UPR.B | Airborne and Feeling It

Grab your chewing gum and get ready to yawn, because we’re going to talk about pressure!

If you’ve ever flown in a plane, you’re familiar with the effects of pressure, but you probably didn’t give it much thought.  After a minute into the climb your ears start to feel funny and someone probably told you to yawn or chew some gum.

But have you ever wondered why?  What’s going on inside and outside the plane that causes your ears to do that?

Air Pressure

If you didn’t already know, the air pressure is different at different altitudes, starting at sea level and going all the way up to space.  Humans are, in general, pretty well suited to life on the ground around sea level; that doesn’t mean on or near the sea, it basically just means the lowest area on the surface of the planet.  Some places on earth, like Death Valley in California, or Lake Eyre in Australia are in low points that are below sea level, but that’s not important right now. What is important is that as you move up in altitude, the air starts to get “thinner,” which means that there is less pressure and less oxygen in the air.

But first, in order to understand how pressure works, you have to understand how breathing works.  Breathing is something that we seldom, if ever, think about. In fact, you don’t have to think about it at all!  While you can control it – everyone hold your breath for a few seconds – see? But before you did that – oh, sorry, exhale – before you had to think about inhaling and holding that breath or when you would release it, you probably didn’t give any thought to the fact that you were breathing at all.

But what is happening while you’re breathing, whether or not you’re thinking about it?

Just before you inhale, the air pressure inside your lungs is equal to the pressure outside your body, whatever that pressure level is.  When you inhale, your muscles work to draw in air and expand your lungs to increase their volume. When you do this, the pressure in your lungs lowers because of the increase in space inside.  When this happens, the outside air rushes in to fill that space, and then the blood vessels in your lungs can absorb the oxygen that your body needs to survive. When you inhale, you can’t compress any more air into your lungs than the outside pressure.

Think of it this way: have you ever pushed an empty bowl into a sink full of water?

If you push the bowl down into the water – pretend that’s you inhaling – once the bowl breaks the surface of the water, water will begin to rush in until the bowl is full, but it’s not like the bowl can fill with more water than there is in the sink.  The same thing happens with your lungs and the air outside – you can’t pull in more than there is.  What you can do, however, is increase the volume of your lungs by taking deeper breaths.

So what does that have to do with hiking, flying in planes, or going to Denver, Colorado?  Well, as the air pressure around you decreases, so does the amount of air that can fill your lungs.  As I mentioned earlier, humans are best suited to living right about at sea level – that’s the baseline we use to describe what the air pressure is.  At sea level, you’re at one atmosphere; if you dive under water, you start increasing the pressure. When we’re outside the Hab at sixty-five feet (that’s ten fathoms if you’re into old timey measurements), we’re at a little more than two atmospheres, which means that the pressure outside your body is twice what you would experience on the surface.  Obviously you can’t take a big breath of air underwater when you’re just swimming around, but you can bring your own air with you in the form of compressed gasses like oxygen or even helium depending on the depth at which you’re diving.

 And yes, it sounds hilarious to hear a tough old diver talking like Mickey Mouse! Have you ever been on a plane or high in the mountains where your ears ‘popped’? What did you do to solve the problem?