Automated insulin delivery systems are automated (or semi-automated) systems designed to assist people with insulin-requiring diabetes, by automatically adjusting insulin delivery in response to blood glucose levels. Currently available systems (as of October 2020) can only deliver (and regulate delivery of) a single hormone—insulin. Other systems currently in development aim to improve on current systems by adding one or more additional hormones that can be delivered as needed, providing something closer to the endocrine functionality of the pancreas.
The endocrine functionality of the pancreas is provided by islet cells which produce the hormones insulin and glucagon. Artificial pancreatic technology mimics the secretion of these hormones into the bloodstream in response to the body's changing blood glucose levels. Maintaining balanced blood sugar levels is crucial to the function of the brain, liver, and kidneys. Therefore, for people with diabetes, it is necessary that the levels be kept balanced when the body cannot produce insulin itself.
Automated insulin delivery (AID) systems are often referred to using the term artificial pancreas, but the term has no precise, universally accepted definition. For uses other than automated insulin delivery, see Artificial pancreas (disambiguation).
General overview
History
The first automated insulin delivery system was known as the Biostator.
Classes of AID systems
Currently available AID systems fall into three broad classes based on their capabilities. The first systems released can only halt insulin delivery (predictive low glucose suspend) in response to already low or predicted low glucose. Hybrid Closed Loop systems can modulate delivery both up and down, although users still initiate insulin doses (boluses) for meals and typically "announce" or enter meal information. Fully Closed Loops require no manual insulin delivery actions or announcement for meals.
Predictive Low Glucose Suspend (PLGS)
A step forward from threshold suspend systems, predictive low glucose suspend (PLGS) systems use a mathematical model to extrapolate predicted future blood sugar levels based on recent past readings from a CGM. This allows the system to reduce or halt insulin delivery prior to a predicted hypoglycemic event.
Hybrid Closed Loop (HCL) / Advanced Hybrid Closed Loop (AHCL)
Hybrid closed loop (HCL) systems further expand on the capabilities of PLGS systems by adjusting basal insulin delivery rates both up and down in response to values from a continuous glucose monitor. Through this modulation of basal insulin, the system is able to reduce the magnitude and duration both hyperglycemic and hypoglycemic events. Users still must initiate manual mealtime boluses. Advanced hybrid closed loop systems have advanced algorithms.
Fully Closed Loop (FCL)
Fully or full closed loop (FCL) systems adjust insulin delivery in response to changes in glucose levels without requiring input by users for mealtime insulin or announcements of meals.
Required components
An automated insulin delivery system consists of three distinct components: a continuous glucose monitor to determine blood sugar levels, a pump to deliver insulin, and an algorithm that uses the data from the CGM and pump to determine needed insulin adjustments.
In the United States, the Food and Drug Administration (FDA) allows each component to be approved independently, allowing for more rapid approvals and incremental innovation. Each component is discussed in greater detail below.
Continuous glucose monitor (CGM)
Continuous glucose monitors (CGMs) are wearable sensors which extrapolate an estimate of the glucose concentration in a patient's blood based on the level of glucose present in the subcutaneous interstitial fluid. A thin, biocompatible sensor wire coated with a glucose-reactive enzyme is inserted into the skin, allowing the system to read the voltage generated, and based on it, estimate blood glucose. The biggest advantage of a CGM over a traditional fingerstick blood glucose meter is that the CGM can take a new reading as often as every 60 seconds (although most only take a reading every 5 minutes), allowing for a sampling frequency that is able to provide not just a current blood sugar level, but a record of past measurements; allowing computer systems to project past short-term trends into the future, showing patients where their blood sugar levels are likely headed.