Hypoxia

What Does This Mean for a Pilot?

You’re trying to learn how to fly planes, not enter the medical industry right? I’m sure you are aware briefly of what happens to your body when you climb to higher altitudes. Though hypoxia for the average GA pilot may never prove to be something they experience (unless they are flying at higher altitudes that require supplemental oxygen), it is still very important information to know. Especially if you have chosen aviation as a career. I hope this information gives you a much better understanding of hypoxia and not just the basic knowledge needed to pass your check ride. If there are any specific questions you have about hypoxia, please feel free to fill out this form with your question. I will either e-mail you back or update this page with the answer. Ok, Lets dive into it.

The body requires oxygen to perform even the most basic functions. Without it, those functions cease to happen. The result of an imbalance between oxygen supply and the oxygen required of the body tissue is called hypoxia. Hypoxia is an illness caused by lack of oxygen reaching the tissue. In the most basic words to explain the definition of hypoxia, I would simply say that hypoxia is when a person doesn’t have enough oxygen.

Types of Hypoxia

 Hypoxic Hypoxia

Hypoxic Hypoxia occurs when there is an insufficient supply of oxygen all together. This can occur with things like a blocked airway or when one is drowning. However, we are more concerned with how this applies to us as a pilot right? As a pilot, we should know that at higher altitudes, there is a reduction in pressure. So though there is the same percentage of oxygen, there will be fewer molecules available at the pressure required for them to pass through your respiratory system. We will come back to this a little later.

 Hypemic Hypoxia

While hypoxic hypoxia is a lack of oxygen inhaled, Hypemic Hypoxia is a lack of oxygen in the blood. This type of hypoxia is the inability of the blood cells to carry sufficient amount of oxygen to the tissue. This can by caused by low hemoglobin levels or from different blood diseases. However, as a pilot, you should be aware of the most common cause, which is CO (carbon monoxide) poisoning. Hemoglobin is the blood molecules that transport oxygen. CO competes directly with the oxygen molecules for binding space on the hemoglobin. However, CO binds around 200 times greater than that of the oxygen molecule. When you get CO poisoning, your hemoglobin is unable to bind the oxygen molecules because of the carbon monoxide bind. The best way I can explain this is to imagine the blood cell as a bus with oxygen molecules filling up each seat. Then along comes a carbon monoxide molecule and it bumps off the oxygen molecules. Kind of like playing king of the hill, but the oxygen molecules can’t bump the CO molecule back off because it’s bind is much stronger then that of an oxygen molecule. This creates a lack of oxygen being carried by the blood to the tissue.Another thing to note is that when donating blood, it can take several weeks for your blood volume to return to normal. The effects at sea level may not be a big deal, but this is an added risk of hypemic hypoxia at higher altitudes.

Stagnant Hypoxia

Stagnant Hypoxia is an inadequate circulation of the blood, causing the oxygen molecules to never make it to the tissue. Have you ever sat in a weird position and caused your leg to “fall asleep”? This is the perfect example of stagnant hypoxia. The blood flow is being clogged or shut off from reaching the tissue in the leg. As pilots, we need to pay special attention to this because this can occur with excessive acceleration of gravity, also known as “pulling Gs”. Most commonly experienced by acrobatic or fighter pilots. This form of hypoxia can also be caused by cold temperatures, which will reduce the circulation and decrease the blood flow.

Histotoxic Hypoxia

Histotoxic Hypoxia is the inability of the cells to effectively use oxygen. You’re breathing in enough oxygen, your hemoglobin is carrying sufficient oxygen, and your blood is flowing all the oxygen to the tissues. However, with histotoxic hypoxia, your tissues are unable to make any use of the oxygen being transported to it. This is caused by alcohol or drugs (or poisons). To give you an idea of the effects alcohol can have on a pilot, research has shown that each ounce of alcohol, equates to 2,000ft of altitude. Next time you go out drinking with your friends, try playing the “what altitude are you at” game. Remember though, 8hr bottle to throttle!!  

Hypoxic Hypoxia Thresholds

So lets go back to hypoxic hypoxia, which I believe is the most common form of hypoxia when it comes to pilots. Just like we discussed previously, we know that as we ascend in altitude, the atmospheric pressure decreases, but lets take a closer look at different threshold altitudes. What is happening at different altitudes? First lets start off with 5,000ft. I remember on my initial commercial check ride, my examiner gave me a scenario of at night flight at 10,000ft. He stated that my passenger started showing signs of hypoxia and asked me what my plan would be. I remember saying something along the lines of descending down to 5,000ft based off the surrounding airspace.

Symptoms

The signs and symptoms of can vary between different people, and by how long the symptoms have been present. So how can we tell if we or someone else is experiencing hypoxia? The following is a list of the different things to look out for:

Effect on The Body

The organs most effected by hypoxia are the brain, heart, and liver. If hypoxia is extreme enough, irreversible damage can occur within as little as 4 minutes. Coma, seizures, and death may occur in severe cases. Chronic, milder hypoxia can also cause damage to the major organs of the body. Chronic hypoxia tends to have different symptoms such as fatigue, apathy, a delayed reaction time, or reduced work capacity. Acute hypoxia symptoms often include motor incoordination and impaired judgement causing people to think that a person with hypoxia is intoxicated with alcohol.