gases and the body

A.  ozone sickness

Another problem associated with flight at very high altitudes is ozone sickness. Although it has been evident only with flights operating at altitudes of 30,000 feet or more, the advent of general aviation airplanes that operate at subsonic speeds at such levels makes this a problem of which even the private pilot should be aware.

Ozone is a bluish gas that exists in relatively high concentrations in the upper levels of the atmosphere, especially in the tropopause. Because the tropopause fluctuates in its average altitude from season to season, any flight operating above 35,000 feet is likely to come into, contact with ozone at some time.

Although ozone does have a distinctive colour and odour, passengers and flight crew who have experienced ozone sickness have been unaware of the apparently high concentrations of ozone prior to the onset of the symptoms.

The symptoms of ozone sickness are hacking cough, poor night vision, shortness of breath, headache, burning eyes, mouth and nose, mild chest pains, leg cramps, fatigue, drowsiness, nose bleed, nausea and vomiting. The symptoms become more severe with continued exposure and with physical activity but do diminish rapidly when the airplane descends below 30,000 feet.

Some relief from the symptoms can be achieved by breathing through a warm, moist towel. Limiting physical activity to a minimum and breathing pure oxygen are also effective in alleviating the symptoms. 

B.  carbon monoxide

Oxygen is transported throughout the body by combining with the haemoglobin in the blood. However, this vital transportation agent, haemoglobin, has more than 200 times the affinity for carbon monoxide that it has for oxygen. Therefore, even the smallest amounts; of carbon monoxide can seriously interfere with the distribution of oxygen and produce a type of hypoxia, known as anernic hypoxia..

Carbon monoxide is colourless, odourless and tasteless. It is a product of fuel combustion and is found in varying amounts in the exhaust from airplane engines. A defect, crack or hole in the cabin heating system may allow this gas to enter the cockpit of the airplane.

Susceptibility to carbon monoxide increases with altitude. At higher altitudes, the body has difficulty getting enough oxygen because of decreased pressure. The additional problem of carbon monoxide could make the situation critical.

Early symptoms of CO poisoning are feelings of sluggishness and warmness. Intense headache, throbbing in the temples, ringing in the ears, dizziness and dimming of vision follow as exposure increases. Eventually vomiting, convulsions, coma and death result.

Although CO poisoning is a type of hypoxia, it is unlike altitude hypoxia in that it is not immediately remedied by the use of oxygen or by descent to lower altitudes.

If a pilot notices exhaust fumes or experiences any of the symptoms associated with CO poisoning, he should shut off the cabin heater, open a fresh air source immediately, avoid smoking, use 100% oxygen if it is available and land at the first opportunity and ensure that ail effects of CO are gone before continuing the flight. It may take several days to rid the body of carbon monoxide. In some cases, it may be wise to consult a doctor. 

C.  cigarettes

Cigarette smoke contains a minute amount of carbon monoxide. It has been estimated that a heavy smoker will lower his ceiling by more than 4000 feet. Just 3 cigarettes smoked at sea level will raise the physiological altitude to 8000 feet. Because the carbon monoxide in the cigarette smoke is absorbed by the haemoglobin, its oxygen absorbing qualities are reduced to about the same degree as they would be reduced by the decrease in atmospheric pressure at 8000 feet ASL.

The carbon monoxide from cigarettes has detrimental effects not only on the smoker but on the non-smoker as well. After prolonged exposure to, an increased level of carbon monoxide such as that produced within a confined area such as a cockpit by people smoking, symptoms such as respiratory discomfort, headaches, eye irritation can affect the non-smoker.

Cigarette smoking has also been declared as hazardous to health, contributing to hypertension and chronic lung disorders such as bronchitis and emphysema. It has been linked to lung cancer and coronary heart disease. 

D.  hyperventilation

Hyperventilation, or over-breathing, is an increase in respiration that upsets; the natural balance of oxygen and carbon dioxide in the system, usually as a result of emotional tension or anxiety. Under conditions of emotional stress, fright or pain, a person may unconsciously increase his rate of breathing, thus expelling more carbon dioxide than is being produced by muscular activity. The result is a deficiency of carbon dioxide in the blood.

The most common symptoms are dizziness, tingling of the toes and fingers, hot and cold sensations, nausea and sleepiness. Unconsciousness may result if the breathing rate is not corrected.

The remedy for hyperventilation is a conscious effort to slow down the rate of breathing and to hold the breath intermittently, to allow the carbon dioxide to build up to a normal level. Sometimes, the proper balance of carbon dioxide can be more quickly restored by breathing into a paper bag, that is, by re-breathing the expelled carbon dioxide.

Hyperventilation is sometimes associated with hypoxia. A pilot, f lying at high altitude, may think that he can counteract the effects of hypoxia by taking more rapid breaths. Hyperventilation does not help you get more oxygen. It only increases the emission of carbon dioxide.

E.  decompression sickness

trapped gases

During and descent, gases trapped in certain body cavities expand or contract. The inability to pass this gas may cause abdominal pain, toothache or pain in ears or sinuses.

Ear Block

The ear is composed of three sections. The outer ear is the auditory canal and ends at the eardrum. The middle ear is a cavity surrounded by bones of the skull and is filled with air. The Eustachian tube connects the middle ear to the throat. The inner ear is used for hearing and certain equilibrium senses.

