What every scuba diver needs to know about the ‘bends’

June 3, 2008

We have reported recently on far too many accidents happening to scuba divers and although many accidents are not related to the ‘bends’ here is some useful information about the most common of ailments to affect divers.

There’s probably no diving disease more well know or more feared than decompression sickness, better known by its nickname “the bends” which came about because affected divers would often bend over in pain, the bending was said to relieve some of the pain.

But what causes the bends?
What’s the physiology behind it and how do you prevent it?

Here’s a quick look at diving’s most famous ailment.

The villain in our story is nitrogen: as we sit on the surface we’re breathing air that has about 79% nitrogen. We can convert this number into a pressure of 0.79 atmospheres.

Because we breathe this amount of nitrogen all the time, our bodies are saturated with 0.79 atmospheres of nitrogen. Now let’s say we go down to 66 feet (20m) saltwater. We are now under 3 atmospheres of pressure and the air in our lungs is more dense. We’re currently breathing 2.37 atmospheres of nitrogen (0.79 x 3= 2.37) but our bodies are still saturated with only 0.79 atmosphere of nitrogen. Since our bodies will seek equilibrium with the environment, we’ll begin to absorb nitrogen until our bodies become saturated with 2.37 atmospheres.

This diffusion happens first in the lungs. The higher partial pressure of nitrogen in your lungs diffuses into your bloodstream. Then the nitrogen diffuses into the denser tissue of your muscles and finally into your bones. As long as you maintain a pressure of 2.37 atmospheres, there’s no problem.

But, you can’t stay underwater forever; you have to surface eventually and that’s where things get a bit tricky.

What happens to the nitrogen as you ascend?

As you surface, the pressure of nitrogen in your lungs decreases so the nitrogen in your body tries to decrease to match. The nitrogen will try to leave your body tissues into your blood and then from your blood, the nitrogen will circulate to the lungs where it can be expelled.

The problem is that this process takes time and the more nitrogen you have in your system, the slower you have to ascend to allow your body to get rid of all that nitrogen.

It may help to think of your body like a bottle of soda. Imagine a bottle of soda sitting on the counter at the store. You look at the bottle and it doesn’t look like there are any bubbles in the soda at all. In fact, if you open the bottle slow enough there’s a chance that no bubbles will form. However, if you crank the soda bottle open and instantly release all that pressure, all the CO2 will leave the solution and come bubbling to the surface.

Your body is a lot like that. Give it enough time and release the pressure slowly and you’re okay. But if you release all that pressure quickly, the nitrogen gas will come rushing out of your blood in the form of thousands of little, deadly bubbles and here come the scuba diving bends.

Like most potential diving diseases, scuba diving bends, prevention is a lot better than the cure. Make sure you plan your dives carefully and allow yourself a reasonably long surface interval. By using the responsible diving practices you learned in your basic diving course, you can make sure that you never have to experience scuba diving bends first hand.

My thanks go out to The Underwater Diving Equipment team for this great information.



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