Decompression Sickness: Into the Unknown

Aliases: decompression sickness, DCS, the bends, caisson disease

Exploring wouldn’t be an adventure without risk, and the brave few who push exploration to its limits, diving into our planet’s depths or rocketing out of our atmosphere, are certainly taking their chances. Voyagers to extreme environments, like astronauts or deep-sea divers, can suffer from many unusual ailments, including decompression sickness (DCS), also know as “the bends”. DCS is a condition with a litany of symptoms (see below) that arises from a hyperbaric exposure– that is, being in a high or low-pressure environment, like the deep ocean or outer space.

While exploring, excess gas (usually nitrogen) is stored in body tissues and upon returning to earth’s normal surface pressure, it is released, potentially leading to all kinds of issues. The greater the amount of pressure change the body experiences and the longer that experience lasts, the more gas is sequestered, and the more gradually the person must be brought back to normal surface pressure3. Historically, DCS has been a big problem for people working at high pressures, such as tunnel workers, peaking at an incidence rate of 24%. Greater awareness and new technology has markedly reduced it; only 5 out of every 10,000 (0.05%) of modern recreational dives result in DCS2.

Although great strides have been made in eliminating DCS, there is room for improvement. Current decompression tables, which dictate the rate of return to normal pressure after a hyperbaric exposure, were developed in 1971, and need updating1. In part, the issue is DCS itself: the condition remains mysterious. It’s still unclear how and where gas storage happens in the body, making accurate predictions about the effects of decompression difficult2. It turns out, if you venture into the unknown, you might bring a piece of it back with you.

decompression sickness
Good under pressure.

Cause: When a person breathes air that is either under much greater or much less pressure than it is at the earth’s surface, excess gas is stored in their tissues. When they return to breathing air at normal surface pressure, the body wants to expel the gas, and it will be released from the tissue into the bloodstream to eventually be exhaled3.

Consequence: After a hyperbaric exposure, the excess gas released into the bloodstream can form bubbles that interfere with blood flow and tissue oxygenation. This can lead to an impressive suite of symptoms, including mottling of the skin, joint pain, numbness or tingling, coughing or shortness of breath, dizziness, itching, fatigue, loss of coordination, tremors, weakness, paralysis, and collapse or unconsciousness3. Symptoms usually appear within 24 hours, but can take up to two days. Typically, the first sign of DCS is a dull, aching pain that can only be localized to a general region of the body. Mild cases often go unreported, and resolve themselves. More severe cases typically cause pain (20-50% of cases) and neurological symptoms, such as numbness (20-40% of symptoms)2. DCS can be very painful and– in the worst instances– fatal1.

Cure: There is no hard and fast cure for DCS. The condition is typically treated with recompression therapy, where patients are put in a pressurized room to redissolve the gas that has been released into their bloodstream, removing the bubbles. Hyperbaric oxygen therapy (HBO), breathing pure oxygen in a pressurized room, is also commonly used. HBO prevents further gas uptake, and accelerates the removal of stored excess gas and the delivery of oxygen to potentially deprived tissues throughout the body. Prevention is critical in combatting DCS. Workers that are regularly exposed to high or low pressure environments use decompression chambers, rooms where the pressure is controlled, to gradually bring themselves back to surface pressure. The same principle is followed when divers resurface slowly, allowing time for their bodies to readjust. Exercise and being fit can prevent its onset, as can oxygen prebreathing, which rids the body’s tissues of nitrogen and reduces bubble formation2.


  1. Decompression Sickness and Tunnel Workers. Centers for Disease Control and Prevention. 19 September 2012. Web. 15 October 2014.
  1. Mahon, RT, & DP Regis. (2014). Decompression and decompression sickness. Comprehensive Physiology, 4: 1157-1175.
  1. Scuba diving. Centers for Disease Control and Prevention. 1 August 2013. Web. 15 October 2014.

Image source: Wikimedai Commons,

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Suzi Claflin

I am a postdoctoral fellow studying chronic disease epidemiology.

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