Hypoxia and altitude.

Hypoxia means “reduced oxygen” or “not enough oxygen.” Although any tissue will die if deprived of oxygen long enough, the greatest concern regarding hypoxia during flight is lack of oxygen to the brain, since it is particularly vulnerable to oxygen deprivation.

The first symptoms of hypoxia can include euphoria and a carefree feeling. With increased oxygen starvation, the extremities become less responsive and flying becomes less coordinated.

As hypoxia worsens, the field of vision begins to narrow and instrument interpretation can become difficult. Even with all these symptoms, the effects of hypoxia can cause a pilot to have a false sense of security and be deceived into believing everything is normal.

The symptoms of hypoxia vary with the individual, but common symptoms include: • Cyanosis (blue fingernails and lips) • Headache • Decreased response to stimuli and increased reaction time • Impaired judgment • Euphoria • Visual impairment • Drowsiness • Lightheaded or dizzy sensation • Tingling in fingers and toes • Numbness

The term “time of useful consciousness” describes the maximum time the pilot has to make rational, life-saving decisions and carry them out at a given altitude without supplemental oxygen. As altitude increases above 10,000 feet, the symptoms of hypoxia increase in severity, and the time of useful consciousness rapidly decreases.

The reactions of the average person become impaired at an altitude of about 10,000 feet, but for some people impairment can occur at an altitude as low as 5,000 feet.

Since symptoms of hypoxia can be different for each individual, the ability to recognize hypoxia can be greatly improved by experiencing and witnessing the effects of it during an altitude chamber “flight.”

Since many of the symptoms of hyperventilation are similar to those of hypoxia, it is important to correctly diagnose and treat the proper condition.

Without supplemental oxygen, an individual’s night vision declines measurably at pressure altitudes above 4,000 feet.

As altitude increases, the available oxygen decreases, degrading night vision. Compounding the problem is fatigue, which minimizes physiological well being. Adding fatigue to high altitude exposure is a recipe for disaster. In fact, if flying at night at an altitude of 12,000 feet, the pilot may actually see elements of his or her normal vision missing or not in focus.

For the pilot suffering the effects of hypoxic hypoxia, a simple descent to a lower altitude may not be sufficient to reestablish vision. For example, a climb from 8,000 feet to 12,000 feet for 30 minutes does not mean a descent to 8,000 feet will rectify the problem. Visual acuity may not be regained for over an hour.

Treatment for hypoxia includes flying at lower altitudes and/or using supplemental oxygen. All pilots are susceptible to the effects of oxygen starvation, regardless of physical endurance or acclimatization.

In a typical pressurization system, the cabin, flight compartment, and baggage compartments are incorporated into a sealed unit capable of containing air under a pressure higher than outside atmospheric pressure.

Item 1 | Flight crew member or cabin crew member | (a) For any period exceeding 30 minutes when the cabin pressure altitude is continuously at least FL 125 but less than FL 140, there must be supply for the entire period. (b) For any period when the cabin pressure altitude is at least FL 140, there must be supply for the entire period.

(4) Each flight crew member must use the supplemental oxygen that is made available to each of them in accordance with the supply requirements mentioned in column 2 of item 1 of Table 26.43 (2).

Item 2 | Passenger | (a) For any period when the cabin pressure altitude is at least FL 150, there must be supply for the entire period.

Pilots should consider whether supplemental oxygen should be carried even if it is not required since hypoxia is insidious, and its onset is determined by many variables.