Scuba Diving: 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.

People involved with tunneling projects and those in submarines during emergencies may also experience the physiologic effects of decreased pressure brought on by such ascents.

Since 4500 BCE, humans have engaged in free (breath-hold) diving to obtain food and substances from shallow ocean floors at depths of 100 or more feet. The 1994 record-setting breath-hold dive of Ferreras-Rodriguez to 417 feet attests to this human feat. Humans began experimenting with crude diving bells as early as 330 BCE. These bells were submerged containing only air. In 1690, the first diving bell with a replenishing air supply was tested. The first crude underwater suit dates back to 1837, and helium was first used in place of nitrogen in 1939.

All these early diving methods required a physical connection to a support platform or boat. The Aqua-Lung, developed by Cousteau and Gagnon, and the submarine escape appliances, developed by Momsen and Davis in the 1930s, were forerunners of the Self Contained Underwater Breathing Apparatus (SCUBA), which frees divers from the limitations of tethering.

The increasing popularity of scuba diving and the growth of commercial diving have increased the frequency of deep-pressure injuries. Even in regions far from coasts, individuals are diving in quarries, lakes, rivers, and caves. In addition, the ability to travel rapidly between areas of disparate altitudes in a matter of hours (including the exacerbation caused by decreased pressures in flight) increases the chance of experiencing decompression injuries. Emergency physicians worldwide should know the physiologic effects and management of decompression sickness.

Pathophysiology: Changes in pressure affect only compressible substances in the body. The human body is made primarily of water, which is noncompressible; however, the gases of hollow spaces and viscous organs and those dissolved in the blood are subject to pressure changes. Physical characteristics of gases are described by the following 4 gas laws, which quantify the physics and problems involved in descending under water.

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