Single Hormone Closed Loop Study With PDT Sensor

The study described within this protocol is designed to test a single hormone closed-loop algorithm for managing blood glucose in type 1 diabetes using insulin only and a new device for measuring glucose continuously in the immediate vicinity of subcutaneous insulin delivery. Subjects will undergo one all day closed loop study using insulin only. The closed loop insulin only system includes a Dexcom G5 transmitter, a Nexus 5 smart phone and two Tandem tslim pumps connected to two Pacific Diabetes Technologies glucose sensing cannulas. The closed loop system will be started after G5 2 hour sensor start-up with an IV catheter for frequent blood withdrawal for 10 hours.

Subjects will undergo one 12 hour inpatient study. During this intervention visit, subjects will wear the single hormone closed loop system which includes two t:slim insulin pumps to deliver insulin or saline through two investigational PDT glucose sensing cannulas, and a Dexcom G5 CGM to measure glucose. The subject will come to the research center at approximately 7am for the inpatient visit. The Dexcom G5 sensor and PDT glucose sensing cannulas will be placed after arrival. An 18-22 gauge IV catheter will be placed for blood sampling every 15 minutes after sensor warm-up is complete for measuring blood glucose concentration. After a 2 hour warm-up period for the G5 sensor, glucose will be controlled using the FMPD single hormone mode. The single hormone mode of the controller determines insulin delivery rates based on proportional and derivative error through one t:slim insulin pump. The second t:slim insulin pump will deliver normal saline at the same delivery rates as the insulin. Subjects will eat breakfast and lunch at approximately 11 am and 3 pm respectively. Subjects will have the ability to complete light exercise on a treadmill. The closed loop system will be stopped at approximately 6pm with removal of all devices. During the study, the subject will wear one subcutaneous DexcomTM G5 continuous glucose monitoring (CGM) system. The CGM system will provide sensed glucose data every 5 minutes. The accuracy of the sensed data will be obtained by reference measurements of two YSI venous blood glucose values to calibrate the sensor at the beginning of the closed loop study. Sensed glucose data will be wirelessly transmitted via Bluetooth Low Energy (BTLE) from the Dexcom G5 transmitter to the Nexus 5 master controller every five minutes. The controller is a Google Nexus 5 phone. The smart phone will wirelessly communicate via BTLE to two Tandem t:slim insulin pumps, one for automated insulin delivery and one of automated saline delivery.