Why should a patient with decompression sickness carried by foot with the head lowermost?

The "theory" regarding moving an individual with decompression sickness ("the bends) with feet elevated above the head is based on the idea that bubbles of gas float in liquid. Here's the idea. Breathing compressed air for "too long" and then surfacing without decompression stops causes gas to come out of solution in the blood and form bubbles. By keeping the head lowered, it is thought that the bubbles will be less likely to make their way to the brain. Bubbles in the circulatory system in the brain (or anywhere else) could block blood flow and, after only a few minutes, cause tissue death. The thinking is that if some tissue is going to die while "the rest" of the affected person survives, a bit of loss in the lower limbs is preferably to the loss of brain tissue. Loss of brain tissue has a catastrophic effect on personality, on the individual's identity, and on cognitive and motor functions. It's devastating. Better to lose, say, a portion of a leg than have one whole side of the body paralyzed. That is the thinking behind the idea.