Novel Methods to Understand the Temporal Nature and Accuracy of Delivery for Insulin Infusion Pumps

A wide suite of methods are available to evaluate delivery accuracy of insulin pumps. However, these methods do not capture any temporal information, which may be critical for design of artificial pancreas (AP) systems. We propose a novel video microscopy method to understand the delivery accuracy and temporal nature for a new durable pump under development (IFP), and a commercially available pump (Medtronic 722G, M722G).

The cannula tip of an infusion set is inserted into a graduated pipette placed under a digital microscope. A video of the delivery is captured to track the fluid meniscus, to measure volumetric delivery rate and accuracy. This was done for a programmed value of 0.5 and 1 U. A similar procedure was adopted to track linear motion of the piston rod, which actuates the reservoir plunger, for a programmed value of 10 U.

It was observed that the commercially available pump delivers insulin in pulses of 0.05 U every two seconds. The mean absolute volumetric delivery error (MAE) for both pumps was found to be within the values reported previously. More importantly, it was found that a significant fraction of the programmed value is delivered, after completion of the planned bolus duration (IFP: 14.31% vs M722G: 9.38% for 1 U delivery).

The methods presented in this article help understand the delivery dynamics of liquid drug delivery devices. Our results indicate that a significant fraction of insulin delivery happens after the planned bolus duration, which might be important consideration for design of AP systems.