Health A-Z

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What Is It?

Decompression sickness, also called generalized barotrauma or the bends, refers to injuries caused by a rapid decrease in the pressure that surrounds you, of either air or water. It occurs most commonly in scuba or deep-sea divers, although it also can occur during high-altitude or unpressurized air travel. However, decompression sickness is rare in pressurized aircraft, such as those used for commercial flights.

When you scuba dive with compressed air, you take in extra oxygen and nitrogen. Your body uses the oxygen, but the nitrogen is dissolved into your blood, where it remains during your dive. As you swim back toward the surface after a deep dive, the water pressure around you decreases. If this transition occurs too quickly, the nitrogen does not have time to clear from your blood. Instead, it separates out of your blood and forms bubbles in your tissues or blood. It is these nitrogen bubbles that cause decompression sickness. The condition is called the bends because joint pain, a common symptom, can double you over.

What happens inside your body during decompression sickness is similar to what happens when you open a carbonated drink. When you open the can or bottle, you decrease the pressure surrounding the beverage in the container, which causes the gas to come out of the liquid in the form of bubbles. If nitrogen bubbles form in your blood, they can damage blood vessels and block normal blood flow.

Factors that put you at higher risk of decompression sickness include:

  • Heart muscle birth defects, including patent foramen ovale, atrial septal defect and ventricular septal defect

  • Being older than 30

  • Being female

  • Low cardiovascular fitness

  • High percentage of body fat

  • Use of alcohol or tobacco

  • Fatigue, seasickness or lack of sleep

  • Injuries (old or current)

  • Diving in cold water

  • Lung disease

Someone with an abnormal hole or opening in the heart from a birth defect is at especially high risk of developing serious symptoms from decompression illness. Because bubbles create high blood pressure in the lungs, blood and bubbles from your veins may flow more readily through the heart's opening. This means your blood can re-circulate into arteries without first getting oxygen. An opening in the heart can also allow a relatively large air bubble (called an air embolism) to circulate into your arteries. An air embolism can cause a stroke.

People with asthma or another lung disease may have thin-walled air pockets in their lungs called bullae. These pockets do not empty quickly when the persons exhales. As they return to the surface after a deep dive, air in the bullae may expand. If a bulla ruptures, it could cause a collapsed lung or allow a large air bubble (air embolism) to enter the arteries.

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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