Although most of the human body is comprised of in-compressible liquid, there are some air spaces that need to be equalized when we go scuba diving.
As divers descend, the air filled cavities will be subject to pressure changes of the surrounding water which can produce pain and discomfort - commonly known as a squeeze - if equalization is ignored.
To avoid discomfort, you keep the air volume of an air space normal by adding extra air to it during descent, keeping the pressure inside the air space the same as the surrounding water pressure.
This technique is Equalization and scuba divers use several different methods to equalize the ears, the sinuses, the lungs, the diving mask and a dry suit.
There are three main methods to equalize your ears and sinuses when descending. They include the Valsalva Maneuver, the Frenzel Maneuver and Swallowing while wiggling the jaw from side to side.
The most common is the Valsalva method which involves pinching the nose closed and then gently blowing against it. This tends to direct air from your throat into your ears and sinus air spaces.
You should equalize every few feet before you feel discomfort and the first five to ten meters tends to need equalizing the most often.
Toynbee maneuver
Lungs are large and flexible and not very prone to a squeeze. Breathing continuously from the scuba equipment equalizes the air space inside the lungs, which is also another reason not to hold your breath while scuba diving.
Equalizing a scuba mask is important as you descend deeper because the increasing water pressure tends to squeeze the mask against your face.
The simple technique to balance this pressure is to add air inside the mask by blowing through your nose. A face mask squeeze is rare but looks extremely painful as it usually results in 'Panda' style bruised eyes.
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