Loop -- a dynamic answer to a dynamic problem


So that morning rise is unpredictable? You aren’t administering fake carbs every day?


The morning rise is fairly predictable. I’ve found that I need to use the fake carb tactic almost every day. But I do not need to execute this tactic until my feet hit the floor in the morning. I don’t get up at the exact same time every day, so programming in a pre-emptive pump basal rate could end up driving me low in my last 30-60 minutes of sleep, when I sleep a little longer.


Ah - I see. That’s the clincher.


Has anyone tried to simulate a Super Bolus with these setups? Would using an absorption rate of immediately replicate a front loading of insulin delivery?


I have heard of someone linking their smartwatch to the Loop–thereby signaling when you wake-up–thus dynamically initiating the “wake-up” insulin routine.


That’s something that’s been done with OpenAPS rather than Loop. Dana set hers up to pick that up. I just set a higher basal rate ahead of when I’m going to get up, and let the loop lower the basal if it sees that what is set is incorrect.


Terry (and others)! That first night of Looping gave me a false sense of success! We’ve only added one more night to the experience, but things did not go as smoothly.

I’m generally seeing highs. Either he goes high after a meal or he levels off and then just goes high bc Loop is overcompensating for IOB. My traditional pump mind thinks its a DIA problem, but I’m thinking (and hearing) this may have everything to do with ISF.

So I understand that if your ISF is too high (meaning delivers a more aggressive bolus) then Loop will compensate and turn off basal and the high will result. So this seems to mean if I adjust too much in the opposite direction, Loop won’t compensate enough, and it will result in lows.

So I can’t use the mama bed or the papa bed, I need the baby bed to fit just right. Am I at all making Loop sense?


So, you know you need to add more insulin or better match the time profile the carbs need. Are you prebolusing a standard time you’ve found works? Have you done a prebolusing mini-experiment and “wait for the bend”?

You’re right about a high IOB dampening the ability of Loop to high-temp. If you change your ISF so that more insulin is called for when trending higher. The duration of insulin action (DIA) also drives the IOB number. I have mine set at 4 hours 30 minutes, but that may not be yours.

You’re an old pro at this but I find communication about ISF can be confusing due to the inverse relationship. In other words, 1:30 will deliver more of a correction than 1:40 and that’s what you want.

You might also look at the max basal rate you’ve set in both the pump and Loop app. This is a custom number. You may need to increase the Loop’s ability to amp up the high-temp basal to be effective.

I am still very much in learning mode, so my experience is not definitive. Good luck!


Hi @Lorraine, what we’ve found is that yes, ISF plays a role but not as big as you’d think. The other thing we’ve found (which may not apply to your guy) is that the idea basal rate we set is not necessarily exactly what would be needed to prevent our son from going low in the long absence of food for several hours. Because Loop (or openAPS) is using ISF and basal rate in every calculation every five minutes, It’s really just this interplay of all three factors, and I suspect you could come up with some combination of parameters that works well even if they’re radically different.

The easiest one to test, I think, is the DIA. What we found when we were initially testing out the right DIA was if the DIA was too long, and we gave a bolus, openAPS would shut off too soon, so his BG would start to go down and then, sometime between the three- or four-hour mark (or four- or 5-hour, or 5- or 6-hour, depending on what you set the DIA as) you see it get stuck or edge back up. I’d see it keep trying to nudge down but it just never accomplished that task. Ideally, once you’re four or five hours out from food, the basal you set should be mostly running without a lot of interference from openAPS. But if it’s constantly turning on and off, that can be a sign that the DIA is wrong. Or at least, it was for us, YMMV.

With ISF we basically found that the best way to identify that is a situation where, say, he starts rising for whatever mystery reason, and then somewhere between two and four hours later he goes low. That means that the insulin being delivered by the Loop is too high. However, it’s tricky because this can also occur if the basal rate is too high as it’s determining the high temp by assuming a baseline basal rate would keep BG constant. For this, we increased ISF by 5 points until we stopped seeing lows (or decreased by 5 points until we stop seeing highs). Once it’s close to the mark, we’ll change by 2 or 3.

The biggest factor we’ve found is the basal rate. For us, this just has a huge effect. I’m not sure if it’s because he’s just so little and he has a particular set of parameters, or because basal is actually delivering more than you think (i.e. 0.25/hr actually leads to a peak insulin level of more than 0.25 units), or because the way the algorithm is using basal for determining high- and low-temps has an outsize impact. But for us, a nudge of 0.025/hr up usually leads to a persistent high becoming a stable line or even a low. The only exception to this is the nighttime growth-hormone peak. That just comes on so quickly we found giving a bolus once he falls asleep works better than the gradual accumulation of insulin created by a basal setting.

