Inside our heads, each of our sinus cavities "communicates" with - has an opening to - the nose. This opening, however, is quite small and may be only one millimeter across. Under normal circumstances, this opening is large enough to let air travel freely between its sinus and the lining of the nose. As we gain altitude, the air pressure around us drops so, relatively speaking, the pressure inside our sinuses is higher than outside. The sinuses don't expand like a balloon because air flows through the communicating channel to the nose, thus equalizing the pressure. The reverse happens on descent.
But if we have a cold or other upper respiratory infection, the mucous membranes that line the inside of all our airways, swell and become inflamed. When this happens, the tiny communicating channels can easily become blocked. Then, pressure in the sinuses may be great enough to force air out through a narrowed channel, taking bubbling bits of mucous with it. That causes the squeaking sound we hear as the pressure equalizes.
This swelling and inflammation acts like a flapper valve. It lets air out, but it doesn't let air back in. That's why we find ourselves in trouble when we want to come down. Our communicating channels are blocked and simply won't allow air to pass back into the sinus and equalize the pressure.
When the pressure outside your head is greater than the pressure in it, you feels like somebody has run a hot knife into your cheek. The pain can be excruciating, and I know of several accidents that have happened because of this. The pressure differential - increasing ambient pressure causing low pressure in the sinuses - can be so great that the sinus lining literally can be ripped right off the bone. This is extremely distracting, and a pilot might not be able to fly his aircraft.
We humans also have an air space where the eardrum separates the outer ear canal from the middle ear. The ear drum is a membrane only one centimeter across, composed of only three layers of cells. It is so thin, I can see through it when I examine a pilot's ear.
For the eardrum to vibrate properly, air pressure on both sides has to be equal. The Eustachian tube connects the middle ear to the back of our throat. Like the sinus communicating channels, the Eustachian tube is very small. It is normally collapsed and held closed by a small muscle in the back of the throat.
As we gain altitude, air can spontaneously bubble out of the middle ear. The small muscle in the back of the throat acts like a flutter valve. During descent, we must actively bring the muscle into play to hold our Eustachian tubes open, which allows air to pass through them and equalize the pressure in our middle ears. If we can't do this, the outside pressure can push the eardrum inward enough that it might rupture.
In general, if you can't equalize or relieve the pressure in your middle ears, the pressure associated with a 5,000-foot altitude change will rupture the eardrum. That will relieve you of your pain - and your hearing. A ruptured eardrum isn't a catastrophe. In most cases it will heal on its own in two to three weeks.
As with your sinuses, a little respiratory infection can cause enough swelling to shut your Eustachian tubes and prevent you from equalizing your middle ears, possibly trapping you at altitude.
To open your Eustachian tubes under normal circumstances, use the Valsalva maneuver. Pinch your nose shut, close your mouth, and try to exhale gently through your nose. This forces pressure into both ears. You should feel your eardrums pop.
I prefer an alternative method because it is considerably more gentle on the eardrum. It's called the "Frenzel" or "jaw-thrust" technique. You simply move your jaw as far forward as you can. Sometimes you need to swallow as well. This also opens the Eustachian tubes and allows you to equalize the pressure in your middle ear.
Pilots who have chronic seasonal or perennial rhinitis (allergic inflammation of the nose's mucus membranes) may be fully certified by the FAA once their symptoms are safely controlled. This requires a pilot to tell the FAA and his aviation medical examiner what the condition is and what treatment is being used to control it. If he (or she) has no serious side effects or sedation, the FAA will probably issue the pilot a waiver.
All pilots should know how to clear their ears properly in flight. However, if you have a cold, it may be impossible. I often carry a bottle of nasal spray decongestant as a "get-me-down" safety measure for passengers to use.
For people with chronic allergies or infections, the inflammation of the nose and airway may be enough to cause a great deal of difficulty, even during the most routine flying. You can prepare your passengers by having them take a nasal decongestant, either a spray or an oral drug. When you are piloting an aircraft, you should never use these remedies. Using a decongestant that contains antihistamines can be a deadly combination with hypoxia from altitude because the resulting fatigue will reduce your ability to make good, safe decisions.
If you need to take a cold medicine to prepare your nose to fly, your head should know better. It's a good day to drive instead. Don't fly with a cold.
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