Experimental and Theoretical Studies of Pulsed Micro Flows Pertinent to Continuous Subcutaneous Insulin Infusion (CSII) Therapy

Continuous subcutaneous insulin infusion (CSII) therapy, also known as insulin pump therapy, has become an important advancement in diabetes therapy to improve the quality of life for millions of diabetes patients. Insulin delivery failures caused by the precipitations of insulin within micro-sized CSII tubing systems have been reported in recent years. It has also been conjectured that the flow of insulin through an insulin infusion set may be reduced or inhibited by air bubbles entrained into the capillary CSII tubing system during the typical three- to five-day operation between refills. Currently, most solutions to insulin occlusion related problems are based on clinical trials. In the present study, an experimental and theoretic study was conducted to investigate the pulsed flows inside the micro-sized CSII tubing system. A micro-PIV system was used to provide detailed flow velocity field measurements inside the capillary CSII tubing system to characterize the transient behavior of the micro-flows upon the pulsed actuation of the insulin pump used in CSII therapy. It was found that the microflow inside the CSII tubing system is highly unsteady, which is much more interesting than the creeping flow that the nominal averaged flow rates would suggest. A theoretic frame work was also performed to model the pulsed micro-flows driven by the insulin pump to predict the transient behavior of the microflows and velocity distributions inside the micro-sized CSII tubing system. The measurement results and the theoretic predictions were compared quantitatively to elucidate underlying physics for a better understanding of the microphysical process associated with the insulin delivery in order to provide a better guidance for troubleshooting of insulin occlusion in CSII therapy.