Hypoxia in Helicopter Pilots

Welcome back to Helicopter Lessons in 10 Minutes or Less! I'm Jacob and this video covers Hypoxia and expands into the Aeromedical topics. That is, the topics covering how the environment and substances you put into your body can affect how you perform as an aviator. Be sure to hit like and leave your video ideas in the comments below!
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Hypoxia is simply a state of oxygen deficiency in the body that impairs brain function and other organs. In other words, the brain can't get enough oxygen. There are a few reasons this can and so Hypoxia can be broken down into 4 types: Hypoxic, Hypemic, Histotoxic, and Stagnant.
1. Hypoxic Hypoxia: while sounding redundant, this type of hypoxia occurs due to increasing altitude. As you fly higher, the air is thinner and there's less oxygen to breath. So naturally your brain is at a deficit.
2. Hypemic Hypoxia: this is a reduction in carrying capacity of the blood. Also known as Anemic Hypoxia, it occurs when there is a reduction in hemoglobin in the red blood cells that are able to combine with oxygen molecules.
3. Histotoxic Hypoxia: this results in interference with the use of oxygen by bodily tissues. It's as if the tissues block oxygen from absorbing. Typically caused by alcohol, narcotics, or poisonous compounds that prevent absorption.
4. Stagnant Hypoxia: this is a circulation problem. There may be enough oxygen in the environment but it can't get to the tissues that need it. This can be stagnant blood circulation caused by G forces, compressed blood vessels from tight clothing or sitting in a way that restricts blood flow, or a medical condition that results in poor circulation.
A simple way to visualize these 4 types is to use a school bus analogy. This includes the children (oxygen), the school (brain and other tissues), and the bus (carrying capacity of oxygen in the blood). Hypoxic hypoxia would mean there aren't enough children to pick up. Hypemic hypoxia would be like the bus is a short bus or has reduced carrying capacity so it has to work harder and make more trips. Histotoxic hypoxia would be like the school not allowing any more children to get off of the bus to enter the school. Stagnant hypoxia would be like the bus can't make it up the hill to get to the school in the first place.
Taking it a step further, there are different stages of hypoxic hypoxia (the one associated with altitude). This type progresses as altitude increases and becomes more dangerous for aviators. From 0'-10,000' Pressure Altitude (PA) this is considered the Indifferent Stage. This is where most helicopters fly and there's negligible effects here because oxygen is plentiful this close to sea level. The main thing that happens physiologically at these levels due to hypoxia is a mild deterioration of night vision above 4000'-5000'. Above this altitude, from 10,000'-15,000' PA is known as the Compensatory Stage. That means your bodily works harder to compensate for the lack of oxygen. Pulse rate, blood pressure, and circulation increase. The bus driver drives faster looking for more kids to bring to the school because the school says there's not enough children. After 10-15 minutes here you may feel drowsy and make simple errors in judgement. Some even claim that they don't see color differences in cockpit instruments. Some may not notice anything at all. Above this is the Disturbance Stage from 15,000'-20,000' PA. You could become unconscious, feel fatigue, dizziness, sleepy, breathlessness, or even like a drunken euphoria where everything feels great. Your fingertips and lips could be turning blue due to cyanosis. All of the above make it a dangerous state to fly in. Lastly, the Critical Stage is above 20,000' PA. Extreme confusion and unconsciousness could occur within 3-5 minutes here resulting in an almost certain crash.
So how do you compensate? Either limit exposure in these altitudes by Descending, using Supplemental Oxygen, or flying in a Pressurize Cabin. 100% oxygen can reduce the effects of hypoxia within just a few breaths to a few minutes. If you have to fly at these altitudes, plan accordingly. The Federal Aviation Association (FAA) mandates supplemental oxygen between 12,500'-14,000' PA after 30 minutes and immediately above 14,000' PA. The military branches outline even further restrictions.
But that wraps up Hypoxia. Thanks for watching. Be sure to hit like and subscribe. As always, this is Helicopter Lessons in 10 Minutes or Less. I'm Jacob, safe flying.