HYPOXIA

Hypoxia is a medical condition where there is a deficiency of oxygen in the tissues and organs of the body. This can occur due to various reasons, including respiratory disorders, circulatory problems, or exposure to high altitudes.

• Hypoxic hypoxia: Hypoxic hypoxia occurs when there is insufficient oxygen in the blood to meet the body’s needs, primarily due to inadequate oxygenation at the lungs. This condition results from a decrease in the partial pressure of oxygen in arterial blood. It is caused when flying a depressurized aircraft at high altitudes.

Hypoxia symptoms appear in stages depending on the cabin altitude. These stages are:

Indifferent Stage/Zone (Ground Level to 10 000 ft): Dark adaptation is impaired (can occur as low as 5000 ft). New task performance may be affected. There is a slight increase in heart and breathing rates.

Compensatory Stage/Zone (10 000 ft to 15 000 ft): Physiological responses attempt to maintain balance against hypoxia. Respiratory volume, cardiac output and blood pressure all increase. Symptoms include drowsiness, decreased judgment and memory, difficulty in tasks requiring mental alertness or fine motor skills.

Disturbance Stage/Zone (15 000 ft to 20 000 ft): Physiological mechanisms are inadequate for tissue oxygenation. Symptoms include dizziness, sleepiness, headache, fatigue, severe motor performance impairment, loss of judgment.

Critical Stage/Zone (20 000 ft to 23 000 ft): Rapid decline in mental performance, onset of confusion and dizziness within minutes, complete incapacitation with loss of consciousness occur, often without warning.

Typically, a healthy individual can compensate for altitudes up to approximately 10 000 - 12 000 ft.

During decreasing atmospheric pressure, hypoxia symptoms appear. At altitudes as low as 5000 ft the body reacts. Night vision is impaired first, then performance reduces and heart and breathing rates increase.