Decompression Sickness or The Bends is one of the main risks in diving, so it's important to understand what it is and how we can try to avoid it.
The difference between DCI and DCS.
Decompression Illness or DCI is an umbrella term that includes both Decompression Sickness (DCS) and Lung Overexpansion Injuries. In this article, we will look at Decompression Sickness in basic and simple terms so it's easy to understand!
What is Decompression sickness?
To put it simply – it is gas coming out of solution due to a reduction of pressure.
When we go diving, we breathe from compressed gas. The largest components of this gas are Oxygen and Nitrogen. When we are under pressure and breathe from the cylinder, these gasses are absorbed into our tissues and bloodstream. Our bodies are able to metabolise the Oxygen. However, Nitrogen, being an inert gas, means we cannot metabolise it, so it gets absorbed and stored into our tissues. As we dive and remain under pressure, we absorb more and more Nitrogen into our tissues, which doesn’t cause a problem as long as we stay at pressure.
However, when the pressure is decreased again (by ascending or surfacing), the Nitrogen that we absorbed, must be released. If the pressure is decreased gradually, the gas is released slowly through breathing, causing no immediate harm, but if the pressure is decreased too fast, the nitrogen will be forced to be released too fast and can form harmful gas bubbles within our tissues.
Imagine a can of fizzy drink: If we shake the can, the pressure inside becomes higher than the atmosphere surrounding it (symbolising us breathing compressed air at depth). Now if we were to open the can immediately it would cause a very fast reduction in pressure (symbolising us ascending/surfacing too fast)– the can will fizz over.
However, if after shaking it, we let it rest for a few minutes before opening it (symbolising our safety stop and slow ascent), the pressure inside will gradually decrease and no fizzing (or very little), will occur.
By controlling our ascent rate and doing a safety stop before surfacing, we allow time for the Nitrogen in our tissues to be released slowly, thus preventing harmful gas bubbles formation.
What are silent bubbles?
No matter how slow the ascent rate and adding our safety stop; because we have breathed gas under pressure, we have still absorbed Nitrogen which, therefore must be released on return to atmospheric pressure. Going slowly and taking our time will simply control the rate of release by producing only very tiny micro gas bubbles. Due to the fact that these bubbles cause no immediate harm, they are known as asymptomatic bubbles or silent bubbles.
Scientific research has been done regarding these silent bubbles by using a Doppler ultrasound, which is a device that allows us to listen to blood vessels. If we were to listen to a Doppler ultrasound on a non-diver, the sound you would hear would be the expected ‘whoosh, whoosh’ as the blood is pumped around the body. However, when listening to the blood vessels of a diver after a dive, we can actually hear the presence of the bubbles as they travel in the blood.
Much research has been done on how long these bubbles stay in our system and this is where dive tables come in. Without going into too much detail, a theoretic calculation has been done to give us general rules and is based on the fact that we have different types of tissues and each type has a different rate of gas absorption and release time.
Why avoid exercise after diving?
Imagine these microbubbles being pumped around in our blood stream, we want to keep our blood pumping nice and gently. Certain activities like exercise, alcohol and cigarettes all increase the rate at which our blood flows. This means those tiny bubbles will be pushed around faster and bump into each other and therefore risk increasing in size. For this reason, it's best to avoid these activities for at least a few hours after a dive.
Being fit and healthy will lower the risk of these bubbles causing harm. Factors such as age and being overweight, as well as diving when tired, dehydrated or fatigued can also increase the risk. Of course, deeper, prolonged dives and rapid ascents should be avoided and of course the golden rule – always listen to your dive computer!
Signs and Symptoms of DCS
- Numbness, tingling and/or paralysis in the limbs
- Pain in the joints
- Dizziness/vertigo
- Skin itch
- Rash
- Confusion
- Shortness of Breath
- Ringing in the ears
- Unusual fatigue
If you suspect DCS, make the diver breathe pure oxygen and give them fluids, call your local Emergency services (preferably where a deco chamber is available) and call DAN ( Divers Alert Network) to speak to a trained diving medic who can advise you and connect you with the best services in your region.
DAN® is the world's leading dive safety association.
DAN Indonesia Emergency Hotline: +62 21 5085 8719.
DAN World hotline· +1-919-684-9111 (accepts collect calls)
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