Night Effect on Vision.  
Acuity Threshold - the distance from your eye at which it reflects enough light to stimulate your eye. Your focal (foveal) vision provides high visual acuity, good color vision, and resolution of fine detail & object recognition but demands conscious awareness. Your peripheral (ambient) vision provides low visual acuity, poor color vision and doesn't necessarily provoke conscious awareness but it is sensitive to low light levels & movement. (Hence, if you're looking for something in the distance (e.g. another aircraft), scan the sky using your peripheral vision - it will pick up relative movement before your focal vision). The foveal vision uses the cones whilst peripheral uses the rods. The first area of the eye to be effected by lack of oxygen is the rod, and as it is these, which are sensitive to low light levels, it results in a degradation of visual acuity at night.

About Hypoxia
20% of every breath intake is oxygen that gives hemoglobin 90% saturation. When the level of saturation reaches 85% on intake your judgement is affected. This is hypoxia and you will be unaware of its effects.

You can give parts of your body hypoxia by shutting off the flow of blood. During this stagnant hypoxia you will feel the tingling of parts of your body as though they were recovering from being 'asleep'. In the presence of carbon monoxide (CO) you have hypemic hypoxia because the hemoglobin fills with CO instead of the oxygen. When the hemoglobin contains CO it cannot use the oxygen that it does have. This inability to use the oxygen is called histotoxic hypoxia. The kind of hypoxia, related to high altitude flying, is called hypoxic hypoxia.

When hypoxic the body tries to compensate by increasing the rate of breathing, increasing the depth of breathing as well as upping the pulse rate. These changes work only to a limited extent below 12,000 feet. Above 8,000 feet without supplemental oxygen a pilot is more likely to make mistakes without being aware of them. There are residual effect of hypoxia that can carry all the way through the instrument approach and landing.

Sea level oxygen saturation may be as high as 99'%. Hospital patients are normally maintained into the low 90s. At 5000 feet saturation is 95% and at 10,000 you are down to 90% and can decrease to 80% with time. Hypoxia is there whether you are aware of it or not. There is a $300 finger clip that will give a digital readout of your saturation level. The FARs do not adequately address the supplemental oxygen problem.

You Won't Know Hypoxia
--Symptoms are excessive happiness, sense of well being, or aggressive anger.
--Poor judgment, impaired vision, forgetfulness, decreased attention and coordination also occur.
--All of the foregoing can occur individually or in concert with any of the others.
--Physically you may have blue skin, purple fingernails, blue lips, a headache or dizziness.
--Over time hypoxia will cause unconsciousness.
--The worst part of hypoxia is that the victim will be totally unaware of the sequence from beginning to end.
--While crew must use oxygen, passengers have the right of refusal.
--Use of oxygen is best begun at 10,000 day and 5,000 night.

Smoking
The smoking of tobacco is a form of self imposed physical and psychological stress that constitutes an immediate and on-going threat to health and safety. A long-term suicide activity. A smoker may deny that drugs are a part of his life. He lies in the face of facts. The whole purpose of a cigarette is to get a nicotine fix. Different from cocaine or heroin? How? The person who smokes is a health and economic hazard to everyone. The residue remains on his person, clothes, possessions, and associates.

Nicotine is an addictive psychotropic that can either stimulate or depress. Immediate side effects can be constriction of blood passages, visual degeneration especially at night, reduced lung capacity and nicotine and coffee together multiply the harmful effect of each. The individual ability to assess the effect of any drug is reduced in the taking. Drug interactions are a most common difficulty.

The smoker will die younger, have poorer health, and will suffer considerably in the process. Smoking makes worse the negative effects of radiation, carbon monoxide, and lack of fluids. Smoking deprives the heart of oxygen, constricts the arteries, alters nerve impulses to the heart and lungs, weakens muscles, causes abdominal cramping, and nausea. Nicotine itself decreases the body's ability to adapt to stress. Nicotine withdrawal symptoms include depression, irritability, difficulty in concentration, decreased heart rate, fall in blood pressure, tension, and impaired performance.

