Mary has a checkride tomorrow and hadn’t been able to schedule an air- plane for additional practice until today. But she also had a cold that had hung on for several days. She thought she would be okay because she was feeling better; however, about 45 minutes into her practice, she began to feel a headache over her eyes. It got worse every time she made her approach. Finally, on the ground, the headache got progressively worse until it was bad enough for her to see her doctor. She had a sinus block severe enough that she couldn’t fly for another week, even using decon- gestants. Her doctor shared her frustration because the cold had cleared, but there was still congestion in her sinuses, enough to cause the block on the descents.
The body can withstand tremendous changes in pressure as long as air pres- sure in the body cavities is able to equalize with the ambient air pressure. In other words, the pressure inside any part or organ of the body where gas is present does not generate any problems unless that pressure is not the same as the pressure surrounding that cavity. Problems occur when the expanding (or contracting) gases within the body cannot escape to allow ambient and body pressures to equalize. When gases within body fluids, such as blood, escape from the fluid and enter the body as gases, this also causes prob- lems, often called the bends. The bends will be discussed later in this chapter under the section on decompression sickness.
Review of gas laws
Boyle’s Law needs to be reviewed because it is the basis for virtually all of trapped-gas problems. This law states that the volume of a gas is inversely proportional to the pressure exerted upon it; therefore, as we ascend and the pressure outside the aircraft decreases, the air (which includes water vapor—wet gas) expands. If that air were in a balloon, the balloon would get larger. When considering expanding gases in the body, these gases also have water vapor included, which expands more than dry air.
Dysbarism is a synonym often used for the bends and sometimes associated with trapped gas. This is no longer an accepted term, since it is nonspecific.
It is better to use the terms trapped gas and ear or sinus blocks.
BODY CAVITY AIR POCKETS
There are few closed air pockets such as easily blocked sinuses and middle ears. All other organs, such as the stomach and intestines, abdominal and chest cavities, urine bladder, chest, joints, etc., are either filled with fluids or digesting food and feces or whose walls collapse. Swallowed air from eating too fast or chewing gum, and gases formed by bacteria in the large bowel are the exception.
As a result of a greater differential in pressure per thousand feet at lower alti- tudes, the risk of developing any kind of block is actually higher at the lower altitudes (below 15,000 feet). In other words, a rapid descent from 30,000 feet to 20,000 feet will often cause little or no discomfort where a similar rate of descent from 15,000 feet to 5,000 feet will cause great distress. The greatest pressure change (differential) is from sea level to 5,000 feet. This effect is also noticed in scuba diving, where the most noticeable pressure changes occur in the first 15 to 30 feet.
Review of pertinent anatomy
Those air-filled cavities in the human body most susceptible to trapped gas problems are the sinuses, the middle ear, and occasionally the gastrointesti- nal system. Rarely, dental cavities will be involved. The sinuses are cavities in the bony skull with usually one narrow opening into the nasal passages. The sinuses, including the openings, are lined with moist mucous membranes.
The middle ear is another air filled cavity with only one opening, the eusta- chian tube, with a lining of mucous membranes. The gastrointestinal system is not a common problem location, but because the bowels are potential air-filled cavities, there can be a bloated feeling with passage of air at both ends.
Middle ear block (barotitis)
During ascent, as the ambient air pressure is reduced, the expanding air within the middle ear is intermittently released through the eustachian tube (Fig. 5-7). During descent the same process should take place, but in the opposite direction. This equalization of pressure on either side of the eardrum is essential for proper hearing because the flexibility of the eardrum must not be compromised. As the pressure increases in the middle ear, a small bubble will form that escapes through the eustachian tube after it reaches a certain size. One can often feel this equalization of pressure as the air bubble “pops”
out. This process can also occur during initial ascent.
This pressure equalization should be relatively automatic without any conscious effort, especially under ideal conditions. Normal swallowing usually clears the ears. Problems arise when the eustachian tube does not allow passage of air, usually a result of the mucous membranes being swollen from a cold or hay fever. Furthermore, the nasal end of the eusta- chian tube is narrower. Often, the passage of air is only outward but not back into the middle ear, a form of a one-way valve. This is where prob- lems develop.
An unexpected delayed blockage occurs when breathing oxygen, as in unpressurized cabins at altitudes requiring oxygen breathing masks. Here, pure undiluted oxygen enters the cavity. If a block occurs and it is unable to be cleared, the cavity now is pressurized with oxygen, which, in turn, is absorbed by the mucous membranes. Now, instead of high pressure, a lower pressure develops, with equally disabling symptoms. Another phe- nomenon that is fairly frequent is passengers who sleep through the flight, are not actively clearing their ears (swallowing rate decreases during sleep), Trapped gases 71
72 Altitude physiology
and during descent develop a mild block; however, the real problem occurs a few hours later, after the oxygen has been absorbed in the still-blocked ear. The pain is now worse as a result of the negative pressure in the middle ear.
