When you are traveling at 37,000 feet, a lot of things are different – medical issues included.

Aviation medicine actually rates as a sub-specialty these days under the Preventive Medicine Board.

There is a whole physiology of flying, changes in pressure and oxygen that the body needs to adapt to. There’s much more going on than simply picking a drink to sip on, while going the better part of 500 miles per hour.

What’s different about flying?

Pressure for one thing. Here at sea level, we have a couple of miles of air on top of us. The weight of this air puts 15 pounds per square inch of pressure on us. Go up in a plane and there is less pressure, like coming to the surface from the deep end.

You can’t compress a fluid, so most of your body is at peace with the pressure changes. But air spaces do compress, and we have some behind our eardrums, the sinuses, and bubbles in the stomach/intestines.

As the airplane climbs, the pressure lessens. High pressure air in your ear bulges the eardrum out, until it is vented out through the Eustachian tube. After a few hours at altitude, your ear is filled with low pressure air.

On descent, the pressure increases as you dive deeper into the atmosphere. The eardrum gets pushed inward, until higher pressure air is vented in through the Eustachian tube. It is critical that the vent tube is clear or the eardrum will blow out, or blow in. Head congestion, from a cold or allergies will cause swelling in the Eustachian tube, often blocking it.

The same thing happens in the sinuses if a sinus gets blocked. The pressure builds until you think your face will explode – very painful. Keep the head passageways clear before you fly. A good decongestant, or Afrin nasal spray, an hour before you fly, often helps.

The air is thin at 37,000 feet, too thin to breathe.

To keep the passengers conscious enough to choose peanuts or pretzels – and the pilots to fly the plane – the cabin is pressurized. To pressurize an airplane they have airtight doors and windows. Then they pump in the thin air and build up the pressure until the air is as thick as it is at 8,000 feet (25% less oxygen).

There is a handy source for compressed air. Huge multistage compressors make jet engines work, so high pressure air is bled from the jet engine into the cabin. (For the record, they take this jet engine air from the part of the jet engine that isn’t on fire.)

The very air you breathe in a jetliner is a computer controlled, High-Efficiency Particulate Air (HEPA) filtered mixture of outside and recirculated air designed for passenger comfort and fuel efficiency. Since the air coming off the jet compressor is hot (almost 500 degrees) no live germs survive the passage.

As air is recirculated in the cabin, it is HEPA filtered, which removes germs coughed up by passengers. This won’t protect you from the guy with the sniffles sitting next to you, but at least you won’t be breathing everybody else’s germs on the plane.

The air is also very dry, generally just 10 percent to 20 percent humidity, which prompts some people to reach for their Chapstick.

Personal space, or lack of it, is also an issue in commercial air travel. I haven’t felt so packed together since high school basketball games. Airplanes are definitely not the place for someone with claustrophobia, and a bit unnerving for the rest of us.

All that sitting still, with your legs hanging down, slows down the circulation in your legs.

Your feet swell and, in rare instances, the blood in your leg veins clots. This is more likely if you are prone to blood clots, from smoking or birth control pills.

Blood clots in your legs can break free and cause havoc on your heart and lungs.

Avoiding blood clots is fairly easy – get up and move around pretty regularly, maybe every 20 minutes of so. An aspirin before flight also will make the blood less sticky.

Another issue on airplanes is air sickness, a variant on car-sickness or boat sickness – basically motion sickness plus some anxiety.

Conflicting signals from your eyes and inner ear can give you a memorable case of nausea. That is something that is much easier to prevent than to treat.

Bonine (meclizine) is available over the counter and very effective in preventing motion sickness by taking one an hour before getting on the plane.

A consequence of air travel – jet lag – is when your body thinks it’s midnight when it’s only 8 p.m., or the opposite. Your body expects bed and meal times to be sensibly spaced from when you awoke.

Going to bed much less than 16 hours from wake up time, or much more, is tough to do. You can waste the first half your precious vacation as a sleep deprived zombie. Getting home jet lagged, and trying to do all the backed-up work, is also interesting. There are no easy answers to for this. Medications from melatonin to Viagra have been used, as well as a 16-hour fast to reset the inner clock. Try to gradually adjust bed and wake up times a few days before your trip.

Finally, don’t forget about the boredom of long flights – bring a good book or your iPad to fight that ailment.

Some good preparation will go a long way toward making your next crowded flight a bit better.

Have a good trip,

Dr B.

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