5.1 Aviation Physiology, Hypoxia & Hyperventilation

1. Aviation Physiology

There are few regulations that tell a pilot whether he/she is fit to fly. You have to make the decision on whether you are fit to fly based on common sense and experience.

Not being fit for flight may result in symptoms such as reduced alertness, slower reaction time, poor decision making all the way to loss of consciousness.

Many medical conditions that may lead to a problem in flight can be diagnosed before the flight takes place. These conditions include fatigue, ingestion of alcohol or drugs, activities that may lead to decompression sickness, colds and flu, and middle ear and sinus discomfort.

Individuals suffering from conditions that could result in sudden or subtle incapacitation, such as epilepsy, heart disease or uncontrolled diabetes should probably not fly at all.

Note

Although the CARs only require HG pilots to have a Class 4 medical to fly in controlled airspace, in truth, all HG pilots should be able to meet the requirements for a Class 4 medical.

In some cases, healthy pilots may experience hypoxia, hyperventilation, disorientation and/or hypothermia during flight. It is important that you be able to recognize the symptoms for those conditions and know what to do if they occur to you.

2. Hypoxia

Hypoxia is a result of a lack of sufficient oxygen for the body to operate normally. The onset of hypoxia is difficult to detect as the body has no built-in alarm system to indicate it is not getting enough oxygen.

Symptoms

Even minor hypoxia impairs night vision and slows reaction time. More serious hypoxia interferes with reasoning, gives rise to unusual fatigue and finally produces unconsciousness. An early symptom of hypoxia may be a feeling of well-being (euphoria) during which the pilot is unaware of any impairment.

The Rules

• To avoid hypoxia, pilots should not fly above 10,000 ft ASL without supplemental oxygen.
• The CARs specify that pilots should not fly between 10,000 and 13,000 ft ASL for more than 30 minutes without supplemental oxygen.

Note

Many out-of-shape pilots or pilots living close to sea level may encounter the effect of hypoxia faster. These pilots should stay below 10,000 ft ASL.

Relief

Relief from hypoxia can be achieved by breathing oxygen or descending to lower altitudes.

3. Hyperventilation

Hyperventilation most commonly occurs in association with anxiety, fear, or during intense concentration. It means breathing at a faster and/or deeper rate than you have to for the existing work level.

The Cause

Normally the rate of breathing is controlled by the amount of carbon dioxide in the lungs and in the blood. When a pilot hyperventilates, carbon dioxide is blown off and the level of carbon dioxide in the blood drops below normal. This, in turn, causes the arteries to the brain to constrict and reduces the blood supply. Continuous hyperventilation can cause unconsciousness.

Symptoms

• May include dizziness, a feeling of coldness, a sensation like a tight band around the head, pins and needles in the hands and feet, and cramping and spasms of the hands and feet.
• Paradoxically, pilots will often feel as though they cannot get enough air.

Relief

It may be difficult for a pilot to differentiate between hypoxia and hyperventilation. Rather than trying to make a diagnostic, pilots should consciously slow the rate of breathing to 10-12 breaths per minute and not breathe deeply. The lowering of the respiratory rate should eliminate the symptoms and the pilot can then resume a normal breathing pattern.