History of decompression research and development gets too high when compared to the ambient pressure. These bubbles, and products of injury caused by the bubbles, can cause damage to tissues known as "decompression sickness" or "the bends". The immediate goal of controlled decompression is to avoid development of symptoms of bubble formation in the tissues of the diver, and the long-term goal is to also avoid complications due to sub-clinical decompression injury. The symptoms of decompression sickness are known to be caused by damage resulting from the formation and growth of bubbles of inert gas within the tissues and by blockage of arterial blood supply to
Decompression sickness are required, but, since helium does not cause narcosis, it is preferred over nitrogen in gas mixtures for deep diving. There is some debate as to the decompression requirements for helium during short-duration dives. Most divers do longer decompressions; however, some groups like the WKPP have been pioneering the use of shorter decompression times by including deep stops. Any inert gas that is breathed under pressure can form bubbles when the ambient pressure decreases. Very deep dives have been made using hydrogen-oxygen mixtures (hydrox), but controlled decompression is still required to avoid DCS. DCS can also be caused at a