Closing the Loop on an Artificial Pancreas

Life as a parent is never easy, but when you’ve got a kid with Type 1 diabetes it’s a little harder. Sometimes it feels like a full-time job in itself; there’s never a break. With carb counts and insulin ratios that change throughout the day, every meal is a medical procedure. A romp in the snow or a long bike ride can send her blood glucose plummeting. The overnights are the worst, though, because you never know if you overestimated the number of carbs at dinner and gave her too much insulin. Low blood glucose is easily treated with a few sips of juice, but if it goes unnoticed in the middle of the night, it could be fatal. That’s why parents of diabetics are always a little glassy eyed — we rarely sleep.

Why is all this necessary? It’s because Type 1 diabetes (T1D) is an autoimmune disease that attacks the insulin-producing beta cells in the pancreas. Once those cells are dead, insulin is no longer produced, and without insulin the rest of the cells in the body can’t take in the glucose that they need to live. Diabetics have to inject just the right amount of insulin at just the right time to coincide with the blood glucose spike that occurs after meals. Knowing how much to give and when is why we say we have to “learn to think like a pancreas.”

Animas Ping insulin pump, partial teardown. The cylinder on the bottom is the battery, the motor and syringe compartment are on top. Source: Animas

Things are better than they used to be, for sure. Insulin pumps have been a game changer for T1Ds. An insulin pump is just a tiny syringe pump. A small motor moves the plunger on a disposable syringe filled with a few days worth of insulin. The hormone is delivered through a small catheter placed under the skin every few days — painful, but better than a needle stick with every meal and snack.  A computer keeps track of everything and provides safety against overdosing on insulin, so it’s terribly convenient, but we still need to “think like a pancreas” and calculate the amount to deliver.

Even with its shortcomings, my daughter’s pump has been a blessing, and I’ll do whatever it takes to keep her in the latest gear. Pumps generally cost about $5000 or so, and need to be replaced every three years. While I’m not looking forward to paying the bill when her current pump gives up the ghost, I am certainly keen to do a teardown on the old one. I suspect it’s dead simple in there — a tiny gear motor, some kind of limit switches, and a main board. It’ll be painful to see how little my money buys, but it’ll be cool to play around with it.

Dexcom CGM sensor assembly. The little wire is the sensor that goes under the skin, and the gray blob is the transmitter. Source: Animas

Also a tremendous boon has been her continuous glucose monitor (CGM), which has a small electrochemical glucose sensor that gets inserted into her skin and sends data back to a display unit. We get a real-time graph of her approximate blood glucose level, updated every five minutes. It’s only approximate because the sensor doesn’t reach into the blood stream – it just samples the glucose in the interstitial fluid and infers a blood glucose using its twice-daily calibrations. Even still, it usually picks up hypoglycemic events and warns us so we can treat her. But it’s not perfect, so I still sleep lightly, waiting for the alarm that may never come.

So with insulin pumps and CGM, you’d think all the parts are in place to build an artificial pancreas. All it would take is to close the loop between sensing the blood glucose and calculating the correct dose of insulin And given that both pumps and CGMs all know how to talk wirelessly, it seems like a no-brainer to close the loop. There are even pumps with CGM receivers built right into them, so you know it’s just a software change to get the two devices talking to each other. And yet, at least here in the USA, we still have to close the loop manually, so the artificial pancreas remains elusive.

The painful part of this is that closed-loop CGM-integrated pumps are available elsewhere in the world. So the blocker isn’t a technical hurdle at all, but a regulatory one. The US FDA refuses to allow manufacturers to offer closed-loop pumps here, and in a way I can see their point – a pump that’s on autopilot without someone in the loop to sign off on the dosing can potentially push too much insulin and send the patient spiraling into unconsciousness, seizures, and eventually death if left untreated.

So the FDA is being careful and making the manufacturers prove the pumps are safe, and I appreciate that. But we’ve been told for years that the artificial pancreas is just around the corner, but it never seems to get here. Some people are sick of waiting, though, and have taken matters into their own hands with an artificial pancreas Android app. The project looks impressively well designed and executed, and the code is open and available for inspection. There’s no way the device would ever come close to passing regulatory muster, of course, but the fact that hackers have built a working artificial pancreas only serves to demonstrate that all the technology is here and ready to go.

For our part, we’re going to wait for a device that’s gone through testing and approval and not try to hack a stop-gap solution. At this point, I can only hope that a closed-loop system is available by the time she needs a new pump, and plan on continuing to sleep with one ear open.

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