The Hybrid Closed-Loop System: Evolution and Practical Applications

This paper validates some of my experiences using this insulin pump over the last 16 months.

Achievement of well-controlled blood glucose is essential for preventing complications in patients with type 1 diabetes. Since the inception of continuous subcutaneous insulin infusion, the aim has been to develop an artificial pancreas, with the ability to use an automated algorithm to deliver one or more hormones in response to blood glucose with the intent to keep blood sugar as close to a prespecified target as possible. Development and rapid improvement of continuous glucose sensor technology has recently allowed swift progress toward a fully closed-loop insulin delivery system. In 2017, Medtronic began marketing the 670G insulin pump with Guardian 3 sensor. When in auto mode, this is a hybrid closed-loop insulin delivery system that automatically adjusts basal insulin delivery every 5?min based on sensor glucose to maintain blood glucose levels as close to a specific target as possible. Patients receive prandial insulin by entering carbohydrate amount into the bolus calculator. Early studies show improvement in HbA1c in both adults and adolescents with this technology. Initial safety trials showed no occurrence of diabetic ketoacidosis or hypoglycemia. The utility of this device is limited by blood glucose targets of 120 and 150?mg/dL that are unacceptably high for some patients. Notwithstanding recent advances, we are far from a system that is able to replicate islet function in the form of a fully automated, multihormonal blood glucose control device.The Hybrid Closed-Loop System

Disabling Auto-Mode on my Medtronic 670G

The @Medtronic 670G auto-mode is completely useless to me. My endo and the diabetes educator recommended turning it off. That's what I'm doing. I have to live 3 more years with this POS.

I currently use the 670G with the Guardian 3 CGM. Last year my endocrinologist recommended I try the 670G and I had no issues getting approval, and I started using the system in March of 2018. My A1C is worse than it has ever been. The 670G target BG is programmed to for 120mg/dL and unchangeable. My target BG has always been 90mg/dL.

But I've had too many issues with failed sensors over the last year. I have called into the support line over two dozen times since getting the 607G. I was losing my patience, and each call into the support center ended with a " ... we will send you a replacement sensor". The support reps responses made it seem that the problem was me, not the product.

No matter how carefully I insert and tape down a sensor, The sensor reading becomes unstable when I exercise. Medtronic reps told me directly, “The sensor can become unstable during vigorous exercise.” It was recommended that when this happens, I should replace the sensor. I exercise every day. What am I supposed to do?

Eventually, after numerous calls over two months last fall, I was given a link to request a new transmitter with updated firmware. That was several weeks ago, and I have not heard anything from Medtronic.

I don’t care anymore. The system is unusable to me. If I can’t exercise safely or go hiking with a CGMS, then it serves no purpose.

This week I had a long chat with my endocrinologist. She stated her other patients were doing well on the 67G and G3. They had improved outcomes, but these are patients who were never as tightly controlled as I was. She called Medtronic on my behalf. A Medtronic diabetes educator called me, and we spoke. She admitted that my A1C would be higher with the 670G system in auto-mode and recommended disabling auto-mode. So that is what I will do.

I may talk to my endo about going back to Dexcom. The G6 seems like a fantastic bit of kit.