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 practice to three minutes long. A study by Divers Alert Network in 2004 suggests that addition of a deep (c. 15 m) as well as a shallow (c. 6 m) safety stop to a theoretically no-stop ascent will significantly reduce decompression stress indicated by precordial doppler detected bubble (PDDB) levels. The authors associate this with gas exchange in fast tissues such as the spinal cord and consider that an additional deep safety stop may reduce the risk of spinal cord decompression sickness in recreational diving. A follow-up study found that the optimum duration for the deep safety stop under the experimental