I’d also second @Terry4’s suggestion to evaluate MaxSafeBasal…if you see the Loop maxing out how much it’s giving (so, for instance, you’ve set the maxSafeBasal to 2 units per hour and it is routinely hitting this), then that’s an indication that if you want Loop to be more on autopilot you need to give it more power, with a higher basal ceiling.
Does that make sense?


@Lorraine, when I look at what openAPS does most of the time, I’d say that when it’s working optimally, most of the time it IS doing a superbolus. Basically, if I give more insulin on the front-end, openAPS will turn off for a few hours and then you wind up with a smoother, lower spike but the same net insulin delivered. So if his oatmeal actually needs 1.8 units to be covered, I might give 2 units up front knowing that it can easily take away the extra from his 0.2 units/hr basal for the next three hours.

Of course it also helps tamp down some of those random daytime spikes from who-knows-what, but I would say that hour-by-hour, most of what it’s doing is turning mealtime boluses into superboluses.


Correct settings are the key. You need to adjust during several days (weeks)… carbs, insulin sensitivity, duration etc.
I’ve been looping for 7 months now, and I’m still not fully tuned.


Also I’d say I reevaluate my settings every two or three days. If I let it go longer than that, we find repeated highs or lows that could have been avoided.



I’ve always known what I try to explain to people who are first diagnosed is probably a little overwhelming. I am now experiencing what I’m sure these newbies I speak to feel. I know (really, I know although it only feels like hope at the moment) that this will indeed become more intuitive to me, but I gotta say, it’s not right now. Our deeply ingrained habits are fighting against the new Loop paradigm, and I’m not exactly sure where to start.

But we now have three days under our belt so we are that much closer to understanding this. Yes, I actually understand what you are saying, but to really appreciate it, I need to see it in action and start fiddling and getting more experience.

We were just celebrating the success of switching to Novolog and Caleb’s number’s being 81% in range with the smallest SD he’s ever had and we just threw it all up in the air and are starting over.

Thanks so much for taking the time to walk me through these things.


Not sure if I understood this statement correctly, so let me go over ISF. Apologies if this has all been clear already: a high ISF [(mg/dL)/U] means that it takes less insulin to correct for a bg that is away from a target. As an example, suppose that Loop predicts eventual bg = 150 mg/dL, that the target is 100 mg/dL, and that ISF = 50 (mg/dL)/U. Then Loop would calculate that (150-100)/50 = 1 U is required as a correction, and would issue a temp basal of +2 U/h above the normal basal rate, in order to deliver the required correction over the next 30 minutes. If, however, ISF were higher, say ISF = 100 (mg/dL)/U, only 0.5 U would be required, and the temp basal command would be +1 U/h. In general, the higher the ISF is, the less aggressive Loop (or OpenAPS) is. Conversely, a lower ISF results in more aggressive operation of the closed-loop system.

A good starting point for ISF would be the value you’ve used for manual corrections. With Loop, one approach I’ve used to make adjustments was to look at overnight performance first. A too low ISF tends to result in overnight oscillations - high temp followed by low temp followed by high temp etc. Fortunately, the resulting bg oscillations tend to be relatively small in amplitude, so that’s not so bad, but it’s a good way to see that ISF is too low. A too high ISF tends to result in bg staying away from the target for too long. A good ISF should result in bg soft landing into target range overnight. In my case, I moved ISF up compared to what I thought was a good value prior to looping. The above description assumes the overnight basal rate is generally set correctly, which can be verified by taking notes of how much extra insulin the Loop delivered (or subtracted) overnight (over at least a few days - I’d not rush to make adjustments to default basal rates).

DIA is also important for Loop operation. I started with a shorter (3 hour) DIA, which I had used in manual operation. Extended that to 4.5 hours, and have had better overall results since. As usual YDMV, but I do not think insulin absorption is that much different from person to person. A DIA of 4 hours or more seems to be more consistent with published curves for the fast acting insulins available today.

