The following are examples of pressure change when you are scuba diving.
As you descend, the volume of gas inside your mask is decreasing due to increasing pressure. Add gas to the mask to make the volume consistent by blowing out enough gas to equalize through your nose.
As you descend, you add gas to the BCD to control your descent. Your exposure suit has gas in it either in the material (neoprene—in the form of bubbles for a wetsuit) or in the suit itself for a dry suit. The gas in the exposure suit will compress making you more negative. You will master how to deal with this and achieve neutral buoyancy using your BCD in your confined water session.
The opposite happens due to the decreasing pressure on your ascent. Your exposure suit and BCD will both have expanding gas, and you will need to vent it from the BCD to control your ascent. It is important that you should never ascend faster then 9 meters/30 feet per min. Why slow ascent rates are important will be explained in detail in the “Physiology” unit.
Ear equalization is affected on your descent. Volume of gas spaces in the middle ear will reduce, and this needs to be equalized just like when you fly in an aircraft and feel the pressure in your ears. This will be explained in the “Physiology” unit.
As previously explained, lungs need to be equalized by continuous breathing, or you can possibly cause injury. Remember to never hold your breath while scuba diving and continuously breath.