Background and Aims

Glycemic variability is still an issue among subjects with type 1 diabetes treated with pump. Erratic subcutaneous (SC) absorption and poor diffusion at the injection site are among the suspected causes for this phenomenon. Assessing insulin SC propagation is a challenge when it is administered by basal rate (BR) through pump and was scarcely studied. As speed of absorption increases with depot surface, we propose a descriptive method linking pump delivery and SC propagation of insulin through follow-up of catheter pressure and high-precision time-spread imaging.

Methods

Administration of insulin (Aspart®) and contrast agent was performed via a pump (t:slim x2, Tandem®) at 1UI/h BR in ex-vivo human skin explants from post-bariatric surgery. Samples were placed in a micro-CT scanner. During 3h, one 3D-image every 5min, and continuous pressure in the tubing were recorded.

Insulin depot was numerically isolated (see figure, insulin identified in green in 2D and 3D). From depot area and volume we define a unitless dispersion index (DI) which characterizes the spread of insulin. DI is computed for each 5-minutes step of the infusion.

Results

Hypodermis was reached by cannula in 14/24 injections. One injection was extradermal, others were intradermal.

Insulin spreads preferably along the interlobular septum.

DI increases with time for all tissue-reaching injections, up to a mean value of 6.99(+/- 0.73) after 3h.

Bubbles detected via imaging were matched with pressure events in the tubing.

Conclusions

At fixed conditions, DI standard deviation is low. This encourages DI use for injection parameters comparison such as pump model or BR impact.