 Over the years, many studies have been conducted on the different aspects of human physiology. It was during the 1800s that showed us the effects of decompression sickness, also known as DCS. After long periods of working at high barometric pressure in caissons beneath the Hudson River, a bridge-building engineer experienced severe pain and muscle cramps. It was through his symptoms we learned that exposure to a change in barometric pressure can cause inert gases, mainly nitrogen, to come out of solution and form bubbles. This early form of decompression sickness was coined caissons disease. More precisely, nitrogen bubbles can form in our body fluids and lodge in various tissues of the body. Altitude decompression sickness in the 1930s became a common problem associated with high altitude balloon and aircraft flight. With today's aviation technology, we are able to fly higher and faster than ever before. However, pilots and passengers are still subject to the stresses of high altitude flight. Most physiological problems associated with flying at high altitude are caused by the drop in atmospheric pressure. This is what exposes the pilot to the possibility of decompression sickness. Certain laws of physics can clarify the occurrence of decompression sickness. Henry's law states, when the pressure of a gas over a liquid is decreased, then the amount of gas dissolved in that liquid will also decrease. This is best demonstrated when you remove the top from a can of soda. You hear the gas escaping and see bubbles form in the soda. These bubbles are the carbon dioxide gas coming out of the solution as a result of sudden exposure to lower barometric pressure. The human body reacts in much the same way. The body stores nitrogen in tissues and fluids. When the body is exposed to decreased barometric pressure, like flying in an unpressurized aircraft to altitude or during an inflight rapid decompression, the nitrogen dissolved in the body comes out of solution. If the nitrogen leaves solution faster than the body can compensate through our respiratory and circulatory systems, then nitrogen bubbles form and lodge in different areas of the body, causing a variety of signs and symptoms. There are specific symptoms for each bubble formation site. The different locations represent different types of decompression sickness. There are four types of decompression sickness and each has a different effect on the body. Benz is pain in and around the large joints of the body and is the most common type of decompression sickness in aviation. It's described as a localized deep pain aggravated by movement of the joint, ranging from mild to excruciating. There is also evidence that Benz, once experienced, may recur in the same location during subsequent exposures. Benz that persists during descent or reappear at ground level can be a serious condition if left untreated. Skin manifestations is another type of decompression sickness. Symptoms include tingling, itching and cold or warm sensations. These symptoms are caused by the occurrence of bubbles localized under the skin. A modeled or marbled pattern may appear on the skin around the shoulders, upper chest and abdomen. The chokes is a DCS term related to the chest and lungs. This is where the bubbles intrude on pulmonary vessels. Symptoms may include a burning sensation in the chest, progressing to pain associated with deep breathing. Later stages of this type of DCS involve feelings of suffocation. Although the chokes occur infrequently, the condition is quite serious and if allowed to progress can result in collapsing and unconsciousness. Neurological manifestations is another type of decompression sickness. This is a very serious type of decompression sickness and can result in death. It affects the nervous system including the brain, spinal cord and peripheral nerves. Some symptoms include headache, visual disturbances, unexplained fatigue, muscle weakness or paralysis. Now let's look at those factors that make you more susceptible to developing altitude induced decompression sickness. There is no specific altitude that can be considered as an exposure threshold for decompression sickness, but here are some guidelines for aviators to consider. Most pilots have little risk of decompression sickness below 18,000 feet MSL, provided they have not been scuba diving within the last 24 hours. Most aviation cases of decompression sickness occur at or above 25,000 feet MSL. Repetitive exposure to altitudes above 18,000 feet within a short period of time increases the risk of developing decompression sickness. The faster the rate of ascent to altitude, the greater the risk. The longer you are at altitude, the greater the risk for decompression sickness. There appears to be some evidence that age increases the risk of decompression sickness. Research indicates that having a recent joint or limb injury may predispose an individual to developing the bends. Exposure to very cold temperatures increases the risk of decompression sickness. A high ratio of body fat increases the risk of developing decompression sickness. A person who is physically active while flying at 18,000 feet or above is at greater risk for decompression sickness. The after effects of alcohol consumption, such as dehydration, increase the susceptibility to decompression sickness. Scuba diving requires breathing air under increased atmospheric pressure. Under these conditions, the amount of nitrogen stored in the body increases. Enough time should be allowed to eliminate the excess nitrogen stored in the body. Cami recommends 24 hours between scuba diving and flying. The following steps should be taken if there is a suspected case of decompression sickness. If available, go on 100% oxygen immediately. If possible, minimize movement of the affected part of the body. Declare an emergency and land as soon as possible. Even if symptoms disappear, land and seek qualified medical attention. Continue to breathe 100% oxygen if possible. After landing, seek medical assistance from an FAA aviation medical examiner, a military flight surgeon, or a hyperbaric medicine specialist. Not all physicians are familiar with the handling of decompression sickness cases. Be your own advocate. Medical treatment may involve the use of a hyperbaric chamber, also known as a dive or compression chamber, operated by specially trained personnel. It is important to remember that decompression sickness can occur after you've returned a ground level. Familiarize yourself with your local aviation medical examiner and the availability of a hyperbaric chamber in your area of operations. To obtain information on hyperbaric facilities to treat decompression sickness emergencies, contact the Divers Alert Network, or DAN. Decompression sickness, also referred to as DCS, occurs when the body is exposed to a decreased barometric pressure and the nitrogen dissolved in the body comes out of solution and forms bubbles. There are four types of DCS. The bends, pain localized in large joints, skin manifestations, tingling, itching, and cold or warm skin sensation. The chokes, a deep burning chest pain aggravated by breathing. Neurological manifestations, headache, visual disturbances, unexplained fatigue, muscle weakness, or paralysis. The factors that make you more susceptible to developing decompression sickness, exposure to high altitude, repetitive exposure to altitudes above 18,000 feet, high rate of ascent, prolonged time at altitude, age, previous injury, low ambient temperature, overweight, physical activity in flight, alcohol use, scuba diving before flying. If you suspect a possible case of decompression sickness, if available, go on 100% oxygen immediately. If possible, minimize the movement of the affected part of the body. Declare an emergency and land the aircraft as soon as possible. Even if your symptoms disappear, land and seek qualified medical attention. Continue to breathe 100% oxygen if possible. Remember that any time you fly above 18,000 feet in an unpressurized aircraft or experience a rapid decompression, you are at risk of developing decompression sickness. So be prepared for the unexpected.