“Our data suggest that a semi-closed loop system using the subcutaneous route for glucose measurement and insulin application is possible. Although the time delay of insulin action means that a 'feed-forward' insulin dose is necessary, during nighttime the feedback part of the algorithm is able to achieve good control,” Dr. Freckmann said.
Indeed, such time delays will always occur with sensors that monitor glucose in the interstitial fluid, according to Dr. Jeffrey I. Joseph, director of the Artificial Pancreas Center at Thomas Jefferson University, Philadelphia.
Minimed Medtronic has been developing a glucose sensor that measures changes in the oxygen concentration within the superior vena cava, where it is implanted for the long term. Using the vascular sensor and a peritoneal implantable insulin delivery device, French researchers have demonstrated the feasibility of a closed-loop system.
Although the physiological delay with this system is tiny, here the problem is longevity. From a practical standpoint, any implantable device would need to work for at least 7 years to be viable. Currently the Minimed system must be replaced every 12–16 months, Dr. Joseph noted.
Since 1996, he has been working with another major insulin pump manufacturer, Animas (www.animascorp.com
At least two other companies are forging ahead with continuous glucose sensors. Abbott's Navigator, currently under review by the Food and Drug Administration, would be used to make therapeutic decisions, although calibration by the user would still be required (www.abbottdiabetescare.comwww.dexcom.com