We are currently in the midst of a technological revolution in Type 1 diabetes management, commonly referred to as “hybrid closed-loop systems (HCL).” These systems are akin to “assisted driving” in smart cars. Each system takes an insulin pump and glucose monitor, mixes in some technological wizardry (i.e., a smart algorithm), and creates an insulin delivery system that works better with less human effort and input. It is important to emphasize, however, that these systems are NOT an artificial pancreas, nor are they a cure for Type 1 diabetes. Understanding what these systems can and (more importantly) CAN’T do, will help you to decide whether a closed-loop system is right for you, your diabetes management, and how to get the most out of one.


Basics of the Closed Loop


A hybrid closed-loop system is made up of three parts:


  • An insulin pump,
  • A continuous glucose monitor (CGM), and
  • A computer program (called an “algorithm”) that takes data from the CGM and adjusts the pump’s insulin delivery automatically.


The algorithm is the exciting and relative new kid on the block. It can raise and lower the insulin pump’s insulin delivery (within pre-set targets and limits), in an attempt to keep glucose levels within a desirable, safe range most of the time, based on readings it receives from a CGM. All commercially available closed-loop systems (Medtronic’s MiniMed 670G and Tandem’s Control-IQ with Dexcom G6) and do-it-yourself systems (Loop and OpenAPS) self-adjust the pump’s basal delivery. Some (Tandem and Loop) can also self-administer conservative bolus doses to correct glucose levels.


Automatic adjustments to insulin delivery are useful for several reasons. Basal requirements tend to vary throughout the day and can change from day to day based on an almost unlimited number of variables. Additionally, bolus doses, which remain the responsibility of the user, are sometimes miscalculated. When mealtime insulin doses come up a bit short or are too aggressive, the loop system adjusts the insulin delivery to compensate for any miscalculations. This, in turn, can help correct a glucose spike, or smooth out or minimize the extent of a glucose drop. Similar to the assisted driving features in cars, this feature protects us from potential accidents in case we lose focus momentarily.


Pros of Closing the Loop


Closed loop systems have mental and emotional benefits.  The HCL system makes small adjustments on its own, approximately every 5 minutes, based on individual data. Data includes glucose levels, movement, trends and active insulin on board. Therefore, there is less need for the user to constantly micromanage and manually adjust or override dosing and amounts of insulin delivery to maintain stable blood sugar levels. This can alleviate a significant amount of mental burden on the user and their caregivers.


Moreover, there is also less worry about low blood sugar, particularly overnight. If settings are accurate, glucose levels will remain in a safe target range for several hours without human input,.Yeah, sleep! There is also a significant reduction in stress caused by dramatic blood sugar swings. Much of the mental energy and time that is used to go into glucose management can now be used for other more enjoyable things.


Cons of Closing the Loop


It is important to keep in mind, as with any algorithm or computer program, it is only as good as the data and information it receives. In order for a HCL system to work optimally, system settings, dosing strategies, and targets need to be accurate. Also, insulin needs often change for a myriad of reasons. Users should remain patient, fluid, and open to adjustments. As with all successful management, there is a large degree of flexibility and up-keep to consider in order to obtain optimal results.


Each HCL system has its own set of advantages and drawbacks. Users need to research each system separately and speak with their provider about which options may be optimal.