Hypoxia
There is a little known partial solution for the pilot or person who is at an altitude where oxygen deficiency is likely. You can increase the air pressure in you lungs and thereby aid the absorption of oxygen in your lungs by the following process. You can partially pressurize your lungs by only breathing out through 'pursed' lips. You must purse your lips and blow out instead of exhaling normally. Inhale normally but pressurize your lungs when exhaling.
An adult will breath in 3,000 gallons (by volume) of air per day. This includes 600 (20% of total) gallons of oxygen. Your blood system has 25+ trillion (12 zeros) red blood cells (hemoglobin). Each one is capable of loading up four oxygen molecules for distribution throughout the body. when returning to the lungs for a refill they unload CO2 first.
Movement, fear, and anxiety will increase the oxygen requirement. Fatigue and medicines accentuate hypoxia. By the time you have visual problems it is too late. It is up to the pilot to anticipate and prevent hypoxia by the use of supplemental oxygen.
Hypoxia symptoms will vary with the individual. While night vision will begin to be affected at 5000 feet, at 10000 a pilot may feel that everything is just fine-hypoxia. Breathing and respiration are affected but most affected is the brain. The brain uses 20% of the oxygen used by the body. Of the brain the cortex suffers the most and with it goes good judgment. The victim is the last one to know that anything is wrong. Individuals will display completely different physiological and psychological symptoms. By undergoing an altitude chamber flight you can learn the symptoms peculiar to just you.
Mankind evolved expecting to breathe air containing 21% oxygen under 14.7 pounds of pressure. Once man has enough money to fly, this 21% at higher levels of lower pressure this 21% becomes inadequate. Symptoms of hypoxia will occur in the altitudes over five thousand feet. Age is a factor as are the life-style factors of fatigue, drinking, and smoking. The condition of hypoxia because of altitude can become magnified and compounded by human individual factors. Hypoxia is caused only by reduced atmospheric pressures caused by altitude and not by other density altitude factors. As altitude increases arterial blood oxygen pressure lowers so that less oxygen is available to the blood for transfer to the brain. A change of only 4% is sufficient to affect mental function. Once you experience hypoxia and have identified your symptoms you will be more apt to recognize them next time.
Hypoxia is oxygen starvation. Lack of oxygen impairs the whole body but most importantly the brain. The first part of the body to show significant effect from oxygen deficiency is the retina of the eye. Every individual is affected but in different ways and to different degrees. The danger in hypoxia is that it occurs insidiously below the conscious threshold. Hypoxia makes you happy and such happiness in the cockpit is dangerous. The best warning indicator for hypoxia is the altimeter. You will quickly recover by descent to a lower altitude.
Since hypoxia is due to reduced barometric pressure, low-grade hypoxia begins on takeoff. The percentage of oxygen is same but less is reaching the blood stream. Any stress or increase in activity requires more oxygen, up to 8 times more. Pilot performance deterioration begins at takeoff, as well. Slowed response times and inability to deal with complexities due to hypoxia compromise safety. Noticeable oxygen deficiency effects begins at 4000' as safety margins are beginning to erode. The hypoxic symptoms of difficulty breathing or headache may not be obvious or may not occur at all even though there are the foregoing changes in mental status.
I have seen complete personality changes occur after a couple of hours around 12,000'. Symptoms occur such as headache, drowsiness, dizziness, euphoria, tingling, perspiration, or belligerence are typical. Tunnel vision and blue fingernails occur with times as little as 15 minutes above 15,000'. At 16,000' disorientation, lapses of judgment, loss of impulse control, risk-taking behavior, decreased problem solving abilities, impaired memory, mood disturbances, and lowered coordination are common. Unconsciousness occurs in 10 minutes at 20,000'.
All effects are made worse and happen at lower altitudes with fatigue, age, smoking, health habits, and drinking. Oxygen recommended above 10,000 day and 5,000 night. If oxygen is being used, being knowledgeable about the operation of the system and be able to recognize his and the system's warnings of oxygen deficiency is essential. FARs require oxygen if one-half hour above 12,500', crew above 14,000', everybody above 15,000'.
