Changes in altitude cause unintended insulin delivery from insulin pumps: mechanisms and implications.

OBJECTIVE: Children and adults with type 1 diabetes who receive insulin pump therapy have reported hypoglycemia during air travel. We studied the effects of atmospheric pressure on insulin pump delivery.

RESEARCH DESIGN AND METHODS: Ten insulin pumps were connected to capillary tubes. The effects of changes in ambient pressure on insulin delivery, bubble formation, bubble size, and cartridge plunger movement were analyzed.

RESULTS: During a flight (200 mmHg pressure decrease), excess insulin delivery of 0.623% of the cartridge volume occurred (P < 0.001, Student t test). In hypobaric chamber studies, bubbles developed in the insulin when the pressure decreased and displaced the insulin out of the cartridge. Pre-existing bubbles changed in size consistent with Boyle law. Cartridge plunger movement did not occur in normal flight conditions but did occur when catastrophic plane depressurization was mimicked.

CONCLUSIONS: Atmospheric pressure reduction causes predictable, unintended insulin delivery in pumps by bubble formation and expansion of existing bubbles.