How does the increasing pressure affect the amount of gas dissolved in the scuba divers blood?

There are two principal ways that gas solubility affects Scuba divers:

Narcosis. The lipid solubility of gas determines the narcotic effect at depth. For most divers, this is not really noticeable until they reach about 100 feet in depth, when they start to suffer to a greater or lesser degree from narcosis (often misleadingly called "Nitrogen narcosis", or "rapture of the deep"). Technical divers who go to greater depths often use helium gas mixes - due to the very low lipid solubility of helium, it has very little narcotic affect, leaving the diver clear headed.

Decompression sickness. Breathing gases under pressure causes the body to also absorb those gases. If a diver stays at depth for a long time, her tissues can absorb a great deal of gas, and if she ascends too quickly, bubbles can form in her bloodstream, which leads to decompression sickness (also called "the bends" or "caisson's disease"). Divers can avoid DCS by either breathing oxygen rich mixtures like nitrox (the body metabolises oxygen, so it doesn't get absorbed) or limiting their depth or bottom teams to avoid excessive gas absorbtion. Divers who stay too deep or too long need to make decompression stops at shallow depths before surfacing, to allow the gas to diffuse out of their tissues safely.