Decompression induced bubble dynamics on ex vivo fat and muscle tissue surfaces with a new experimental set up

• A set-up was developed for the study of decompression induced bubble growth.
• The surface and absorption dynamics were decoupled.
• Heterogeneous nucleation was observed from preferential sites on the tissues.
• Differences in bubble behavior were shown for fat and muscle tissue substrates.
• A competition for dissolved gas between adjacent multiple bubbles was demonstrated.

Vascular gas bubbles are routinely observed after scuba dives using ultrasound imaging, however the precise formation mechanism and site of these bubbles are still debated and growth from decompression in vivo has not been extensively studied, due in part to imaging difficulties. An experimental set-up was developed for optical recording of bubble growth and density on tissue surface area during hyperbaric decompression. Muscle and fat tissues (rabbits, ex vivo) were covered with nitrogen saturated distilled water and decompression experiments performed, from 3 to 0 bar, at a rate of 1 bar/min. Pictures were automatically acquired every 5 s from the start of the decompression for 1 h with a resolution of 1.75 μm. A custom MatLab analysis code implementing a circular Hough transform was written and shown to be able to track bubble growth sequences including bubble center, radius, contact line and contact angles over time. Bubble density, nucleation threshold and detachment size, as well as coalescence behavior, were shown significantly different for muscle and fat tissues surfaces, whereas growth rates after a critical size were governed by diffusion as expected. Heterogeneous nucleation was observed from preferential sites on the tissue substrate, where the bubbles grow, detach and new bubbles form in turn. No new nucleation sites were observed after the first 10 min post decompression start so bubble density did not vary after this point in the experiment. In addition, a competition for dissolved gas between adjacent multiple bubbles was demonstrated in increased delay times as well as slower growth rates for non-isolated bubbles.

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