Two days on a closed loop system

A few weeks ago, I completed a closed loop clinical trial at Montefiore Medical Center in the Bronx. During two visits, all my insulin dosages were calculated and delivered automatically by a Medtronic system analyzing my blood sugar data. It was the first times since being diagnosed in 1986 that I didn’t have to carb count or make any other decisions about my medication levels. As exciting and encouraging as that was, the whole experience tempered my hope that this approach will replace my current treatment any time soon.

Medtronic’s visualization of their algorithm and insulin activity.

I spent my first night in the hospital in August and returned a few weeks later in September. Each visit began in the afternoon and ran through the following evening.

The trial was run by Dr. Heptulla, the Division Chief of Pediatric Endocrinology at Montefiore. Dr. Heptulla is know for her strong interest in using technology to treat diabetes. This is one of the many clinical studies she has completed, with several more in the works.

Both times, I used Novolog insulin. On the second visit I was also given a shot of Victoza, a drug normally used only on type-2 diabetics. It slows down digestion and helps reduce post-meal blood sugar spikes. The trial’s main goal was to test whether the drug could be helpful in combination with a closed loop system to better control blood sugar levels.

The study used a Medtronic insulin pump and 3 Medtronic CGMs (continuous glucose monitors). Two of the sensors were the new Medtronic Enlite (just approved by the FDA a few weeks ago) and one older model Sof-Sensor. The data was all transmitted wirelessly to a Medtronic Comlink receiver and into a PC running Medtronic’s analysis algorithm.

The pump in the study was the same generation as my current one. The Medtronic CGM transmitters haven’t changed, even though there is a new generation of sensor.

The new Enlite CGM sensors

Medtronic Comlink wireless receiver

Mission control

The pump delivered micro-boluses of insulin (usually 0.1u) when the system sensed rising blood sugars. All other basal rates were turned off. The CGMs, which usually take readings every 5 minutes, were instead generating blood sugar readings every minute. Nurses also drew blood every half hour for 28 hours for a more accurate glucose test in plasma. The first night I learned to lay in bed with my arm extended and the IV exposed, allowing me to successfully sleep through a few overnight blood draws.

0.1u microboluses every few minutes

Medtronic software screenshot. It shows readings from the 3 CGMs, the regular blood tests taken every half hour and the microbolus dosages of insulin.

During the first visit, there were big spikes in my blood sugar after every meal, peaking at about 250 mg/dL. The system then often over-corrected and my blood sugars crashed. I took glucose tablets to treat any blood sugar below 70 mg/dL.

My blood sugars for the first visit. The vertical red lines mark my meals.

Before my second visit, I had been warned that the side effects of Victoza include nausea and headaches. But most previous participants in the study hadn’t experienced any major problems (except one patient who did get sick). I was given the shot before the 8pm dinner the first night. I still had a big spike after eating (the drug hadn’t kicked in yet). Around midnight, my blood sugars went really low. I ended up needing 48g of carbs (which meant eating 12 glucose tablets) to get back in-range (normally I need only about 15g).  But for several hours after that, my blood sugars were near perfect and I needed almost no insulin.

When I woke up however, I knew something was wrong. I was able to eat breakfast (a Boost shake) at 7am. But soon after that I became nauseous and stayed that way until about 4pm. I couldn’t eat any lunch and was only able to eat about a quarter of my dinner. So much for giving the study usable data on how well the Victoza works on meals. But I’m sure there’s value in knowing how many patients can’t tolerate the drug in the first place.


Given how I felt, I wasn’t able to keep track of my blood sugars for the second visit and can’t share them here. But I remained pretty steady most of the second day in part because I wasn’t eating.

Despite my reaction to the Victoza, I’m glad I participated in this study. It’s interesting to experience first-hand the potential of this technology. The biggest problem was the post-meal high blood sugars. It seems like the cause is the double lag in both data and insulin.  The CGM readings are 20 minutes behind current blood sugar levels because it tests outside the blood stream. When insulin is factored in, which takes 20 minutes to start working and an hour to peak, the system is always operating behind the curve.

A hybrid approach that includes pre-meal dosing seems like the most promising alternative to a pure closed loop system. This method has been integrated into some of the tests of the bionic pancreas by the Massachusetts General Hospital team. Patients use an iPhone app to enter that they are eating a small, medium or large meal. The system then delivers a percentage of a standard dosage (I think it’s around 50%) right away. The algorithm takes care of the rest of the insulin delivery and is able to reduce the severity of post-meal spikes. The bionic pancreas is also highly effective because it doses glucagon to treat low blood sugars too.

Looking back on my experience, it’s encouraging that we’re finally making real progress toward an artificial pancreas. I still have my doubts that any of these systems will hit the market within the next decade, but that’s simply my guess. Another possibility is that it will take several generations of hardware, software and medications before all the issues are resolved and patients don’t have to take any action in regulating their devices.

But until we get there, I’m still excited to be working on better self-management support systems. There’s plenty more we could be doing with existing technologies and treatments to help us stay healthy until that cure arrives.

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