completion, 4 U of IOB after 1 hour, 3 U of IOB after 2 hours, 2 U of IOB after 3 hours, 1 U of IOB after 4 hours and 0 U of IOB after 5 hours. We all agree on that (assuming linear decay), correct?
Now, suppose in addition to that 5 U bolus at time = 0, C-IQ increases the basal by 0.1 U at time = 1 hours, another 0.1 U at 1 hr 30 minutes, a third 0.1 U at 2 hours, a fourth 0.1 U at 2 hr 30 minutes, and a fifth 0.1 U at 3 hours. Each of those additional 0.1 U will begin to “decay” by 0.02 U/hr (assuming linear decay) but all starting at different points in time.
I put that into an Excel spread sheet and plotted IOB versus time.
Here is what it looks like:
You can see that it has the initial steep decay due to the original 5 U bolus, but a long, gradual “tail” as each of the C-IQ added bits decay and timeout. So, after 5 hours the IOB is down to 0.2 U, but it doesn’t actually reach zero until 8 hours (5 hours after the last 0.1 increased bolus). So, while we can probably agree that the IOB ends somewhere between 5 and 8 hours after the initial bolus in this example, it is probably hard to define that actual end point … particularly if there was another C-IQ added bit of basal fairly late in this decay.
As a result, Tandem is doing the complex IOB calculation for us, but I suspect (I have no “insider information”) chose not to show the remaining time, because it is hard to define when you could have a significant series of “mini-boluses” over time.
At least that is my opinion.
Stay safe!
John