Insulin pumps and drop in pressure

: Do insulin pumps deliver more insulin at lower environmental pressures and, if so, is this due to pump dysfunction or to formation of bubbles in the insulin solutions? H-TRON V-100 (Hoechst Infusor V-100), MRS-1 (Disetronic), Nordic Infusor MK II (Novo Nordisk) and Minimed 504-S (Minimed Technology) insulin pumps were studied at 0.9 ATA and 0.8 ATA with constant infusion 2.0 I.U./hour. H-TRON V-100 was also studied at 0.7 ATA at the same infusion rate and with the motor in stop position. The results indicated that all pumps delivered slightly more insulin than the set rate during decompression (max. single value 2.68 I.U. extra delivered at 0.7 ATA, max. average value 1.32 I.U. extra delivered at 0.8 ATA). An equivalent amount of insulin (1.72 I.U.) was delivered at 0.7 ATA without running the motor. This implies that the extra insulin supplied was caused by physically dissolved nitrogen and oxygen in the insulin solution, and was not due to dysfunction of the pumps.