Dive Science Demystified: Decompression Illness

It’s a gas, gas, gas

Going back to our installment on gasses, you might remember that atmospheric air, the kind we breathe all the time.

It’s scientifically considering a gas mix, consisting mostly of nitrogen (roughly 78 percent) and oxygen (roughly 21 percent), with a few other gasses taking the last 1 percent.

The oxygen is transported from our lungs, via our blood stream, to our cells (more on this in a later installment), where it is consumed. The nitrogen, however, serves no purpose, and is therefore called an inert gas.

Read more about breathing gases on Nitrox Diving 101: What is Enriched Air Diving?

When we dive, we subject our bodies to increased pressure. The increase in pressure causes our tissues to absorb higher amounts of nitrogen than at the surface. Again, as this is an inert gas, this doesn’t do any harm, nor any good, it just happens.

The potential problem comes when we start surfacing.

Bubble trouble when diving

When ascending, the pressure around us starts to decrease. With that, the nitrogen gas that has been absorbed into our tissue, such as our blood, fat, and muscle tissue, starts to be released again.

As long as we ascend slowly enough, this process can go on without any problems, as the released gas is expelled as we exhale.

Here is another lesson on Slowing Down as if your life depended on it.

Ascend too quickly, and too much gas is released too quickly, and bubbles start to form.

And these bubbles are what can cause the real problems.

Is that a Coke in your veins?

The concept of a gas being absorbed into tissue and then being released in the form of bubbles may seem a bit abstract.

Though most of have seen it happen many, many times in our lives. Every time we open a bottle of soda, beer, or other carbonated drink. As we open it, bubbles form and we can even hear a fizz as the cap releases its seal with the bottle’s neck.

What is happening is that there is a greater pressure inside the bottle, than outside. And as the bottle is opened, that pressure equalizes rapidly, and the gas that was dissolved in the liquid is released and return to its gaseous form.

In this case, it happens so quickly that the bubbles are visible, but if we did it slowly enough, the bubbles would only be microscopical and would be released without being visible to the naked eye.

Think of your blood stream as a bottle of Coke and the gas released as the nitrogen:

• Ascend slowly enough and the bubbles stay microscopic and are released without problems.
• Ascend too quickly, and larger bubble form, too large to be easily released into your lungs and out with the breath.

Effects of decompression illness

These bubbles are then moved around the blood stream, and often get stuck in unwanted places.

Most typically, they clot together at the main joints, such as the shoulder, elbows, knees, or hips, causing joint pain.

Or, they clot together near the skin, causing a rash-like condition. They can also clot together in the brain tissue, near the heart, or block a major artery, which is the very critical.

They can even enter the nervous system.

The result can be anything from an itching sensation and pain, to unconsciousness and even death.

Even if people survive a serious attack of decompression illness, permanent damage to physical or neurological functions is a risk.

Treating decompression illness

The first aid treatment for decompression illness is pure oxygen. This has been known to decrease the size of the bubbles in the body, and in mild cases, may be enough to solve the problem altogether.

For more serious cases, hyperbaric treatment is needed, using a pressure chamber to put the patient under pressure in an oxygen-rich environment to reduce bubble size, and then slowly bringing them back to normal pressure levels.

In severe cases, several treatments may be needed.

In case you or your dive buddy ever experience this, make sure you know exactly how to treat Decompression Illness.