Expansion of bubbles under a pulsatile flow regime in decompressed ovine blood vessels

• Active spots on blood vessels produced decompression bubbles under a flow regime.
• There were single-bubble and multi-bubble active spots.
• Bubble expansion from a diameter of 0.1 to 1 mm took 2–24 min at 620 kPa and lower.
• Growth rate was reduced in adjacent bubbles surrounded by others.
• Fast growth (2–24 min) governed by diffusion was preceded by a slow phase (>1 h).

After decompression of ovine large blood vessels, bubbles nucleate and expand at active hydrophobic spots on their luminal aspect. These bubbles will be in the path of the blood flow within the vessel, which might replenish the supply of gas-supersaturated plasma in their vicinity and thus, in contrast with our previous estimations, enhance their growth. We used the data from our previous study on the effect of pulsatile flow in ovine blood vessels stretched on microscope slides and photographed after decompression from hyperbaric exposure. We measured the diameter of 46 bubbles in 4 samples taken from 3 blood vessels (pulmonary artery, pulmonary vein, and aorta) in which both a “multi-bubble active spot” (MBAS)—which produces several bubbles at a time, and at least one “single-bubble active spot” (SBAS)—which produces a single bubble at a time, were seen together. The linear expansion rate for diameter in SBAS ranged from 0.077 to 0.498 mm/min and in MBAS from 0.001 to 0.332 mm/min. There was a trend toward a reduced expansion rate for bubbles in MBAS compared with SBAS. The expansion rate for bubbles in an MBAS when it was surrounded by others was very low. Bubble growth is related to gas tension, and under a flow regime, bubbles expand from a diameter of 0.1 to 1 mm in 2–24 min at a gas supersaturation of 620 kPa and lower. There are two phases of bubble development. The slow and disperse initiation of active spots (from nanobubbles to gas micronuclei) continues for more than 1 h, whereas the fast increase in size (2–24 min) is governed by diffusion. Bubble-based decompression models should not artificially reduce diffusion constants, but rather take both phases of bubble development into consideration.