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Human respiration

Human Factors, Altitude Effects

Human factors is a combination of aviation medicine, psychology, engineering and ergonomics. It encompasses all of these factors trying to understand the man/machine interface in the aircraft. It has its roots in aviation accident investigations resolving these where no clear technical cause could be found when aircraft became more and more reliable over the years.

The air around us keeps us alive and the aircraft flying. The higher we go the thinner the air gets and this has an effect on the aircraft but on the pilot too as with every breath the pilot takes, less and less oxygen is available.

Hypoxia and hyperventilation were already discussed in our previous article, here we delve deeper in other effects altitude can have on our body.

Medical factors

Hypoxia is a state of oxygen deficiency in the human body and the results are impaired functions of the brain and other organs. The effects of hypoxia in a pilot can be devastating if not understood properly. It is also known as altitude sickness.

Hyperventilation is an overly active respiration resulting in too much carbon dioxide (CO2) blow off from the lungs due to stressful situations in flight. It can occur at any altitude and is easily taken care off.

But aside from these obvious effects there are more medical fact pilots need to be aware of. Especially after such minor issues as having a slight cold or even if the pilot or crew member is also a scuba diver enthusiast.

Ear block

Eustachian Block

During ascent of the aircraft the cabin pressure decreases and the air inside the middle ear will push the eustachian tube open and equalizes pressure by escaping into the nasal passages. This process usually goes without any problem unless the person has a severe cold or the flu.

The reverse happens during descent, higher outside air pressure needs to be equalized with the eustachian tube and normally this happens by swallowing, yawning, tensing muscles in the throat. Or by closing the mouth, pinching the nose and attempting to blow through the nostrils (Valsalva maneuver).

An upper respiratory infection such as a cold or sore throat can produce enough congestion around the eustachian tube that pressure equalization is difficult or even impossible to clear (ear block).

This will result in severe pain and possible loss of hearing for hours or even days. Rupture of the ear drum can occur during flight or afterwards and an infection may be the result. A emergency visit to a physician will be advisable when this happens.

IMPORTANT: Prevent this condition by not flying when you have a respiratory infection or suffer from a nasal allergic reaction.

Sinus block

Again, during ascent and descent air pressure in the sinuses will equalize with cabin pressure through small openings that connect the nasal passage to the sinuses. Any blockage due to a cold, respiratory infection or a nasal allergic reaction will result in difficulty equalizing these pressures.

This sinus block can occur in the frontal sinuses above each eye brow or upper cheek. Resulting in severe pain in these areas, maybe even pain in the upper teeth, bloody mucus may also come from the nasal passages.

Preventing a sinus block is easy: do not fly with these medical conditions, and should it happen: visit your physician if problems do not clear soon after landing.

Decompression sickness

During scuba diving the body may build up excess nitrogen. If the passenger or crew member does not allow enough time to get rid of this gas decompression sickness may occur during exposure to low altitude and this creates an serious inflight emergency.

It is a form of joint pain and the effects the patient suffer from are called: the bends.

After diving the recommended waiting time before flying higher than 8000 feet after a dive which has not required a controlled ascent is at least 12 hours. Should the dive required a controlled ascent then one should wait at least 24 hours before any flight is attempted. The altitudes mentioned here are the actual flight altitudes and not pressurized cabin altitudes!

Carbon monoxide poisoning

Carbon monoxide poisoning

Carbon monoxide (CO) is an odorless, colorless and tasteless gas and you find it in exhaust fumes from aircraft engines and heaters. It binds very easy to the hemoglobin in the red blood cells thus preventing oxygen molecules to be transported by the blood. The result is hypoxia and possibly death.

Prevention is easy: have the engine exhaust checked regularly and if you smell exhaust fumes: open the fresh air vents. Most cockpits have a CO detector which changes color when it detects carbon monoxide. Do check the expiry date on the detector and renew when the time comes!

Written by EAI.

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