Saturday, June 15, 2024

Dysbarism

Background

Although dysbarism includes problems associated with high altitude and aerospace endeavors, dysbarism also relates to the increasing pressures of descending under water that are usually experienced in free or assisted dives. Exposure to the physiologic effects of pressure during descent also can be experienced in submarines during emergencies and in tunneling projects.

Since 4500 BCE, humans have engaged in free (breath-hold) diving to obtain food and substances from shallow ocean floors at depths of 100 ft or more. The 2007 record-setting breath-hold unlimited dive of Herbert Nitsch to 702 ft (214 m) (21.7 ATM) attests to this human feat.
At this depth, the lungs are only 4.6% of their normal size. To emphasize the extreme nature of this record, Mr. Nitsch attempted to break his own record on June 6, 2012. He descended to a depth of 819 ft (250 m) (25.2 ATM). However, on ascent, he blacked out due to narcosis and had an uncontrolled ascent to 33 ft (10 m), where rescue divers were prepositioned. He suffered severe neurologic decompression sickness.

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 of these early diving methods required a physical connection to a support platform or boat. The Aqua-Lung, developed by Cousteau and Gagnan in 1943, and the submarine escape appliances, developed by Momsen and Davis in the 1930s, were the forerunners of today’s self-contained underwater breathing apparatus (SCUBA) that frees divers from the limitations of tethering.

The increasing popularity of scuba diving and growth of commercial diving is increasing the incidence of exposures to deep pressures. Moreover, even far from the coasts, more individuals are diving in quarries, lakes, rivers, and caves. Add to this the ability to travel rapidly from anywhere in the world in a matter of hours (and the exacerbation of dysbarism caused by decreased pressures in flight), and the potential for dysbaric events can be appreciated. For these reasons, all physicians, especially emergency physicians, worldwide should maintain an expectation and knowledge of the physiologic effects and management of dysbaric injuries.

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