We take 20,000 breaths a day that take in oxygen and exhale carbon dioxide. At altitude the air expands and there is less oxygen available per breath. Above 10,000' supplemental oxygen is recommended. At night 5000' is the recommended level.
There are no reliable signals for the use of oxygen. The brain suffers first and affects the judgment. Oxygen deficiency gives you a high along with a headache, lightheadedness, dizziness, tingling and warmth, poor coordination, impaired judgment, and tunnel vision.
Hypoxia begins when your cells become oxygen deficient. The brain cells are first to be affected. You have two kinds of measures for oxygen deficient performance. Effective performance time (EPT) which is an average charted for many people. Your experience may vary. Time of useful consciousness (TUC) is based on altitude chamber research. Again, your experience may vary. With good training and a good system the hazard of hypoxia is low. The symptoms of carbon monoxide poisoning disappear more slowly than do those of hypoxia.
A hypoxic carpenter would measure ten times instead of twice and cut five times instead of once. Judgment is indecisive and slow. Caffeine, tobacco, dehydration, respiratory problems, age, fatigue, alcohol and nutrition all affect the onset and severity of hypoxia. The most common of all these deficiencies in the general flying population will be dehydration. Take water when you fly and drink it while you fly.
High altitude performance decreases within in 20 to 30 minutes at 18,000'. You have enough time to take defensive measures and descend. At 25,000' your EPT will be less than five minutes. Using oxygen at night and even during the day at lower altitudes will improve flight performance. For the G. A. pilot the nasal cannulas with an oximizer offers the best bang for the buck.
Above 10.000s feet pilot judgment is affected unless supplemental oxygen is available. At night, vision deteriorates above 5000 feet. In good health you normally have 95% oxygen saturation. Below 85% judgment is affected. Nausea can be an early symptom of oxygen deficiency.
More on Hypoxia
Hypoxia - the absence of an adequate supply of oxygen to the tissues that always results in impairment of function. FOUR things must happen to get oxygen to the tissues. The four types of hypoxia each correspond to the failure of one step The last two are unlikely in pilots but possible in passengers, especially while doing any kind of Air Ambulance work.
There are 4 different types of hypoxia:
1. Hypoxic - caused by a reduction in oxygen tension in arterial blood due to altitude or hypoventilation. (i.e. lack of oxygen in the lungs). Get O2 into lungs [failure = hypoxic hypoxia]
2. Hypaemic - a reduction in the oxygen (O2) carrying capacity of blood. Some causes: drugs, anaemia, carbon monoxide in the blood, hemorrhage, smoking. (i.e. not enough O2 in the blood) . Get O2 from lungs into blood [failure = Hypemic (American spelling) hypoxia]
3. Stagnant - reduced blood flow through the tissues. Some causes: the flu, vaso-vagal syncope (fainting), cardiac failure, G-forces (most common). Get O2 around body to tissues [failure = stagnate hypoxia]
4. Histotoxic - the inability of tissues to use normal O2 supply. Causes include: alcohol, narcotics, cyanide, carbon monoxide. Get O2 from blood into tissue [failure = histotoxic hypoxia].
Symptoms:
Personality changes, lack of insight, loss of judgement/memory, euphoria, mental/muscular unco-ordination, sensory loss, cyanosis (purple coloring of skin), hyperventilation, semi-consciousness leading to unconsciousness.
Factors:
Altitude, rate of ascent, duration of exposure, environmental temp, individual tolerance, physical activity, and fatigue.
Time of Useful Consciousness (TUC)
Item: A person who smokes a cigarette before getting into the airplane starts out at a TUC of 3000 feet.
At 18000', it's 20-30mins, at 22000', 10mins, at 25000', 3-5mins, and if you ever get to FL400 it's 15-30seconds.
Effect on night vision:
Altitude............% decrease in visual acuity if O2 is not used
4000...............5
6000.............10
8000.............15
10000...........20
12000...........25
14000...........35
16000...........40