Keith Parrish, age 12, of High Point, N.C., for his question:
WHAT ARE THE BENDS?
Pneumatic caissons are used in digging underwater tunnels and other projects that require watertight chambers. Air pressure in the caisson balances outside water pressure, keeping the water out of the working area. Caissons cannot be opened directly to the outer air since this would allow the compressed air to escape. An air lock is used to hold the pressurized air and also to protect the workers.
Bends is a painful condition that is caused by the formation of nitrogen bubbles in the blood stream and body tissues. Bends will happen when the air pressure surrounding the body is lowered too rapidly. The condition is also called caisson disease or aeroembolism.
Caisson workers and deep sea divers sometimes suffer bends when they return to the earth's surface. Fliers sometimes also suffer from the bends if they go too quickly to a very high altitude when the pressure outside of the body is lowered, nitrogen and other gases bubble out of the body fluids. In the same way, the air bubbles form and escape when a pan of cold water is heated.
If the outside pressure is lowered too fast, the gas bubbles form in the blood vessels and tissues. The ressult is a tingling of the skin and alternate hot and cold sensations, followed by pain and loss of muscular control. Pain is usually noticed first in the joints, then the chest, abdomen and finally along the nerve trunks. Unconsciousness and death may often result from the bends.
Caisson workers avoid the bends by passing to and from their work through a sealed chamber called an air lock. Air pressure is gradually increased or decreased within the air lock. This prevents the forming of nitrogen bubbles.
Bends can be treated by putting the patient in a sealed pressure chamber. The pressure within is raised, and then lowered gradually. This causes the nitrogen bubbles in the blood to disappear.
Bends can be largely prevented by breathing pure oxygen immediately before ascent, and by continuing to breathe pure oxgyen during ascent. This removes a large amount of nitrogen from the body. This method is often used in aircraft.
Except in the most serious cases, an attack of the bends can usually be remedied promptly by a return to the higher pressures in lower altitudes, if passengers on a plane have a problem.
By means of tests in low pressure chambers, it can be determined which persons are especially likely to get attacks of the bends, so that they can be kept out of diving work or high altitude flying.