Symptoms
Inability to clear your ears (equalize pressure) can result in everything from a mild discomfort to severe pain in the middle ear and radiating to the side of the head—a true disabling earache. Anyone who has ever had an ear block never wants to experience it again. It is worse than a severe toothache. The pain becomes worse as the pressure changes with the continuing descent and will not always go away even when you have landed. Sometimes the trapped gas within the middle ear reaches a pressure that is extreme enough that the Figure 5-7
Figure 5-7 Common methods of clearing an ear block will not work if the block is the result of the mucous membranes being swollen from a cold or hay fever.
eardrum ruptures. The good news is that the pain will almost instantly go away but now you have a tear in the eardrum, which needs treatment by a physician. If there is an unequal block in both ears, there can be a disruption of the vestibular system with resulting disorientation.
Whatever the cause of the ear block, you are now impaired, potentially inca- pacitated, or at the very least, distracted from flying duties. The ear can be physically damaged, sometimes permanently. Despite continuing awareness of the causes of ear blocks and the dangers associated, pilots still get into trouble. A major cause of the pilot getting to that point is his delay in recog- nizing that an ear block is developing and failing to begin clearing the ears soon enough.
Treatment and prevention
As with so many things in flying, the best treatment for a medical problem is to prevent it from happening. Every pilot has heard that flying with a cold or congestion is asking for trouble, yet many pilots will fly under these con- ditions. Admittedly, only a few develop a serious block, but that infrequent event is a major risk to safe flight and not worth playing the odds.
In reality, if every pilot grounded himself or herself for every sniffle, there would be few flying; therefore, if you have a mild congestion (and there is no good definition of mild), then taking some decongestant medication before you begin the flight might be appropriate. This medication must not contain antihistamines. Selected long-acting nose sprays might also allow you to fly.
The dilemma is that, technically, no medications are legal or safe if there is any possibility that side effects or the reason for the treatment could compro- mise your performance, Most AMEs should be able to help you decide, but the ultimate decision and responsibility is yours.
If you are prone to early ear blocks, it might be wise to carry a small bottle of long-acting nasal spray in your flight bag. This should be used only when you sense a block developing early enough that the spray has a chance to take effect, but only while all other measures are used in relieving the block. It’s a
“get me down” treatment.
The safest and most common method of clearing an ear block is to move the jaw and swallow at the same time. Chewing gum is a great way to do this, and airlines used to routinely give out gum to passengers just prior to descent for that reason. Yawning, moving your jaw around, or a combination of all will often clear the ear.
Another technique, and probably the most effective, is the Valsalva maneuver.
Again, as soon as you feel a block beginning to develop, hold your nose tight (as if you were going to jump into a swimming pool). Then blow hard against your nose (as if you wanted to blow your nose). This will often increase the pressure within the nasal area and force air back into the middle ear through the eustachian tube. It is not likely (although possible) that you can blow hard enough to injure the eardrum, so it’s okay to blow fairly hard. Don’t wait for symptoms to get bad. Begin early at the first sign of pressure. This is the same procedure that scuba divers always use when descending.
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74 Altitude physiology
If all this fails, consider taking the aircraft (or cabin altitude) higher, to a level above where the block began. Then begin a very slow descent, using the tech- niques already mentioned but now under controlled conditions.
If a block persists after landing, see your doctor. Unresolved blocks can lead to inflammation and sometimes an infection. A middle-ear infection will tem- porarily ground you.
Sinus block (barosinusitis)
Basically, the same events occur with the sinuses, except the openings to the sinus cavities are much smaller and the Valsalva technique is not as effec- tive. The pain from a sinus block is as incapacitating as an ear block, and often more so. It’s said that a sinus block feels like “an ice pick in the fore- head.” All the more reason to be cautious in flying with a cold or hay fever.
Additionally, the sinuses are affected by both ascent and descent, unlike the middle ear.
Teeth (barodontalgia)
Tooth problems are caused by cavities, abscesses, and inadequate fillings (Fig. 5-8). Pain often increases with altitude and can become disabling.
Descent will usually bring some relief. Dental intervention is essential once such a block is recognized. Explain to the dentist what the circumstances are relating to the tooth pain (while flying). If it feels as if the entire top row of teeth is hurting, or if the pain occurs on descent, it is probably a sinus block rather than a tooth problem.
Figure 5-8
Figure 5-8 See your dentist as soon as possible if you experience unusual tooth pain while flying.
Gastrointestinal (GI) tract
The gastrointestinal (GI) tract consists of everything from the mouth to the rectum/anus and includes the stomach and the small and large intestines.
These organs already contain a small but variable amount of gas from swal- lowing and from formation by the digestive process (Fig. 5-9). Remember that ambient air also includes water vapor, and within the body that amount and subsequent partial pressure increases. The pain, which is similar to the cramps felt when constipated, can be quite severe. The symptoms vary from pain to a mild discomfort in some individuals, with reluctance to allow equal- ization through belching or passing flatus.
Prevention
It is common knowledge that certain foods can produce gas (flatus). Beans are the most common, and other foods include cabbage, onions, raw apples, radishes, cucumbers, and some melons. Fluids are very important to ingest in flight to prevent dehydration, but carbonated beverages will increase the gas in the gastrointestinal tract. Gum chewers also swallow a lot of air. A pilot who develops gastrointestinal gas as a result of any of the above cannot be modest. Getting rid of the pressure by allowing the gas to escape at either end of the gastrointestinal tract will help relieve the discomfort. Failure to do so could be more embarrassing. As the old saying goes, it’s better to burp and bear the shame than not to burp and bear the pain.