What is OpenAPS: Part 4

Since building my OpenAPS a month and a half ago, I have received innumerable questions about what it is and how it works by people with and without T1D. For this reason, I have written an explanation for folks who are looking to learn more or share a concise explanation with their communities. The explanation catered to T1Ds is first, followed by the explanation catered to 5.5ers (people not living with T1D). ENJOY!

What is OpenAPS?

OpenAPS (Open Artificial Pancreas System) is a closed loop system used to integrate continuous glucose monitoring (CGM) technology with insulin pump technology. The system creates temporary basal rates based on CGM data, both increasing and decreasing, according to your targets. It is able to integrate a combination of Medtronic insulin pumps, Dexcom, and the enlite sensor. This flowchart makes it pretty clear as to what technology is compatible with the resources in OpenAPS.


There are a few ways that this integration can be visualized: Nightscout, Loop, or offline. I was under the impression that the Nightscout option has been the most popular, but I don’t know enough about the Loop crew to know how popular it is.

Nightscout is a technology that was created by parents of kids living with T1D that enabled them to visualize CGM data. I’m pretty stoked that it exists now but didn’t when I was a teenager (sorry Mom and Dad)!  It essentially broadcasts CGM and pump data onto a website and has the functionality to generate reports too.

Loop is super cool, it is an app (Apple only, boooo) that is compatible with Rileylink and allows you to visualize the activity of the closed loop. You can also bolus from the app which sounds like a dream. I know the least about this one, but it appears to be the most straightforward setup and most user-friendly.

I by chance ended up in a closed loop that works offline. I use an Enlite CGM, a Medtronic pump, and Android/Windows. This eliminated Loop as an option, and I decided to go with OpenAPS with Nightscout because there are so many resources that could help me out. From here I set up my Nightscout site and the closed loop but encountered some problems visualizing my data properly.  I am lucky that my CGM can be read from my pump anyway so I can look at exactly what the loop is doing when I upload my pump data on Carelink. Sure, I don’t visualize it in real time, but I can see the temporary basals that it puts on my pump as they happen. I also don’t have to worry about always having my phone on me, data usage, or going out of cell service.

The nature of OpenAPS and its sibling rigs are to be customizable. If you are interested in creating a rig that works for your particular set up, do some digging and connect with groups that are also working away on their rigs. The community is ingenious and extremely helpful!


There are two main parts of diabetes management, testing blood-sugar levels, and giving insulin. Insulin acts as a gate-keeper for sugar to get out of the bloodstream and into cells, so giving insulin decreases blood-sugar levels and not taking insulin increases blood-sugar levels. Insulin isn’t the only variable for diabetes management though, food, exercise, stress, and several other variables affect blood-sugar levels too. The many variables that affect blood-sugar levels inconsistently mean that it is impossible for diabetes to be an exact science.

In principle, there is a simple solution, a closed loop. A device that measures blood-sugar levels continuously and automatically gives/withholds insulin from the person based on the measurement. Guess what? A continuous glucose monitor exists, and insulin can be dosed by a pump.

In practice, there are a few obstacles. First, insulin is not instantaneous. The fastest insulin on the market takes 15 minutes to act and lasts for a few hours. The common insulins that people use peak at 30 minutes and last for 4 hours. So while the continuous glucose monitor measures blood-sugar levels in real time (sort of, that part is a little complicated), insulin does not work on the same clock. This obstacle can be overcome using a small bit of mathematical modeling that predicts the ‘active insulin’ that is still working in a person hours after dosing.

Another key obstacle (in the past, and still sort of currently), has to do with the regulation of medical devices that automatically deliver insulin. In the past, it has been challenging for companies to get approval for automatic medication administration due to how variable the accuracy of continuous glucose monitors is. So commercially it has been a challenge to get the miracle device to market. This is no longer the case, as Medtronic came out with their 670G. The system, however, is pretty soft. The target range is fairly high and cannot be personalized.

Luckily, the system can be hacked into. OpenAPS is a project that has developed a system for your layperson to build and program an Intel Edison (plus computer board and lithium battery). The system integrates blood glucose and insulin information, and most importantly AUTOMATICALLY CHANGES INSULIN DOSES. The fact that the system is created by the patient is very powerful because it means that more aggressive settings than are approved for commercial products.




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