Glucose Levels at the Site of Subcutaneous Insulin Administration and Their Relationship to Plasma Levels

Abstract

OBJECTIVETo examine insulin's effect on the tissue glucose concentration at the site of subcutaneous insulin administration.RESEARCH DESIGN AND METHODSA CMA-60 microdialysis (MD) catheter and a 24-gauge microperfusion (MP) catheter were inserted into the subcutaneous adipose tissue of fasting, healthy subjects (n = 5). Both catheters were perfused with regular human insulin (100 units/ml) over a 6-h period and used for glucose sampling and simultaneous administration of insulin at sequential rates of 0.33, 0.66, and 1.00 units/h (each rate was used for 2 h). Before and after the insulin delivery period, both catheters were perfused with an insulin-free solution (5% mannitol) for 2 h and used for glucose sampling only. Blood plasma glucose was clamped at euglycemic levels during insulin delivery.RESULTSStart of insulin delivery with MD and MP catheters resulted in a decline of the tissue glucose concentration and the tissue-to-plasma glucose ratio (TPR) for ∼60 min (P < 0.05). However, during the rest of the 6-h period of variable insulin delivery, tissue glucose concentration paralleled the plasma glucose concentration, and the TPR for MD and MP catheters remained unchanged at 83.2 ± 3.1 and 77.1 ± 4.8%, respectively. After subsequent switch to insulin-free perfusate, tissue glucose concentration and TPR increased slowly and reattained preinsulin delivery levels by the end of the experiments.CONCLUSIONSThe results show the attainment of a stable TPR value at the site of insulin administration, thus indicating that insulin delivery and glucose sensing may be performed simultaneously at the same adipose tissue site.

Feasibility of Adjacent Insulin Infusion and Continuous Glucose Monitoring via the Medtronic Combo-Set

“…Exploratory animal studies by members of our research group suggested significant technological barriers associated with a single line combining insulin delivery and glucose-sensing functions (Sumona Adhya personal communication). In contrast, Lindpointner and coauthors, 8,9 utilizing a single concentric microperfusion/microdialysis catheter inserted subcutaneously, have published data describing the potential viability of this approach. Interstitial fluid (ISF) glucose levels, though lower in insulin-exposed tissues, displayed a variance that was proportional and colinear with reference plasma glucose levels.…”

“…Lindpointner and coauthors 8,9 have described a concentric microperfusion and microdialysis catheter combining insulin delivery and glucose measurement. However, other studies in dogs of a combination device incorporating a glucoseoxidase-based glucose sensing electrode into the wall of an insulin infusion catheter revealed interference with the sensor during both insulin and diluent (placebo) infusion (Sumona Adhya personal communication).…”

What Are the Next Steps in Continuous Glucose Monitoring?

“…It has been shown that this approach is feasible in principle; [6][7][8] however, no product is on the market yet. Nevertheless a number of companies and researchers are working on such systems.…”

AP@home

“…One possibility to improve the acceptance of an AP system is to reduce the number of skin perforations to 1 ("single port"); this requires combing the glucose sensing with the insulin delivery. [24][25][26] Such an approach can be assumed to improve patient comfort. Therefore, for a number of years such "single port" systems are under development, mainly in Europe.…”