The Science and Medicine of Decompression Illness

IMG_0158All About Decompression Sickness

Causes, Types, and Symptoms

Decompression Sickness (DCS), also known as “The Bends” and “Caisson Disease,” can affect divers or people like miners who are in a situation that involves rapid pressure decreases around the body.
DCS is caused by a buildup of nitrogen bubbles in the body. When we breathe, approximately 79 of the air we’re breathing is nitrogen. As we descend in water, the pressure around our bodies increases, causing nitrogen to be absorbed into our body tissues. This is not harmful and it’s possible for the body to continue to absorb nitrogen until it reaches a saturation point. That is when the pressure in the tissues equals the surrounding pressure.
A problem arises when the nitrogen needs to be released. A diver must ascend slowly and carry out decompression stops if necessary – this allows the nitrogen to slowly seep out of the body tissues and either immediately revert to being a gas or to become tiny harmless bubbles which will eventually become revert to gas. This process is called “Off-gassing” and is normally carried out through the lungs.
If a diver ascends too fast and the nitrogen escapes the body tissues too quickly, it becomes bubbles in the body and this leads to Decompression Sickness. There are several types of Decompression Sickness:
Type I Decompression Sickness

Type I Decompression Sickness is the least serious form of Decompression Sickness. It normally involves only pain in the body and is not immediately life threatening. It is important to note that symptoms of Type I Decompression Sickness may be warning signs of more serious problems.

  • Cutaneous Decompression Sickness
: This is when the nitrogen bubbles come out of solution in skin capillaries. This normally results in a red rash, often on the shoulders and chest.
  • Joint and Limb Pain Decompression Sickness
: This type is characterized by aching in the joints. It is not known exactly what causes the pain as bubbles in the joint would not have this effect. The common theory is that it is caused by the bubbles aggravating bone marrow, tendons, and joints. The pain can be in one place or it can move around the joint. It is unusual for symptoms to occur on both sides of the body.

Type II Decompression Sickness

Type II Decompression Sickness is the more serious and can be immediately life-threatening. The main effect is on the nervous system.

  • Neurological Decompression Sickness: 
When nitrogen bubbles affect the nervous system they can cause problems throughout the body. This type of Decompression Sickness normally presents as tingling, numbness, respiratory problems, and unconsciousness. Symptoms can spread quickly and if left untreated can lead to paralysis or even death.
  • Pulmonary Decompression Sickness: This is a rare form of Decompression Sickness that occurs when bubbles form in lung capillaries. Fortunately, the majority of the time bubbles dissolve naturally through the lungs. However, it is possible for them to interrupt blood flow to the lungs which can lead to serious and life-threatening respiratory and heart problems.
  • Cerebral Decompression Sickness
: It is possible for bubbles that make their way into the arterial blood stream to move to the brain and to cause an arterial gas embolism. This is extremely dangerous and can be identified by symptoms such as blurred vision, headaches, confusion, and unconsciousness.

Other Forms of Decompression Sickness

3 (1)Extreme tiredness is very common in cases of Decompression Sickness and can sometimes be the only symptom of Decompression Sickness present. It is not known what causes this but you should be aware that extreme fatigue could be a sign of more serious problems. It is also possible for Decompression Sickness to occur in the inner-ear. The result can be hearing loss, dizziness, ringing of the ears, and vertigo.


Decompression Sickness can manifest itself in many different ways and has many different symptoms, but the most common symptoms are:

  • Extreme Fatigue
  • Joint and Limb Pain
  • Tingling
  • Numbness
  • Red Rash on Skin
  • Respiratory Problems
  • Heart Problems
  • Dizziness
  • Blurred Vision
  • Headaches
  • Confusion
  • Unconsciousness
  • Ringing of the Ears
  • Vertigo

Stomach Sickness


Risk Factors

IMG_0252Every diver has a different level of risk of Decompression Sickness. Many risk factors are still not fully understood, but there are a few basic factors that doctors agree increase the chance of developing Decompression Sickness:

: The theory is that nitrogen absorbs more easily into fat, so an overweight diver is at a greater risk of decompression sickness.