As one ascends or descends, air must escape or be replenished through the Eustachian tube to equalize the pressure in the middle ear cavity with that of the atmosphere. If air is trapped in the middle ear, the eardrum stretches to absorb the higher pressure. The result is pain and sometimes temporary deafness.

During climbs, there is little problem since excess air escapes through the tube easily. However, during descents, when pressure in the middle ear must be increased. The Eustachian tubes do not open readily. The pilot and his passengers must consciously make an effort to swallow or yawn to stimulate the muscular action of the tubes. Sometimes it is advisable to use the valsalva technique, that is, to close the mouth, hold the nose and blow gently. This action forces air up the Eustachian tubes. Children may suffer severe pain because of ear blocks during descents. They should be repeatedly reminded to swallow or yawn. Small babies are incapable of voluntarily adjusting the pressure in the middle ear and should be given a bottle to suck during descents.

Painful ear block generally occurs; as a result of too rapid descent. If the pilot or his passengers are unable to relieve the pain of ear block by the methods described, it may be necessary to climb to altitude again and make the descent more gradually.

After a flight in which 100 per cent oxygen has been used, the valsalva procedure should be used several times to ventilate the middle ear and thus reduce the possibility of pain occurring later in the day.

Sinus Block

The sinuses are air filled, bony cavities connected with the nose by means of one or more small openings. If these openings are obstructed by swelling of the mucous membrane lining of the sinuses (as during a cold), equalization of the pressure is difficult. Pain in the cheek bones on either side of the nose, or in the upper jaw, or above the eyes, will result.

The valsalva procedure will relieve sinus pain

For both ear and sinus block, the prudent use of nasal inhalants such as Benzedrex, Afrin, Neosynephrine may be helpful.

A nasal inhalant containing antihistamine, however, should not be used for the reasons stated in the section on drugs below.


Toothaches may occur at altitude due to abscesses, imperfect fillings, inadequately filled root canals. Anyone who suffers from toothache at altitude should see his dentist. However, the pain caused by a sinus block can be mistaken for toothache. If air is able to enter below a filling, the filling may well be blown out as the pilot reaches higher altitude.

Gastrointestinal Pain

Gas pains are caused by the expansion of gas within the digestive tract during ascent into the reduced pressure at altitude. Relief from pain may be accomplished by descent from altitude.

The Common Cold

Don't fly with a common cold. A cold that is a mere discomfort on the ground can become a serious menace to a pilot and his passengers in the air.

Tiredness, irritability, drowsiness and pain are ail symptoms of a cold and work together to make a pilot unsafe in the air. More insidious, however, is the effect a cold may have on the sinuses and on the middle and inner ear. Swollen lymph tissue and mucous membranes may block the sinuses causing disabling pain and pressure vertigo during descent from altitude. Infection of the inner ear, that is a common symptom of a cold, can also produce severe vertigo. The tissue around the nasal end of the Eustachian tube will quite likely be swollen and middle ear problems associated, under normal conditions (see above), with descent from altitude will be severely aggravated. A perforated eardrum is a possible result. Although a perforated eardrum usually heals quickly, in some cases there is permanent hearing impairment or prolonged infection of the middle ear.

Cold remedies do not prevent symptoms. They usually only bring on other problems, drowsiness being the most common.

evolved gases

Nitrogen, always present in body fluids, comes out of solution and forms bubbles if the pressure on the body drops sufficiently as it does during ascent into the higher altitudes. Overweight persons are more susceptible to evolved gas decompression sickness as fatty tissue contains more nitrogen.

Bends is characterized by pain in and around the joints and can become progressively worse, during ascent to higher altitudes.

Chokes are pains in the chest caused by blocking of the smaller pulmonary blood vessels by innumerable small bubbles. In severe cases, there is a sensation of suffocation.

Paresthesia or Creeps is another decompression sickness with symptoms of tingling, itching, cold and warm sensations.

Central nervous system disturbances include visual disturbances, headache and, more rarely, paralysis and sensory disturbances.

Decompression sickness is unpredictable. One of the outcomes may be shock, characterized by faintness, dizziness, nausea, pallor, sweating and even loss of consciousness. Usually the symptoms disappear when a return to the ground is made. However, the symptoms may continue and special treatment (recompression) may be needed.

Decompression sickness, caused by evolved gas, is rare below 20,000 feet. The best defence against this painful problem is a pressurized cabin. Some protection against it can be achieved by breathing 100% oxygen for an hour before ascending to altitudes above 20,000 feet. This action washes the nitrogen out of the blood. Oxygen does not come out of solution or form bubbles. Refrain also from drinking carbonated beverages or eating gas producing foods.

Scuba Diving and Flying

A person that flies in an airplane immediately after engaging in the sport of scuba diving risks severe decompression sickness at much lower altitudes than this problem would normally be expected. The scuba diver uses compressed air in his breathing tanks to counteract the greater pressure of the water on his body. At a depth of 30 feet, his body absorbs twice as much nitrogen as it would on the ground. Ascending to 8000 feet ASL could bring on incapacitating bends. A good rule, if you have dived to a depth below 30 feet, is not to, fly for 24 hours to permit the nitrogen content of the body to return to, normal.