Normalization of glycemia in diabetics during meals with insulin and glucagon delivery by the artificial pancreas

Abstract

An extracorporeal closed-loop system was employed to maintain glycemia in the normal range during consumption of meals in 9 insulin-treated diabetics. This artificial pancreas system incorporated continuous blood glucose monitoring (0.05 ml/min, delay time 90 s), a computer programmed to respond to glycemia and a hormone delivery system. I.v. insulin delivery rates were determined by control parameters responsive to both glucose concentration and its rate of change. Because insulin-dependent diabetics often defend themselves poorly against hypoglycemia (in some cases due to inadequate glucagon responses), the instrument was also programmed for exogenous glucagon delivery. A priori selection of ideal parameters for insulin and glucagon delivery for each individual is not yet possible. Consequently, when the parameters were used for the 1st time on each subject, they were varied over a reasonable range. This approach resulted in a corresponding variety of glycemic responses, the average of which characterized a set of initial parameters that is generally applicable. Appropriate control parameters are presented that successfully prevented hypoglycemia. Glucagon delivery directly related to glycemia appeared sufficient for this purpose, obivating the need for dextrose administration. This system provides a technique for complete normalization of blood glucose concentration in the types of diabetics tested, during both fed and interprandial periods, and has yielded insights essential to the development of more sophisticated future devices.