You would think breathing is the most natural thing in the world. You’ve been doing it all your life without much thought. Inhale, exhale. What could be simpler? Breathing underwater, however, even with a tank of air, requires a little more knowledge than ‘inhale, exhale’.
It’s been known for over a hundred fifty years that simply providing the diver with air to breath isn’t enough to guarantee a safe, healthy diving experience. To explain why, requires a short detour into some ultra-elementary physics. Imagine someone stands in front of you and gives you a little nudge on the chest. Your tendency is to fall backward. But if someone else stands behind you and pushes forward at the same time and with the same force, you remain stationary. You just get a little squeezed between the two forces. Something similar happens when you’re underwater, only the pushing is coming from all sides simultaneously. Except from the inside of your body. There the ‘oppositely directed force’ is provided by the rigidity of your rib cage, muscles and tendons. If it didn’t, your body would collapse under the tremendous pressure which you are exposed to. How much pressure? As you dive, for every 33 feet (10 m) you descend the pressure increases by 1 atm (one atmosphere), or about 14.7 lbs (6.7 kg) per square inch all over your body.
In order to balance that inward pressure, your body has to push outward. But, your ribs and muscles are somewhat flexible. They collapse inward a very short distance before gaining enough rigidity to balance the pressure. That along with other factors compresses your lungs a small amount. As you dive deeper, expanding your lungs becomes more difficult because of the added pressure.
Adding to your difficulty is the fact that air is fairly easy to compress. To compress water requires considerable force. The result is that the air in your lungs compresses somewhat. In order to breath properly, you have to expand the lungs against that small collapse, plus the compression of the air, plus the extra needed to pull in enough air to supply your body with oxygen.
Modern tanks and diving regulators are designed to help overcome these problems. As you dive deeper, the regulator/tank system delivers air always at the ambient pressure of the water. With their use, divers can breathe easily and normally to moderate depths. At great depth other factors come into play.
There are a few ways, skilled divers help their breathing. One important way is by conserving oxygen. The amount of oxygen needed is slightly higher underwater since you are moving around in a dense fluid. That’s one of the reasons divers try to swim in a leisurely way under water… to lower the oxygen needed and conserve what they’ve taken in. Another way is by keeping a cool head. It’s easy to get excited underwater by all the fascinating sights. It’s easy to get stressed when possible dangers lurk in low visibility conditions or when getting tangled on underwater debris. Staying calm helps keep the heart rate low, keeping oxygen demand moderate.
Breathe right and dive safely.