[abstract] IN VITRO MEASUREMENTS TO VALIDATE MATHEMATICAL SIMULATIONS OF BUBBLES WHICH CONTAIN MORE THAN ONE GAS

Abstract

BACKGROUND: Simulations of microbubbles using mathematical models have provided helpful insights into the behavior of decompression sickness bubbles. Controlled data for validation of the mathematical models are rare, especially when multiple gases are involved. METHODS: With videomicroscopy, we measured radius of microbubbles (originally pure oxygen and between 10 and 20 micro m radius) as they were absorbed into saline that was pre-equilibrated with 100percent O2 or with 20, 40 or 60percent O2 in N2. RESULTS: Bubble surface area decreased almost linearly with time. Disappearance time depended on original size, but area-vs-time slopes did not. Absorption rate was fastest with 100percent O2, but the rates were the same with the three mixtures: disappearance took 17 sec for a 12 micro m radius bubble. Our multiple-gas bubble model (Respir Physiol 1994; 195:131-145) predicts that N2 from the saline diffuses in rapidly and O2 diffuses out; bubbles come to a state of constant composition within 2 sec. Thereafter, pressure due to surface tension provides the only driving force for absorption and exit of N2 governs the rate. Our model matched and explained the patterns of absorption qualitatively. There is some random experimental error in the data and there is a systematic error, which we have not yet explained, whereby simulations predict disappearance about 30percent sooner than observed. CONCLUSION: a) Agreement between data and theory indicates that the computer model is valid. b) If there is no driving force except pressure due to surface tension in an aqueous environment which contains N2, free microbubbles below 20 micro m in radius last less than a minute unless they are stabilized in some way.