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
Scuba skills her breath during ascent, which can occur during an emergency free ascent. As lung overexpansion injury is potentially life-threatening, entry level diver training emphasizes developing the habits of not holding one's breath while diving on scuba, and slow continuous exhalation during simulated emergency swimming ascents. Techniques for clearing blocked Eustachian tubes during ascent are also generally taught at entry level. Uncontrolled rate of ascent can increase risk of decompression sickness and lung overexpansion injury even when diving within the no-stop limits of the decompression tables, so the skills of buoyancy control during ascent are important for diver safety and are