Closure of the loop by glucose sensing. Physiological and practical considerations.

This review considers factors which determine the minimum desirable operational function of a glucose sensor, based on a consideration of the meal, basal and exercising phases of metabolism in the insulin-dependent diabetic. Augmented insulin release ahead of, or in synchrony with, the arrival of nutrients in the blood stream is important in the normal regulatory mechanism associated with meals. Thus glucose sensors are not suited to be the sole means of determining insulin delivery during meals, and this phase of metabolic control may best be handled by open-loop insulin delivery. However during other phases of metabolic control, glucose sensors with modest response times may have a very useful clinical function.