Why is Continuous Glucose Monitoring So Hard?

Everyone starts their day with a routine, and like most people these days, mine starts by checking my phone. But where most people look for the weather update, local traffic, or even check Twitter or Facebook, I use my phone to peer an inch inside my daughter’s abdomen. There, a tiny electrochemical sensor continuously samples the fluid between her cells, measuring the concentration of glucose so that we can control the amount of insulin she’s receiving through her insulin pump.

Type 1 diabetes is a nasty disease, usually sprung on the victim early in life and making every day a series of medical procedures – calculating the correct amount of insulin to use for each morsel of food consumed, dealing with the inevitable high and low blood glucose readings, and pinprick after pinprick to test the blood. Continuous glucose monitoring (CGM) has been a godsend to us and millions of diabetic families, as it gives us the freedom to let our kids be kids and go on sleepovers and have one more slice of pizza without turning it into a major project. Plus, good control of blood glucose means less chance of the dire consequences of diabetes later in life, like blindness, heart disease, and amputations. And I have to say I think it’s pretty neat that I have telemetry on my child; we like to call her our “cyborg kid.”

But for all the benefits of CGM, it’s not without its downsides. It’s wickedly expensive in terms of consumables and electronics, it requires an invasive procedure to place sensors, and even in this age of tiny electronics, it’s still comparatively bulky. It seems like we should be a lot further along with the technology than we are, but as it turns out, CGM is actually pretty hard to do, and there are some pretty solid reasons why the technology seems stuck.

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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.”

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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.

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