and so too does the pressure of air. Many different factors affect the density of air. Most measurably, as altitude increases, air becomes less dense, decreasing atmospheric pressure. Standard ...

In addition, for reasons not entirely understood, high altitude and lower air pressure causes fluid to leak from the capillaries which can cause fluid build-up in both the lungs and the brain.

And running at high altitude can carry its own particular risks. At high altitudes the percentage of oxygen is just as high but there’s not as much pressure, so you have to work harder getting air ...

To maintain the pressure in the cabin equal to that at low altitude, even while the airplane is at 30,000 feet, the incoming air is held within the cabin by opening and closing an outflow valve ...