The glucose sensor: the missing link in diabetes therapy.

This review considers the present state of the implantable glucose sensor from the point of view of technical models available today. Chemical analysis behind the practical experiences under both in vitro and in vivo conditions are described (Abel, Fischer, Brunstein and Ertle 1988; Bruckel, Kerner, Zier, Steinbach and Pfeiffer 1988a; Bruckel, Kerner, Zier, Steinbach and Pfeiffer 1988b; Steinbach, Kerner, Zier, Dolderer and Pfeiffer 1987). Amperometric enzymatic glucose sensors are used by the majority of laboratories, providing satisfactory results of glucose determinan in solution and in the laboratory. Up to 4 days of reliable values were recorded by measuring glucose in vivo, in practical terms, in the subcutaneous tissue in animals. However, also in this first period of foreign-body reactions, enough encapsulation obviously occurs to neutralize the majority of the sensors implanted. In first experiments in humans, the results are even worse. Generally, decreasing activity was observed in less than 24 h. Therefore, continuous blood glucose monitoring by portable glucose sensors used the same principle in a flow-through chamber; the sensor of our own make was employed in a number of clinical conditions. When one of the available insulin pumps effecting continuous subcutaneous insulin infusions was connected, the algorithms worked out for the big AEP under bedside conditions were also of use in a slightly modified fashion for the subcutaneous insulin application. Renouncing the computer-mediated automated regulation of the insulin delivery is possible when the patient is constantly reading his blood glucose values and operates the insulin infusion pulses in association with meals. Continuous glucose monitoring by portable instruments is the only and irreplaceable prerequisite for unprejudiced evaluation of the various strategies for substitution of the insulin deficiency in any form of diabetes.