The origin and destination of bubbles

With decreasing pressure, a threshold is eventually reached where bubbles start to form in the body; this depends on the amount of inert gas and the extent of decompression. At extreme altitudes, DI cannot be avoided, even after prolonged oxygen pre-breathing 44.

Although decompression bubbles are traditionally classified as intra- or extravascular, this division may be misleading as it does not describe the origin of bubbles but rather where they have been observed. In fact, there is no proof that bubbles form directly in blood vessels. Rather, it is believed that they may be admitted through endothelial gaps as they develop within surrounding perivascular tissues 45. Another mechanism for the intravascular appearance of bubbles is by traumatic introduction during pulmonary barotrauma 46. As little as 10% overexpansion of the lungs is enough to cause gas embolism 47,48. This would occur with an intratracheal pressure of 76-80 mm Hg (or 99.2-108 cm H2O), or during a breath-hold ascent (after breathing compressed gas) from only 3 feet (~1 meter) of seawater to the surface 48. Although traumatic injection of gas vs. bubbles released by inert gas supersaturation represent two completely different etiological mechanisms, they are often difficult to differentiate clinically: physical or radiological evidence of pulmonary injury is often absent in AGE 49, whereas arterialization of inert venous gas emboli may result in arterial gas embolization with clinically indistinguishable results.

Although the origin of bubbles may be ambiguous, their effects are more distinct. Intravascular bubbles embolize tissue causing ischemia 50; they also traverse the microvasculature (so-called "transbolism") and injure endothelium 51; they cause reperfusion injury and vasospasm 18. Bubbles can cause venous stasis, hemorrhage and precipitate plasma protein interactions 52. Extravascular or tissue bubbles disrupt and tear delicate tissues and blood vessels; they can also increase tissue compartment pressures i.e., cause regional compartment syndromes 53.

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