The earliest descriptions of DCS used the term “bends” for joint and/or skeletal pain; “chokes” for breathing problems; and “staggers” for neurological problems. In 1960, Golding introduced the terms Type 1 for symptoms involving skin, musculoskeletal system and/or lymphatic system; and Type 2 for the more serious symptoms where the CNS was involved. However, neurological symptoms may develop after the initial presentation of Type 1 DCS. For this reason both Type 1 and 2 DCS have the same initial treatment protocol. In fact, symptoms may appear any time between surfacing and 72 hours.
Due to the potential severity of DCS much research has gone into preventing and treating it. Prevention methods include scuba divers using dive tables and/or computers to limit their exposure to pressure and their ascent speed.
DCS commonly refers to a specific type of scuba diving hazard but may also result from other types of depressurization events (snorkeling, free diving, etc.) Caisson disease is seen in workers decompressing from the watertight structures (caissons) used for working under water in the construction of bridges, dams, the repair of ships, etc.
Flying in unpressurized aircraft, or sudden depressurization of an aircraft also causes DCS, as does extra-vehicular activity (EVA) from spacecraft. EVA includes work done by an astronaut away from the Earth and outside a spacecraft like spacewalks, moonwalks, and repairs done in space. Astronauts on the International Space Station preparing for EVA remain at low atmospheric pressure, 10.2 psi (pounds per square inch or 0.70 bar) for eight hours before their space walk. During the EVA they breathe 100% O2 in their space suits which operate at 4.3 psi (0.30 bar).
For many other medical conditions the therapeutic principle of HBOT lies in its ability to drastically increase partial pressure of O2. Partial pressure refers to the pressure that the gas would have if it alone occupied the volume under consideration. The O2 partial pressures achievable using HBOT are much higher than those present while breathing pure O2 at norobaric (normal barometric pressure equivalent to that at sea level).
Another therapeutic effect is the increased oxygen transport capacity of the blood. Under norobaric conditions O2 transport is limited by the O2 binding capacity of hemoglobin in the red blood cells (rbc’s). Hemoglobin (Hb, Hgb) is the iron-containing oxygen transport metalloprotein that transports O2 from the lungs to tissues all over the body. When it releases O2 (and other chemicals) it picks up the used O2 (carbon dioxide or CO2). Under normal pressures very little O2 is transported by the blood plasma. Blood plasma comprises 55% of blood volume and is composed of 90% water. Blood cells are suspended in the blood plasma. However, plasma stimulated by HBOT can significantly increase O2 transport.
The incidence of DCS is considered rare at 2.8 cases per 10,000 dives. The risk is 2.6 times greater for males than females. DCS affects about 1,000 U.S. scuba divers per year. In the U.S., it is common for medical insurance not to cover treatment for DCS that is a result of recreational diving. A typical stay in a recompression chamber can easily cost several thousand dollars, even before emergency transportation is included. Groups such as DAN offer insurance policies that specifically cover all aspects of treatment for DCS at rates of less than $100/year.