Interestingly, exercise has both a positive and negative effect. Exercise at least 12 hours before a dive seems to produce proteins that protect the body and decrease the risk of Decompression Sickness. On the other hand, exercise less than 12 hours before a dive can raise the number of gas micronuclei on which bubbles form and this increases the risk of Decompression Sickness. Exercise immediately after a dive increases the risk of bubbles forming as blood pressure is increased and bubbles can more easily be transferred from the venous to the arterial side of the circulatory system.

: Theoretically women should have a higher risk of Decompression Sickness due to the fact that women typically have a higher body fat content. However, this has not been proven in studies and it’s possible that gender does not affect the chances of suffering from Decompression Sickness.

Generally, older people are at an increased risk of Decompression Sickness. This is due to less efficient circulatory and respiratory systems.

Fitness definitely decreases the risk of Decompression Sickness. A fitter body is able to tolerate more physical stress, including Decompression Sickness.

: Dehydration causes less blood to be available for gas exchange which makes it more difficult for the body to off-gas nitrogen, increasing the risk of Decompression Sickness.

Injury and Illness: 
Injury and illness can decrease normal circulation, increasing the risk of Decompression Sickness.

: Consuming alcohol before or after a dive accelerates circulation which helps tissues to load with gas. Alcohol also dilates capillaries which can increase the rate of nitrogen released.

Carbon Dioxide: 
Improper breathing can lead to elevated levels of carbon dioxide which interferes with the body’s ability to transport gas. This will lead to an increased chance of Decompression Sickness.

Doctors generally believe diving in cold water increases the risk of Decompression Sickness. This is due to the body working harder to keep warm. When the body is warmer it is able to absorb gas normally but as it becomes cold it has difficulty removing the gas.

Altitude and Flying After Diving: 
When ascending on land or in a plane, the atmospheric pressure changes and this increases the chances of Decompression Sickness. It is best not to ascend above 300 meters (1000 feet) or fly after diving. Consult the current flying after diving guidelines to know when it is safe to fly.

IMG_0249Patent Foramen Ovale (PFO) – Hole in the Heart
: As a fetus, a baby doesn’t breathe and needs a way for blood to bypass the lungs until it is born. The body achieves this by having a small opening in the middle of the heart. Normally, this hole closes within a year of birth, but in approximately 33 percent of people this does not happen, leaving a permanent opening in the heart. Normally, a flap grows over the opening and there is no effect. However, in some cases the flap allows blood to pass through the opening. This means bubbles can pass from the venous to the arterial side of the circulatory system, greatly increasing the risk of Decompression Sickness. It has been found that a large proportion of divers who suffered from Decompression Sickness had a PFO.



As there are many risk factors, there are also many methods of prevention. Here’s a basic checklist that will help you lower your risk of suffering from Decompression Sickness:

  • Always ascend slowly and safely from every dive
  • Don’t push your limits and do all required decompression stops
  • Keep physically fit and within a healthy weight range
  • Don’t exercise within 12 hours of diving
  • Don’t ascend to altitude or fly immediately after diving
  • Breathe normally throughout the dive, don’t exert yourself or skip breathe
  • Make sure you’re adequately hydrated before every dive
  • Don’t drink alcohol before or after diving and never dive when hungover
  • Get checked out by a doctor to find out if you have a PFO—most doctors do not recommend this, just because it is expensive and can be invasive. And divers would have to be willing to quit diving if they found out they had it. Up to you, though.
  • Avoid reverse profiling – just in case


Immediate on the scene treatment consists of oxygen first aid and basic life support. This should be followed as quickly as possible by recompression treatment in a recompression chamber. When treating Decompression Sickness the delay in beginning recompression treatment can be the biggest single cause of residual effects.


Source material; PADI, Encyclopedia of Recreational Diving, 3rd Edition,, et el.