Dr. Charles "Pat" Davis, MD, PhD, is a board certified Emergency Medicine doctor who currently practices as a consultant and staff member for hospitals. He has a PhD in Microbiology (UT at Austin), and the MD (Univ. Texas Medical Branch, Galveston). He is a Clinical Professor (retired) in the Division of Emergency Medicine, UT Health Science Center at San Antonio, and has been the Chief of Emergency Medicine at UT Medical Branch and at UTHSCSA with over 250 publications.
The bends, also known as decompression sickness (DCS) or Caisson disease occurs in scuba divers or high altitude or aerospace events when dissolved gases (mainly nitrogen) come out of solution in bubbles and can affect just about any body area including joints, lung, heart, skin and brain.
Decompression sickness (DCS) is caused by the formation of bubbles of gas that occur with changes in pressure during scuba diving. It is also experienced in commercial divers who breathe heliox (a special mixture of oxygen and helium), and astronauts and aviators that experience rapid changes in pressure from sea level. Scuba diving will be the focus of this article as it is the most common activity that may result in the bends.
Scuba diving is a sport and hobby that continues to increase in popularity each year. There are several organizations that certify individuals to become recreations divers, two of which are PADI (The Professional Association of Diving Instructors) and NAUI (The National Association of Underwater Instructors).
Data collected by Divers Alert Network (DAN) and presented in 2010 revealed 41 cases of DCS out of 137,451 dive profiles collected. It is important to know that even divers that follow decompression schedules and tables may still experience DCS.
The Bends Causes
Nitrogen from a diver's air tank increases in pressure as a diver descends. For every 33 feet in ocean water, the pressure due to nitrogen goes up another 11.6 pounds per square inch,. As the pressure due to nitrogen increases, more nitrogen dissolves into the tissues. The longer a diver remains at depth, the more nitrogen dissolves. Unlike the oxygen in the air tank a diver uses to swim underwater, the nitrogen gas is not utilized by the body and builds up over time in body tissues. The underlying cause of symptoms throughout the body is due mainly to nitrogen bubbles being released and blocking blood flow and disrupting blood vessels and nerves by stretching or tearing them. They may also cause
emboli, blood coagulation and the release of vasoactive compounds.
A clear example to illustrate this bubble formation process is that of a bottle of carbonated soda. A bottle of carbonated soda is filled with gas (carbon dioxide), which cannot be seen because it is dissolved in solution under pressure. When the bottle is opened, the pressure is released and the gas leaves the solution in the form of bubbles. A diver returning to the surface is similar to opening the bottle of soda. As a diver swims to the surface, the pressure due to nitrogen decreases. The nitrogen, which has dissolved in tissues, wants again to leave, because the body can hold only a certain amount based on that nitrogen pressure.
If a diver surfaces too fast, the excess nitrogen will come out rapidly as gas bubbles. Depending on which organs are involved, these bubbles produce the symptoms of decompression sickness.
The risk of decompression illness is directly related to the depth of the dive, the amount of time under pressure, and the rate of ascent. Dive tables, such as the US Navy Dive Tables, provide general guidelines as to what depths and dive times are less risky for the development of decompression sickness.
Although decompression sickness (DCS), a complex resulting from changed barometric pressure, includes high-altitude–related and aerospace-related events, this article focuses on decompression associated with the sudden decrease in pressures during underwater ascent, usually occurring during free or assisted dives.