Just as people often feel pressure when flying in airplanes, professional and recreational divers are well aware of the drastic change in pressure as they descend into the water and return to the surface. Airplanes are pressurized, however, and the passengers usually experience only mild changes in air pressure as compared to divers, who may experience pressure changes many times greater than normal atmospheric pressure.

Unfortunately for divers, ascending too rapidly from depths greater than about 30 ft (9 m) can result in decompression sickness, also called dysbarism, caisson disease, the bends, and compressed air illness. When a diver remains at depth for sufficiently long periods of time, gases, especially nitrogen, accumulate in the body tissues. If the diver surfaces too quickly, these nitrogen gases expand and form bubbles in various parts of the body. Mild cases involve only tingling of the skin, dizziness, or slight disorientation. When...