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Trapped Gas: Problems Of High-Altitude Flight

Donald Anders Talleur


When you hear the phrase “trapped gas” several different images (and maybe even smells) come to mind. But while the topic might be a joking matter on the ground, it may indeed be no joking matter while aloft, especially if you’re the one suffering from the affliction.

And trapped gas is not limited to hiding in the intestines; it can be found in the ears, sinuses, teeth, and also manifest itself in the joints as a result of nitrogen accumulation in low pressure environments.

In discussion, the problem of trapped gas is separated into two distinct categories: Barotrauma, and Decompression Sickness (DCS). This month I’ll tackle the topic of Barotrauma during flight.

Barotrauma is a fancy term that refers to pain or other injurious symptoms as a result of trapped gas in body cavities. Simply put, the body has a multitude of cavities where gas can accumulate. As mentioned be fore, these include the ears, sinuses, GI tract, teeth, but also include less common areas of the body; I’ll focus on the first four.

When considering the problems of trapped gas, both the ears and sinuses are closely related in that both are likely to get “plugged” up when the pilot is suffering from any sort of upper respiratory congestion (e.g. allergies, head cold, etc.).

In the case of the ears, the inner ear vents during climb normally, and automatically, by equalizing the higher inner ear pressure with the lower ambient pressure outside.It accomplishes this by allowing air to pass through a small tube (Eustachian tube) that vents to the upper back of the mouth cavity.

On descent, the soft area of the tube collapses, and so the pilot needs to move the jaw, valsalva, or perform some other type of movement that will allow the tube to flex just enough to allow air back into the inner ear.

To understand how this works, 1) take a balloon and cut off a small area from the closed end so that the balloon is now open at both ends, 2) now blow through the normal end; air will flow freely as you blow. This demonstrates how the Eustachian tube responds during climb.3) Now try to suck air through the normal end. The balloon collapses, making it difficult to pass any air through the “tube.” This represents normal function of the Eustachian tube during descent.

Under normal circumstances, minor flexing of the jaw will allow the equalization of pressure to take place. However, when congested, the Eustachian tube opening may be swollen so that pressure does not equalize so easily. Failure to correct the condition will result in inner ear pain, which of course may serve as a severe distraction to the pilot.

The valsalva manoeuvre, chewing gum, yawning, wiggling the jaw, and coughing against pressure are all useful ways to clear the ears.

Barosinusitis, or sinus block, is also a potentially serious problem in that the facial and forehead pain from a sinus block can be excruciating. There are four sets of sinus cavities in the skull, the frontal, ethmoid, maxillary, and sphenoid. While the names are not of critical importance, what is important is that sinus swelling or pressure impacts nerves and can lead to headaches or even the temporary loss of an eye due to pain and watering.

When working normally, the sinuses leak a small amount of mucus into the nasal cavity, serving the dual purpose of moisturizing the incoming air, and acting as a sort of sticky filter that catches dust and other contaminants.A blockage means that the sinuses will not drain properly, nor will air pressure equalize during climbs and descents. In general, if sinus pressure is experienced during climb, do not climb any further.

If it’s experienced during descent, level off or climb and then resume a slower descent with the valsalva manoeuvre. If pain becomes too much to tolerate, sometimes use of a nasal decongestant (like Afrin) is helpful. Of course, the #1 way to avoid sinus blockage pain during flight is to avoid flying while congested.

Another nasty sounding barotrauma is called barodontolgia, or a sudden sharp tooth pain that occurs in response to changes in atmospheric pressure. This type of pain generally occurs on ascent and most often affects diseased teeth (another good reason to have good dental hygiene).

It is however possible that restored teeth may also be susceptible.While the exact mechanism for in flight toothache is not fully understood, (low pressure experiments have failed to reproduce pain) it is accepted that completely normal teeth are not affected by this problem.

Also, it differs from the referred pain of barosinusitis in that tooth pain is relieved by descent.

The majority of reports indicate that onset of pain is commonly between 5,000 to 15,000 feet and that the altitude of onset is remarkably constant for a given pilot. The severity of the pain does not necessarily change if ascent is continued, but there is not a good way to judge that ahead of time. The best course of action in the event of tooth pain is to level off and/or descend.

Gas in the gastrointestinal (GI) tract is the most common of all trapped gas problems, and is usually the easiest to alleviate by, you guessed it, farting. As embarrassing as it might be to pass gas in the presence of others, there are few situations where it is more important than during flight.

The problem is that there is always a certain amount of gas in the stomach and intestines.This is normal. But as the atmospheric pressure decreases during climb, that intestinal gas increases in volume.

Obvious problems crop up, like feeling of fullness in the lower stomach, abdominal pressure, and even mild to severe cramping during climb. While this condition is rarely life threatening, it can become a distraction if an attempt is made to “hold it in.”

I should also point out at this juncture, that holding it in too long sometimes leads to slightly more than anticipated once “venting” finally takes place. So passing gas and belching are important to the relief of GI trapped gas.

Moving around and/or massaging the abdomen may also be helpful in alleviating cramps associated with gas.

Perhaps the best solution to abnormal amounts of GI gas problems during flight is to have a careful diet prior to flight. The list of “danger” foods is long and unfortunately includes a whole slew of foods that are also some of the healthiest to eat. That said, high fibre foods can cause problems, especially if the diet doesn’t normally include them.

Beans are cited as a culprit by most people so it might be wise to avoid large portions of those within a few hours prior to flight.

The bottom line on gassy foods is that each person is different.Each of us has a good idea of what causes gas and what doesn’t. If you plan to fly, especially at higher unpressurized altitudes, think before you eat!

So for this months topic, eliminating or alleviating trapped gas problems is a function of 1) not flying with upper respiratory congestion, 2) using caution about higher altitude with diseased or recently restored teeth, and 3) eating carefully prior to flight. If you can’t do those things, then know how to do the valsalva manoeuvre, carrying a bottle of Afrin, limit your altitude to below 5,000 feet MSL, and plan to pass gas frequently during the flight!

This month’s Pilot’s Primer is written by Donald Anders Talleur, an Assistant Chief Flight Instructor and Researcher at the University of Illinois, Institute of Aviation. He has been flying since 1984 and in addition to flight instructing since 1990, has worked on numerous research contracts for the FAA, Air Force, Navy, NASA, and Army. He has authored or co-authored over 200 aviation related papers and articles and has an M.S. degree in Engineering Psychology, specializing in Aviation Human Factors.