Decompression Sickness

Also known as The Bends and Caisson Disease, Decompression Sickness is an illness that can affect divers or other people (such as miners) who are in a situation that involves pressure rapidly decreasing around the body.

DCS, as it is commonly know, is caused by a build up 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 actually harmful and it's quite possible for the body to continue to absorb nitrogen until it reaches a point called saturation, which is the point at which the pressure in the tissues equals the surrounding pressure.

The problem arises when this pressure needs to be released. In order to release the nitrogen slowly from the body, 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 tissue too quickly it becomes bubbles in the body and this leads to Decompression Sickness. The bubbles must normally be on the arterial side of the circulatory system to be harmful - they are usually harmless on the venous side. 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 bisymmetrical symptoms to occur.

Type II Decompression Sickness

Type II Decompression Sickness is the most 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 shows 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

Extreme tiredness is very common in cases of Decompression Sickness and can sometimes be the only symptom of Decompression Sickness present. It is not know 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. This is caused by bubbles forming in the cochlea's perilymph during decompression. The result can be hearing loss, dizziness, ringing of the ears, and vertigo.

Symptoms

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

Every 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:

• Bodyfat
  The theory is that nitrogen absorbs more easily into fat, so an overweight diver is at a greater risk of decompression sickness.
• Exercise
  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.
• Gender
  Theoretically women should have a higher risk of Decompression Sickness due to the fact that women typically have a higher bodyfat 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.
• Age
  Generally, older people are at an increased risk of Decompression Sickness. This is due to less efficient circulatory and respiratory systems.
• Fitness
  Fitness definitely decreases the risk of Decompression Sickness. A fitter body is able to tolerate more physical stress, including Decompression Sickness.
• Dehydration
  Dehydration causes less blood to be available for gas exchange which makes it more difficult for the body to off-gas, increasing the risk of Decompression Sickness.
• Injury and Illness
  Injury and illness can affect normal circulation, increasing the risk of Decompression Sickness.
• Alcohol
  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 bodies ability to transport gas. This will lead to an increased chance of Decompression Sickness.
• Cold
  It is generally believed by doctors that diving in cold water increases the risk of Decompression Sickness. This is due to the body working harder to keep warm as it becomes colder. Meaning that when the body is warmer it is able to absorb gas normally but as it becomes cold it has difficult offing 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.
• Patent 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 that allows blood to bypass the lungs. Normally, this hole would close within a year of birth, but in approximately 20-34 of people this does not happen, leaving a permanent opening in the heart. Usually, 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 that bubbles are more easily able to 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.
• Reverse Profiles
  The jury is still out on reverse profiling, or making a deeper dive after a shallower dive. Theoretically it should increase the risk of Decompression Sickness, but this has not been proven scientifically. It would still be better to err on the side of caution.

Prevention

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 hung-over
• Get checked out by a doctor to find out if you have a PFO
• Avoid reverse profiling - just in case

Treatment

Immediate on the scene treatment consists of oxygen therapy and basic first aid. 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.

References

PADI, Encyclopedia of Recreational Diving, 3rd Edition.

Dive Computers

Dive Computers

Scuba computers are compact digital devices that perform the task of nitrogen management without the need of dive tables. Scuba computers combine a timer with a depth gauge.  These computers run software that computes the absorption of gases within the divers body.  Many recreational divers use scuba computers. While it is essential during training that all divers learn about residual nitrogen and decompression using dive tables, scuba computers will enhance the divers experience as it will perform nitrogen management.   It is important that the diver periodically review the dive tables in the event of computer malfunctions.

It is important to understand that  scuba computer does NOT plan any dives for the diver.  The planning is the responsibility of the one diving  because dive safety must be planned by the diver and not the computer.    All dive certification agencies should promote dive safety.

Dive computers keep track of the following:

• depth and bottom time
• amount of nitrogen present in the diver's body
• alerts the diver if nitrogen levels are getting too high
• informs the diver to make decompression stops if necessary

Traditional dive tables use only maximum depth and time to calculate absorbed nitrogen.   The calculation assumes the diver was at the maximum depth for the entire dive.     This is where we find the benefits of dive computers.   Dive computers do not calculate nitrogen in the same manner used when using dive table.   Dive computers accurately calculate and track the depth allowing the diver to have longer bottom time.   More bottom time means longer dives.

When shopping for a dive computer do consider the following:

• Can the battery be replaced by the diver or must it be serviced to be replaced?
• Can the dive data be uploaded to a computer?
• Can the dive computer handle nitrox gas mixtures as well as air?
• Can the buttons on the computer be managed while wearing neoprene gloves?
• Is the computers interface to the diver's liking?
• Does the dive computer support decompression management?
• Does the dive computer support "time-to-fly" (time you must wait between your last dive and ascending to altitude or flying)?
• Does the dive computer use a well-tested algorithm for calculating gas absorption and decompression?  (Mares-Wienke Reduced Gradient Bubble Model (RGBM) Algorithm,  Buhlmann Algorithm, and etc.)

Always research the dive computer's brand and model before purchasing. Look for recognizable manufacturers and consult the diver magazines and consumer guides.

-Fin For Yourself