Characterizing normal-use temperature conditions of pumped insulin

Abstract

In this study, the temperature profiles of insulin pump reservoirs during normal wear conditions across multiple seasons were characterized. Thermocouples secured in reservoirs filled with insulin diluent were loaded in infusion pumps worn by volunteers. Reservoir and ambient environmental temperature data and activity levels were logged during the course of normal daily activities in February (winter), April (spring), and August (summer). Each seasonal data set comprised 7 to 14 days of wear from 3 to 5 volunteers. Reservoir temperature profiles were generally higher than ambient temperatures, likely due to heat transfer from the wearer when the pump was placed close to the body. Temperature conditions inside pump reservoirs fluctuated between 25°C and 37°C regardless of seasonal variations. The average reservoir temperature remained close to 30°C across all seasons, notably lower than used in previously published compatibility and stability protocols (37°C). Results from this study could be utilized to develop more accurate stability and compatibility testing procedures for new insulin formulations and/or delivery devices.

Keywords: continuous subcutaneous insulin infusion; insulin delivery device testing; insulin pump temperature; thermal monitoring.

Figure 1.

Real-time temperature logging configuration: (a) Omega wire thermocouple secured into an Animas 2.0 mL reservoir filled with insulin diluent. (b) Volunteer wearing pump/data logger pack on belt clip during 72-hour temperature logging study.

Figure 2.

Mean pump reservoir (red) and ambient air (blue) temperatures (±95% CI) logged for each season across all volunteers and all days.

Figure 3.

(a) Distribution for pump reservoir and ambient air temperatures across all seasons and subjects. (b) Temperature change distribution for all subjects across all seasons.