In simple terms, hypoxia means that you don’t have enough oxygen to function properly. There are many ways that this can happen and it doesn’t have to be as complete or as devastating as the problem with Payne Stewart’s airplane. Most of us won’t fly over 12,500 feet in our Birddogs. But a review of HYPOXIA will help us all to remember the effects of the lack of oxygen (hypoxia). There are other reasons to have decreased oxygen in our body. This may very well hamper and impair our performance and decrease our ability to fly. For those of us who have been to the "altitude chamber," the effects of decreased oxygen are known. Let us review "more than you want to know" about oxygen in the systems of our body.

If a person’s body, lungs and all systems are properly functioning, the blood in the arteries will be 100% saturated with oxygen (for the Navy pilots, this is why the blood is red). Normal blood is saturated in the lungs and the oxygen is carried to all organs, tissues and parts of the body by the arteries and the function of the heart (the pump). Blood returning to the heart from the organs, tissues and parts return in veins. Blood returning in the veins is approximately 75% saturated with oxygen (for the Navy pilots, that is why the blood is blue).

There are four types of HYPOXIA:

1. Hypoxic hypoxia is the most common and is caused by decreased oxygen in air or the inability to diffuse the oxygen across the lungs. If this happens, the person has less than 100% saturation of the blood in the arteries. This can happen if you are at an altitude where the oxygen content of air is low (i.e., over 12,500 feet). Another problem would be if a person’s lungs were damaged so oxygen transfer was impaired (all you smokers beware!).

2. Hypemic hypoxia is caused by the reduction of the oxygen carrying capacity of the blood. Anemia (low hemoglobin) can cause this. The oxygen is available, but there isn’t enough good blood to carry the oxygen. BIRDDOGERS THINK ABOUT THIS…………Carbon monoxide poisoning will cause this type of HYPOXIA! The blood holds on to the carbon monoxide from the exhaust leak in your engine and your capacity to carry oxygen decreases….. you become hypoxic!

3. Stagnant hypoxia is caused by reduced cardiac output (the pump isn’t working good enough) or by
venous pooling during high G force stresses. We are all getting older and we have to remember that the function of the heart is essential for pumping the oxygenated blood.

4. Histotoxic hypoxia occurs when all systems are working but the cells can’t "take" the oxygen from the blood. The oxygen is available. Alcohol or cyanide poisoning can cause this.

Stages of Hypoxia:

1. Indifferent….At the beginning, the person may not know there is a problem. The first effect is the depression of the function of the eye to adapt to dark and color. This can happen at an altitude as low as 5,000 feet.

2. Compensatory……Denial is common (That is why USAF crewmembers go to the altitude chamber, recognize effects, and take action.). The respiration rate, heart rate, blood pressure, and cardiac output can rise.

3. Disturbance…..Obvious symptoms begin. These are different for each person (i.e., numbness, tingling, etc.).

4. Critical ……..Loss of consciousness!

Symptoms are different for each individual. Some things are very common. The person may experience a "peculiar" or "dizzy" feeling. He/she may exhibit euphoria or inappropriate thoughts or actions. Problems with sight can include loss of peripheral vision, dimming, and diminished night vision. There is a poor response to verbal commands and forgetfulness. The ability to control the aircraft is affected. If prolonged, headache and nausea can occur.

There are many other "high power" implications of HYPOXIA that are not necessary to be covered in this article. They are very specific to high altitude flight. The time of useful consciousness (TUC) is greatly decreased as you go over 40,000 feet. If you breathe air (not oxygen through your mask), the oxygen from your blood is actually taken out into the air. This gives you less conscious time.

Causes of HYPOXIA in flight:

1. Failure of oxygen delivery (the regulator doesn’t work, there is no oxygen in the tanks, etc.)
2. Carbon monoxide inhalation ("birddogers" check out the number 2 cause!)
3. Cabin pressure failure

Prevention:

1. Early recognition of the symptoms
2. Proper use of oxygen equipment
3. Good maintenance of the oxygen equipment
4. Preflight all oxygen equipment
5. Strict adherence to the oxygen requirements (required above 12,500 feet)

This is a review for many of you, but it is one more item to pack in the back of our heads. For the "Birddoger", the message about HYPOXIA is clear. HYPOXIA is the lack of oxygen in all of the functioning parts of the body. We don’t have to worry about extreme altitude. But any problem that decreases our ability to carry the oxygen from the air to our body systems can cause HYPOXIA. We may have bad lungs and can’t absorb the available oxygen or our heart may not pump as well as when we were young. We may have absorbed carbon monoxide so that we can’t absorb the oxygen, even though our lungs are working normally. Anemia or some medications could not give us enough red blood cells to carry enough oxygen. These are things to ponder. Remember, the number two reason for HYPOXIA is carbon monoxide poisoning. The effect of the HYPOXIA could be just enough to hamper your ability to fly and land the airplane. Combine this problem with decreased night vision (caused by decreased oxygen) and the result would not be good.

Fly Safe! REX 79

Written for Birddog owners by Dr. Steve Frushour, IBDA Aero-Medical Officer