Physiological Effects of Altitude

Flying at higher altitudes exposes pilots and passengers to reduced oxygen levels, pressure changes, and other environmental factors that can affect physical and mental performance. Understanding these physiological effects is essential for maintaining safety and well-being during flight.

1. Hypoxia

Hypoxia occurs when the body is deprived of adequate oxygen, which is more likely at higher altitudes due to lower air pressure.

1.1 Types of Hypoxia

• Hypoxic Hypoxia: Caused by reduced oxygen levels at altitude due to lower atmospheric pressure.
• Hypemic Hypoxia: Occurs when the blood cannot carry sufficient oxygen, such as in cases of carbon monoxide poisoning or anemia.
• Stagnant Hypoxia: Caused by poor blood circulation, such as in cases of G-forces or prolonged sitting.
• Histotoxic Hypoxia: Occurs when the body’s cells cannot use oxygen effectively, often due to alcohol or drug use.

1.2 Symptoms of Hypoxia

• Fatigue and drowsiness.
• Impaired judgment and decision-making.
• Headache and dizziness.
• Shortness of breath and rapid breathing.
• Blue coloration of lips or fingernails (cyanosis).
• Euphoria or a false sense of well-being.

1.3 Preventing and Managing Hypoxia

• Use supplemental oxygen above 10,000 feet during the day and 5,000 feet at night (or as required by FAR 91.211).
• Monitor oxygen saturation levels with a pulse oximeter.
• Descend to a lower altitude if hypoxia symptoms are detected.

2. Hyperventilation

Hyperventilation occurs when breathing is too rapid or deep, leading to an excessive loss of carbon dioxide in the blood.

2.1 Causes

• Anxiety or stress during flight.
• Improper use of oxygen systems.

2.2 Symptoms

• Dizziness and lightheadedness.
• Tingling in the fingers and toes.
• Muscle spasms or cramps.
• Confusion or inability to concentrate.

2.3 Managing Hyperventilation

• Consciously slow breathing to a normal rate.
• Breathe into a paper bag (if available) to restore carbon dioxide levels.
• Focus on remaining calm and relaxed.

3. Decompression Sickness (DCS)

Decompression sickness, also known as “the bends,” occurs when nitrogen dissolved in the blood forms bubbles due to rapid decreases in air pressure.

3.1 Causes

• Flying at high altitudes without pressurization.
• Ascending too quickly after recent scuba diving.

3.2 Symptoms

• Joint pain (especially in the knees, shoulders, or elbows).
• Nausea and dizziness.
• Shortness of breath or chest pain.
• Fatigue and confusion.

3.3 Prevention

• Pressurize the cabin or use supplemental oxygen when flying above 18,000 feet.
• Wait at least 24 hours after scuba diving before flying.
• Ascend gradually to allow nitrogen to safely leave the body.

3.4 Treatment

• Descend to a lower altitude immediately.
• Administer 100% oxygen if available.
• Seek medical attention as soon as possible.

4. Vision Impairment

Altitude can affect vision, particularly at night, due to reduced oxygen levels.

4.1 Effects on Vision

• Night Vision Impairment: Even mild hypoxia can reduce night vision by up to 25%.
• Peripheral Vision Loss: Hypoxia or fatigue can narrow a pilot’s field of view.

4.2 Preventing Vision Impairment

• Use supplemental oxygen above 5,000 feet at night to improve oxygen delivery to the eyes.
• Allow time for eyes to adjust to darkness (30 minutes in low light).

5. Other Physiological Effects

5.1 Fatigue

• High altitudes can cause fatigue due to reduced oxygen availability.
• Plan shorter flights or ensure adequate rest before operating at high altitudes.

5.2 Gas Expansion

• Reduced atmospheric pressure can cause gases in the body (e.g., in the ears, sinuses, or gastrointestinal tract) to expand, leading to discomfort or pain.
• Perform the Valsalva maneuver to relieve pressure in the ears.

6. Regulations Related to Altitude

The FAA provides guidelines on oxygen use to prevent altitude-related physiological issues:

• Above 12,500 feet MSL: Oxygen is required for crew after 30 minutes.
• Above 14,000 feet MSL: Oxygen is required for crew at all times.
• Above 15,000 feet MSL: Oxygen must be available for passengers.

7. Practical Tips for Pilots

• Monitor yourself and passengers for signs of hypoxia or other altitude-related symptoms.
• Plan flights to avoid prolonged exposure to high altitudes when supplemental oxygen is not available.
• Use a pulse oximeter to measure blood oxygen levels during flight.
• Stay hydrated and avoid alcohol or sedatives before flying at higher altitudes.

8. Conclusion

Understanding the physiological effects of altitude is essential for safe flight operations. By recognizing the symptoms of hypoxia, hyperventilation, and other altitude-related issues, and by adhering to FAA regulations, pilots can mitigate risks and ensure the safety of everyone on board.