how airplane contains air pressure
Although aircraft cabins are pressurized, cabin air pressure at cruising altitude is lower than air pressure at sea level. At typical cruising altitudes in the range 11 000â12 200 m (36 000â40 000 feet), air pressure in the cabin is equivalent to the outside air pressure at 1800â2400 m (6000â8000 feet) above sea level. As a consequence, less oxygen is taken up by the blood (hypoxia) and gases within the body expand.