It's like in the airplane, but reverse. In ascent, the air volume can naturally squeeze out. On descent however the air won't normally squeeze in easily. I can

It's like in the airplane, but reverse. In ascent, the air volume can naturally squeeze out. On descent however the air won't normally squeeze in easily. I can open my eustachean tubes voluntarily with a yawning-like maneuver. Otherwise you have to pinch your nose and force the air either with your tongue and throat, or lungs.