Treatment of micro air bubbles in rat adipose tissue at 25 kPa altitude exposures with perfluorocarbon emulsions and nitric oxide
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Perfluorocarbon emulsions (PFC) and nitric oxide (NO) releasing agents have on experimental basis demonstrated therapeutic properties in treating and preventing the formation of venous gas embolism as well as increased survival rate during decompression sickness from diving. The effect is ascribed to an increased solubility and transport capacity of respiratory gases in the PFC emulsion and possibly enhanced nitrogen washout through NO-increased blood flow rate and/or the removal of endothelial micro bubble nuclei precursors. Previous reports have shown that metabolic gases (i.e., oxygen in particular) and water vapor contribute to bubble growth and stabilization during altitude exposures. Accordingly, we hypothesize that the administration of PFC and NO donors upon hypobaric pressure exposures either (1) enhance the bubble disappearance rate through faster desaturation of nitrogen, or in contrast (2) promote bubble growth and stabilization through an increased oxygen supply.
In anesthetized rats, micro air bubbles (containing 79 % nitrogen) of 4–500 nl were injected into exposed abdominal adipose tissue. Rats were decompressed in 36 min to 25 kPa (~10,376 m above sea level) and bubbles studied for 210 min during continued oxygen breathing (FIO2 = 1). Rats were administered PFC, NO, or combined PFC and NO.
In all groups, most bubbles grew transiently, followed by a stabilization phase. There were no differences in the overall bubble growth or decay between groups or when compared with previous data during oxygen breathing alone at 25 kPa.
During extreme altitude exposures, the contribution of metabolic gases to bubble growth compromises the therapeutic effects of PFC and NO, but PFC and NO do not induce additional bubble growth.
KeywordsDecompression sickness Aviation Space Altitude Pilot Astronaut
The support given from Alliance Pharmaceutical Corp., San Diego, CA, for supplying the perflurocarbon emulsion—Oxygent®—is greatly appreciated. This project would have been impossible without it. The assistance of laboratory technician Mr. Ian Godfrey for his help in the manufacture of the glass micropipettes is greatly appreciated. Thanks are given to senior Hyperbaric Supervisor Michael Bering Sifakis in assisting us with chamber support and maintenance. The Lundbeck Foundation and the Laerdal Foundation for Acute Medicine supported the present work.
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