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If it were bends my joints would be hurting—not the middle of my thigh, that’s what all the textbooks say … Textbooks aren’t always right!

Richard Pyle, experienced underwater diver, after suffering decompression sickness

Diving medicine (also known as undersea/hyperbaric medicine) focuses on the diagnosis, treatment and prevention of conditions that occur as a result of a human’s exposure to the underwater environment. Diving is growing in popularity, with an estimated 25 million divers certified worldwide since 1967 and over one million new divers trained annually.1

Diving poses a wide set of physiological challenges and risks. Not only is the pressure of the underwater environment a stressor to the body, but diving often incorporates other challenges, such as cold (see Chapter 24), tides, currents and the patient’s medical history. The sport and exercise medicine clinician may encounter these issues when a patient seeks guidance prior to diving, especially in the setting of a pre-existing medical condition.


There are a number of different disciplines of diving that can expose an individual to risk. These include:

  • scuba diving

  • breath-hold/free diving

  • umbilical (surface-supply) diving

  • rebreather diving.

Scuba (self-contained underwater breathing apparatus) is the most common form of diving and is used in commercial and recreational as well as technical diving. Scuba divers carry their own breathing gas, usually compressed air, allowing greater mobility than surface-supply diving and longer excursions underwater than breath-hold diving. The scuba apparatus is an open-circuit system, meaning that it discharges all the expired gases into the environment upon exhalation. The system consists of one or more diving cylinders containing breathing gas delivered at high pressure, supplied to the diver through a regulator. Although compressed air is by far the most common gas used, some divers will use specifically prepared mixed gases, such as nitrox, a mixture of nitrogen and oxygen, to increase the length of their dives.

Closed-circuit or semi-closed-circuit rebreather scuba systems allow recycling of exhaled gases. The volume of gas used is reduced compared to that of an open circuit; therefore, a smaller cylinder or cylinders may be used for an equivalent dive duration. Rebreathers extend the time spent underwater compared to open circuit for the same gas consumption. They produce fewer bubbles and less noise than scuba, which makes them attractive to covert military divers to reduce the risk of detection, scientific divers, to reduce disturbance of marine life, and media divers, to avoid bubble interference.

Surface-supplied (umbilical) diving is the method whereby the diver’s breathing gas is supplied by an umbilical connection to the surface, either from the shore or from a diving support vessel. The primary advantages of conventional surface-supplied diving are lower risk of drowning and considerably larger breathing gas supply than scuba, allowing longer working periods. It is commonly used in saturation ...

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