Effect of hypobaric air, oxygen, heliox (50:50), or heliox (80:20) breathing on air bubbles in adipose tissue.

The fate of bubbles formed in tissues during decompression to altitude after diving or due to accidental loss of cabin pressure during flight has only been indirectly inferred from theoretical modeling and clinical observations with noninvasive bubble-measuring techniques of intravascular bubbles. In this report we visually followed the in vivo resolution of micro-air bubbles injected into adipose tissue of anesthetized rats decompressed from 101.3 kPa to and held at 71 kPa corresponding to approximately 2.750 m above sea level, while the rats breathed air, oxygen, heliox (50:50), or heliox (80:20). During air breathing, bubbles initially grew for 30-80 min, after which they remained stable or began to shrink slowly. Oxygen breathing caused an initial growth of all bubbles for 15-85 min, after which they shrank until they disappeared from view. Bubble growth was significantly greater during breathing of oxygen compared with air and heliox breathing mixtures. During heliox (50:50) breathing, bubbles initially grew for 5-30 min, from which point they shrank until they disappeared from view. After a shift to heliox (80:20) breathing, some bubbles grew slightly for 20-30 min, then shrank until they disappeared from view. Bubble disappearance was significantly faster during breathing of oxygen and heliox mixtures compared with air. In conclusion, the present results show that oxygen breathing at 71 kPa promotes bubble growth in lipid tissue, and it is possible that breathing of heliox may be beneficial in treating decompression sickness during flight.