What Exactly is Decompression Illness?

Physiologically speaking, our bodies, while on the surface, breathe in a mixture of approximately 21% Oxygen and 79% Nitrogen. This is the same mixture of air that scuba divers breathe from scuba tanks, contrary to the assumption of many non-divers that tanks are filled with pure Oxygen.

Our bodies metabolize Oxygen, which aids and facilitates in the transport of blood throughout the body. However, Nitrogen is a neutral gas or physiologically inert, not used by the body. While on the surface, our bodies are saturated with Nitrogen, meaning we hold an amount of Nitrogen equal to the surrounding pressure.

The ambient pressure at the surface is equal to one atmosphere. While on the surface our bodies naturally diffuse Nitrogen. However, at depth or with increased ambient pressure, Nitrogen absorption increases and diffusion decreases, thus creating a higher concentration of sustained Nitrogen in the tissues. While at depth, the body eliminates excess Nitrogen by forming microscopic bubbles referred to as “micro-bubbles” or “silent bubbles.”

These small bubbles are harmless if a diver stays within the depth and time limits provided in the recreational dive planner tables.

However, if dive depth and time limits are exceeded, the body runs the risk of becoming “super-saturated” and unable to safely eliminate Nitrogen absorption as the diver returns to the surface. At this time the number of silent bubbles increases and begins to attach to other bubbles forming large bubbles that expand as ambient pressure decreases. The formation of these large bubbles can occur anywhere in the body, forming in the blood vessels and tissues, which in turn causes Decompression Illness.