Understanding your options and how they compare can help you decide which hybrid closed loop system would best meet your needs. Not your doctor’s. Not your health insurance’s. YOURS.
There are several HCL systems available: some that have been approved by government authorities and are produced/marketed by major diabetes device companies, and others that are classified as “DIY” (Do It Yourself) – systems that the user builds on their own using commercially-available components. Down the road, this will likely change radically as “interoperability” comes to the forefront. With interoperability, users may select a pump, CGM and algorithm from different manufacturers and have them work together seamlessly. Until then, the systems are mostly integrated by manufacturer.
Hybrid Closed Loop Systems Options
The current commercially available systems include the Medtronic 670G and Tandem X2 with Control IQ.
Medtronic was the first company to launch an HCL back in 2018. It features the Medtronic 670 tubed insulin pump and the Medtronic Guardian 3 sensor. The sensor lasts for seven days and requires a minimum of two fingerstick calibrations daily. It uses a rechargeable transmitter which communicates with the pump using radio signals. Within the pump is an algorithm called “auto mode” that adjusts the pump’s basal insulin delivery every five minutes based on the sensor readings. The algorithm starts with a flat 24-hour basal program (based on the user’s total daily insulin requirements) and adjusts the basal rate from there. There are set limits to how much (and for how long) the algorithm will raise or lower the basal delivery. The system uses a preset target of 120 mg/dl when adjusting basal delivery and a target of 150 mg/dl when calculating correction boluses. A temporary basal adjustment target of 150 mg/dl can be set prior to exercise.
Tandem’s Control IQ system features the sleek Tandem t:slim tubed insulin pump with a full-color touch-screen.
CGM data reaches the pump via Bluetooth signals from the Dexcom G6 sensor, which lasts 10 days and requires no calibrations. Activating the Control IQ algorithm requires the mere flip of a switch and entry of the user’s weight and average daily insulin requirements. The algorithm predicts where the glucose will be in 30 minutes (based on CGM values and trends) and adjusts the pump’s usual basal delivery based on the predicted value.
The system can also administer conservative correction boluses on an hourly basis if the glucose is predicted to be quite high or remains high. It has a preset target of 110 mg/dl. Extended boluses (but not temporary basal rates) remain an option when Control IQ is running. The system has two optional “activity” overrides: An exercise setting (which makes the algorithm more conservative) and a sleep setting (which makes the algorithm slightly more aggressive but turns off automated correction boluses).
The current “build-it-yourself” systems include the Loop app, OpenAPS and AndroidAPS
All three consist of a combination of FDA-approved products (the pump and CGM) and a non-approved app which serves as the controller/algorithm. The apps were designed and built by people in the diabetes community who were looking for a better system than those that are commercially available. The apps themselves are free; they can be built by following a series of instructions that are available online. However, they do require the builder to have a software developer license (specific to Loop and available to anyone for a modest annual fee) and some ancillary parts for allowing proper data transmission between devices (once again, for a modest fee). Because the Loop app sits on the user’s phone, most pump programming (including bolus calculations and programming) can be done right on the phone.
Loop can interact with older-model Medtronic Paradigm tubed insulin pumps (firmware 2.4 or lower) and previous-generation (Eros) OmniPods – both of which transmit and receive radio signals. It can receive data from the Dexcom G5 or G6 CGM. The app can be built on an Apple computer and runs on an iPhone or iPod Touch. It requires the use of a small signal converter called a “RileyLink” which can be ordered online for approximately $150. Loop applies the user’s customary basal rates as a starting point, and adjusts basal delivery based projected glucose values (from sensor data), active insulin, and active carbs. It allows the user to choose a maximum allowable basal level as well as the degree of adjustment whenever predicted and actual glucose levels vary. It applies the user’s preferred carb ratios, correction factors, targets, and insulin-on-board algorithms. Although extended and combination (square/dual) boluses are not available, Loop offers the option of entering the “absorption time” for any carb entry. With a longer absorption time, less bolus will be delivered up-front, and the basal delivery will be increased over the next several hours. Finally, Loop allows the user to set a variety of “temporary overrides” which essentially make the algorithm more or less aggressive for a chosen period of time. Details about the Loop app can be found at https://loopkit.github.io/loopdocs/
OpenAPS and AndroidAPS are similar to Loop
They can work with older-model Medtronic pumps, and AndroidAPS works with some select older Medtronic pumps and the Accu-Chek Combo and Dana pumps. They are compatible with a variety of CGM systems, including Dexcom G4, G5 and G6, as well as the Medtronic Guardian and Freesytle Libre. OpenAPS runs on both iPhone and Android devices. AndroidAPS runs on Google Android phones. For OpenAPS, communication between the app, CGM and pump requires ongoing web access. This means carrying a small computer circuit board and portable battery. Building the app takes a lot more “coding” and tech know-how than Loop, so it is used mainly by those who are wed to an Android device. Details about OpenAPS can be found at https://openaps.org/. AndroidAPS uses OpenAPS code, but is unique in that it doesn’t require the small computer circuit board to work. Details about AndroidAPS can be found at https://androidaps.readthedocs.io/en/latest/EN/
Hybrid Closed Loop Systems Comparisons
Which Hybrid Closed Loop will take home the award for best supporting system?
At last, the moment we’ve all been waiting for. Which HCL will take home the award for best supporting system? As with a movie, beauty is in the eye of the beholder. Different features are simply more important to different people. Personally, I couldn’t care less about whether or not the government deems my system to be safe. All that matters to me is that it works. Others consider simplicity and convenience to be essential, or customization to have the utmost importance. Out-of-pocket costs play a major role for some.
First, some general observations. Compared to commercially available systems, DIY systems allow much greater flexibility in terms of setting personal parameters. The software can be updated frequently as new strategies and products become available. For example, within weeks of Novo Nordisk’s Fiasp insulin hitting the market, Loop designers installed and algorithm for calculating insulin-on-board based on a Fiasp action curve. Because the DIY apps are interoperable, users have multiple pumps and CGM systems from which to choose. And because the algorithms can be set to the user’s desired intensity level, the outcomes consistently outperform those of the commercial systems.
Of course, there are drawbacks to using a DIY system. They often require the use of older-model insulin pumps. There is no manual, warranty or customer support offered with the app – just an online community of peers to assist with troubleshooting. Users must carry extra equipment to allow the app to communicate with the pump, and the equipment usually requires daily charging. Most healthcare providers have limited experience with DIY systems, and hence cannot offer much in the way of guidance. Some will actually decline to care for patients who choose to use a “non-approved” system. There are limited options for accessing data and generating reports from DIY systems: Tidepool is one option, along with Nightscout. Unfortunately, neither of these integrate easily into the medical records systems at most diabetes clinics.
But perhaps the most significant obstacle to use of a DIY system is the fact that the user needs to “build” the app on their own. Building an app can be a long and arduous process, especially for those with limited computer tech skills. It also requires specific types of operating systems on both the computer and the smartphone.
So here are our ratings (along with some explanation, where appropriate) on the factors of: Safety (minimizing hypoglycemia and system errors), Performance (degree of glucose control that can be achieved), Simplicity (ease of initial setup and daily use), Convenience (effort/disruption incurred by the user on a daily basis) and Cost (for hardware and disposables), for each HCL system.