 With the invention of the hot air balloon that made it possible to have the first human flights it became evident that exposure to altitude caused some physiological changes in the body. Some of these changes occur inside the natural cavities in the human body that contain varying amounts of gas, namely the middle ear, sinuses, stomach, and intestines. The gases within the body are governed by physical and chemical laws that describe how a volume of gas changes in response to changes in pressure and temperature. These body cavities each have openings that allow gases to enter or exit. Problems arise when these openings are reduced in size or closed. The gas then is considered trapped and can cause problems. Do you remember the law that explains the effect of pressure on these areas? It's Boyle's law. Boyle's law states that a volume of gas is inversely proportional to the pressure to which it is subjected with the temperature remaining constant. You can see this law in action by observing a balloon taken to altitude in an altitude chamber. As the pressure decreases around the balloon, the volume within the balloon will expand. As the chamber is descending, the pressure increases around the balloon. The volume within the balloon will decrease. During the ascending phase of a flight, you are more likely to develop problems in the gastrointestinal tract. In rare occasions, teeth may be the source of gas expansion problems. As you ascend, gas expands in the stomach and the intestines. This can cause abdominal pain and in severe cases may even cause fainting. The human body has two avenues that allow gas to escape, burping and flatulating, commonly referred to as passing gas. Pilots should watch their diet and avoid foods that cause excess gas formation. Additionally, avoiding carbonated beverages or large amounts of water from a fountain prior to flight will help minimize these problems. Carbonated drinks are bottled under pressure, contain large amounts of carbon dioxide, which in itself is not harmful, but the gas does expand as we go to altitude. Individuals tend to swallow large amounts of air when drinking from a fountain. Drink from a cup, glass, or bottle if available. Avoid chewing gum during ascent because air is swallowed during the chewing process. As a pilot, if you encounter any abdominal pain on ascent, you should do the following. Treat as soon as the symptom appears. Relieve internal pressure by belching or passing gas. Massage affected area. If problems continue, descend. With advances in modern dentistry, problems with trapped gas in the teeth are rare. To diagnose a problem with a tooth, descent can be made until the pain ceases and then re-ascend. The tooth pain may re-occur at the same altitude at which the pain was experienced the first time. Dental problems that can cause pain on ascent include a cavity or bad dental work, loose filling, where air is trapped inside the tooth and cannot escape, an abscess located in the gum next to the root or inside the root of a tooth, a swollen maxillary sinus that usually results from an impacted wisdom tooth. The treatment for a tooth problem is to descend and see your dentist as soon as practical. Maintaining a schedule of good dental hygiene and regular checkups will help prevent future problems. During the descending phase of flight, you are more likely to develop problems in the middle ear and the sinuses. This illustration shows the anatomy of the ear. As pilots ascend, the ambient pressure decreases, expanding air within the middle ear. That air is intermittently released to the environment through the eustachian tube. The eustachian tube connects the middle ear with the back of the throat. During descent, as the ambient pressure increases, air forcibly reenters the middle ear through the eustachian tube. This equalization process is accomplished simply by swallowing or using an exaggerated jaw movement. However, if the person has an upper respiratory infection, like a cold with nasal congestion, the eustachian tube may be blocked due to local swelling. Although the middle ear may allow the escape of expanding gas on ascent, it is unlikely that it will allow the reentering of air during the descent. Consequently, an air pressure differential develops between the middle ear and the environment that will cause the eardrum to retract. Depending upon the magnitude of this air pressure differential, the person may progressively experience problems that extend from a sensation of fullness, minor hearing loss, discomfort, ringing in the ears, pain, dizziness, nausea, to eardrum rupture. There are several ways to relieve this internal pressure. You can do so by yawning, swallowing, chewing, performing a valsalpha, which means holding your nose and mouth shut while trying to exhale forcefully through the nose. If there is no relief after trying these options, it may be best to climb back up a few thousand feet to try to relieve the pressure. Then a more gradual descent should be used, performing the previous methods of relieving the pressure. A pilot may need to stair step down from altitude. A similar trapped gas problem can be experienced when an individual sinuses cannot equalize the air pressure changes due to sinus duct blockage, commonly caused by colds or allergies. This illustration shows the anatomy of the sinuses. The most commonly affected sinuses are the frontals and maxillaries. They can cause trouble on both ascent and descent. However, you are more likely to experience difficulties on descent. The valsalpha maneuver is one effective method in providing relief for sinus blockage. A sensation of fullness may or may not appear before the onset of sudden pain. Sinus block pain feels like an ice pick in the face. An important possibility is that the onset rate of a sinus block pain can occur faster than middle ear problems and can become incapacitating, giving the air crew little time for decision making. The key to prevention of middle ear and sinus problems is to never fly with a cold or when sinuses are full due to allergies, or when on medication for upper respiratory problems. Remember, if you have to self-medicate to fly, you're not at your best, and that could jeopardize the safety of your flight. The four areas of the body where trapped gas can occur are the middle ear, sinuses, stomach, and intestines. The gases within the body are governed by physical and chemical laws that describe how a volume of gas changes in response to changes in pressure and temperature. These body cavities each have openings that allow gases to enter or exit. As you ascend, gas expands in the stomach and the intestines. Therefore, pilots should watch their diet and avoid foods that cause excess gas formation. Problems with trapped gas in the teeth are rare. A schedule of good dental hygiene and regular checkups will help prevent teeth problems. During the descending phase of flight, you are more likely to develop problems in the middle ear and the sinuses. The key to prevention of middle ear and sinus problems is never to fly with a cold or when sinuses are full due to allergies or when on medication for upper respiratory problems. If you have to self-medicate to fly, you're not at your best.