Another important factor and (in my experience) the most difficult one is the carb absoption time, which of course depends on the meal type, but also varies a lot from person to person (and time of day, etc), so it is virtually impossible to give any general guidelines. For example, the Loop defaults of 120, 180 and 240 minutes are not working so well for me. For fast carbs, I’d use 90 minutes, while for a complex meal I’d enter a carby portion as 120 min and the rest as up to 360 min. I’d bolus for the first part, and let Loop high temp for the second (which is where max temp basal setting also plays a role). I should note that OpenAPS algorithm called oref0 deals with carb absorption differently.

When I started looping (OpenAPS, then Loop) more than a year ago, I first focused on the nighttime, and I made adjustments to the overnight basal rates and the ISF to get consistent performance. During that time, I kept the system mostly open-loop during day, and continued to surf manually, with closed-loop tests done whenever convenient - trying out different meal absorption times and different carb ratios. It took me a few weeks to get the settings and the absorption times to work well for me.

I’d not be discouraged by some setbacks - there is a lot to learn and do with DIY closed-loop systems. The experience is very different from what we’ve been used to do manually. Best luck!


If you are interested in DIY closed-loop systems, you may look into joining The Looped Group on Facebook.


What’s “the bend” @Terry4?

Yes. I never know how to use “Higher” or “lower” bc of this inversity. I tend use use aggressive/conservative.

I’m glad you raised this. I was focusing on DIA and ISF first. I will think more about basal. When Caleb is little, basal was a huge, huge issue. I guess everything was a huge issue bc he was so sensitive when he was a smaller person. But basal was pretty critical. I wonder if that’s why it’s so apparent for you now.

Yes. Can you set max basal too high? I have it at 15 units![quote=“Tia_G, post:171, topic:57501”]
I might give 2 units up front knowing that it can easily take away the extra from his 0.2 units/hr basal for the next three hours.

Right. That becomes obvious pretty quickly when you move from theory to practice - at least for me it did. Do you think playing with the food absorption rate can put the super bolus reaction into high gear?

Are you using Autotune?[quote=“Dragan1, post:175, topic:57501”]
I moved ISF up compared to what I thought was a good value prior to looping.

I feel like we have to do the same. [quote=“Dragan1, post:175, topic:57501”]
A DIA of 4 hours or more seems to be more consistent with published curves for the fast acting insulins available today.

I agree that this is true. I struggle though, bc I don’t think the duration is on a straight line basis. This is an area I have expected I need to play with.

This is a good idea - to focus on one piece at a time. I’m impatient. I want it all NOW! lol[quote=“Dragan1, post:175, topic:57501”]
I’d not be discouraged by some setbacks - there is a lot to learn and do with DIY closed-loop systems. The experience is very different from what we’ve been used to do manually. Best luck!

Thank you!


“Waiting for the bend” is a term coined by Stephen Ponder in his Sugar Surfing book. A CGM is needed to watch for this effect. It simply means taking a meal dose of insulin and waiting for a clear and marked decline in the blood sugar CGM trace before starting to eat. The idea is to match observed insulin action to eating and the blood sugar rise that follows. This is how I discovered that my ideal morning pre-bolus time is often a full 60 minutes.

By the way, I upgraded to Loop V1.3.0 last Friday. I’ve got a better handle on the whole process but mastery is still in my future.


Holy cannoli. Prebolusing was very important for Caleb when he was little. When he started Apidra, the need almost vanished. I find if we wait for that bend, unless he started with a high bg, we end up in trouble with a low before the food hits. An hour would be a disaster for Caleb. This is something I’ll think about!

We updated too. Haven’t been able to see the effects yet. He’s away with his brother on college tours. I’m anxious to dig deeper into this when he returns.


A weakness of waiting for the bend is the 10-15 minute lag time between actual blood glucose and its appearance on a CGM screen. This phenomena is like everything else in diabetes, a YDMV (your diabetes may vary) thing. Caleb may need little to no pre-bolus time but watching the CGM on a day off from school might reveal some further customizations in pre-bolus times.

My pre-bolus time later in the day is 30 minutes. I have noticed that if my blood sugar is steady at < 100 (5.6), I need to watch closely and be ready to eat earlier than my typical pre-bolus time indicates.


“First, I chose to eat a meal that I eat occasionally: a double meat and cheese hamburger with a side order of onion rings and unsweet iced tea. Total carb load (per the restaurant’s website) is 94 grams (62 for the sandwich and 32 for the O-rings). In classic Sugar Surfing fashion, I take my mealtime dose and “wait for the bend”…or at least 15-20 minutes. This was also how long it took my meal to get prepared and served to me in the store.” Quoting Ponder. I attended a workshop last year…i even got a headache.