Hovorka used two devices, both commercially available. The first, a continuous glucose monitor, consists of a subcutaneous sensor that measures glucose levels in tissue beneath the skin and a device that communicates wirelessly with the sensor to download its data. The second is the pump itself, a pager-size device with an insulin reservoir that delivers the drug through a thin tube to a subcutaneous needle. Hovorka and his collaborators added an algorithm that not only put the pump and sensor in communication with each other, but also took the (sleeping) user out of the picture by determining precisely how much insulin to mete out every 15 minutes.
When tested in 12 children with type 1 diabetes, the closed-loop system brought the kids’ blood-glucose levels into the target range 61 percent of the time, up from 23 percent for those who followed their normal routine. “With the closed loop, we are able to avoid the extremes–the extreme bad low and the extreme bad high,” Hovorka says. He’s currently working with device makers in the industry to create a marketable commercial product.
Technologically, the remaining obstacles for researchers are those of refinement–for example, constructing algorithms that are exquisitely honed to predict in which direction glucose levels are moving and at what rate. Other researchers are working on sensors that can monitor blood glucose over an extended period of time (currently, sensors must be replaced every three to eight days) and with improved accuracy.
Despite the fact that much of the technology is on the market, researchers must still prove to the FDA that their system is safe when combined with the algorithms, and that if anything goes wrong–if a sensor goes wonky or the insulin pump clogs up–the computer can sense it and either set off an alarm or turn the whole system off.
“You don’t have to get the perfect system to make a tremendous advance and make it considerably easier to live with diabetes,” says William Tamborlane, chief of pediatric endocrinology at Yale School of Medicine, who invented insulin-pump therapy in the late 1970s. As a clinician, he’s more interested in seeing these incremental advances make their way to the patients than in waiting for a perfect system to be created. “We now have sensors that can say what the blood sugar’s doing every minute,” Tamborlane says. “And we have insulin pumps that can change how much insulin it gives on a minute-to-minute basis. We have the technology right now to come pretty close to what might be considered the ultimate solution.”