Glucose concentration at possible sensor tissue implant sites.

It is generally acknowledged that the ideal automatic insulin infusion system would be a closed loop that metered insulin delivery in response to a feedback sensor such as an implantable glucose detector. Most current efforts are aimed at a transducer located within the blood vascular tree. We believe that the blood constitutes an especially hostile environment for such a device. The possibility of placing the sensor with a reasonably rapid response to dynamic alterations in glucose metabolism in a space containing fluid outside the bloodstream was studied. The subcutaneous extracellular space, peritoneum, pleura, and pericardium were included. Generally, the concentration of glucose ranged between 50 and 115 mg/dl under steady-state conditions. The experimental design did not permit monitoring rapid responses to artificially induced dynamic changes. There were several situations where lower values were recorded, suggesting that a wide range of concentrations might occur. The authors have concluded that these experimental results are compatible with the possibility of a suitable locus for the glucose sensor in the extracellular, extravascular space.