These symptoms are worse if withdrawal occurs. It is not possible to avoid withdrawal while flying commercially since cabin pressure is kept at 8000'. Recovery from withdrawal can occur in as little as eight seconds after inhalation of nicotine-laden smoke. This is both a physical and psychological release. The victim has been sucked into an addiction by a combination of governmental and economic interests. The addictive process is entirely deliberate. Cigarettes were sold at four cents a pack in World War Two. The military still gives a ten-minute smoking break every hour. College 'Judas Goats' were paid handsome sums just to attend college functions and give away free cigarettes. Free distributions were made at fairs and other public functions mostly frequented by the young. The Federal Government has through its agricultural agencies and congressional mandates required that tobacco farmers produce tobacco of a relatively high nicotine content.  Because of their high nicotine content American cigarettes are favored the world over by the addicted.   It is illegal to produce and sell tobacco that is below a very specific level of nicotine in the U.S. . Another government sponsored health program?

Psychological advertising and selective groups have been targeted by the cigarette industry to get as many addicted as possible. Government subsidies have supported these activities both directly and indirectly. The recovery from nicotine withdrawal carries with it the side effect of carbon monoxide poisoning. The carbon monoxide (CO) of cigarette smoke combines with the hemoglobin in blood at a rate of 250 to 1 times more easily than does oxygen. As little as one part CO to 20,000 (.005.%)parts of air is enough to begin the weakening the thought processes of the brain.

A flying smoker starts with as much as 10% carbo-hemoglobin level. This means a smoker is halfway to the 20% level, which can cause a headache, confusion, dizziness and impairment of judgment. CO poisoning is fatal and smokers are already 1/3 of the way there. Perhaps smokers should wear CO detectors on their microphone. Engine exhaust can have as high as 7% CO. Do not fly if you smell exhaust fumes, which are always accompanied by CO, which has no odor. The CO level of a smoker is usually between 4 and 10 percent just after a cigarette. A frequent smoker can have up to 10% CO saturation at all times. Any additional CO from another source would compound the problem of the smoker.

You can't do anything to recover from carbon monoxide poisoning caused by smoking; it's there just as though you had a direct connection from an exhaust pipe into your lungs. Engine exhaust in vehicles has 7% CO. Working around cars, even in partially closed spaces, can be doubly hazardous the one's health. If your work can be a matter of life-or-death your smoking may well cause a problem. CO poisoning reduces visual acuity, brightness discrimination and dark adaptations to a significant degree because of hypoxia. At sea level, three successive cigarettes gives a night driving vision capability identical to what the non-smoker has at 8,000' in the mountains. Reversal of these effects will not occur until five hours after your last cigarette.

Susceptibility to CO poisoning increases with altitude due to the propensity of CO to enter blood. This prevents the blood from being able to transport adequate oxygen to the body's cells. The hypemic hypoxia of the smoker reduces his oxygen intake by 5-10 % of normal capacity. The fact that smokers are hypoxic means that we can expect smokers to feel anxiety, forgetfulness, irritability, confusion, and altered judgment with every cigarette. Judgment, math ability, and reasoning will be affected. The indication is that smokers are more likely to enter into personal arguments and show lack of both good judgment and logical reasoning ability in those arguments. Very small amounts of CO over a period of time will reduce a person's ability to perform safely. It is the length of exposure as well as the amount that makes the critical difference. This lack of oxygen to the brain impairs judgment and diminishes the ability to make reasoned decisions. The pack-a-day smoker will have a chronic 10% CO level. CO effects are accumulative so that any additional automotive pollution or altitude will increase the percentage of CO.

Any onset of sluggishness, warmth, and tightness across the head is an early symptom of CO poisoning. A headache, weakness, dizziness and dimming of vision comes next. You won't be aware when you lose strength, vomit, convulse, and enter a coma. A breath of fresh air will not revive you. Several days may be required for full recovery. The smoker is betting against a CO impairment that has already occurred and can only become worse. Carbon monoxide and other toxins in tobacco smoke interfere with the oxygen-carrying capacity of red blood cells. Less oxygen means less energy. Smoking causes an accumulation of mucus in the windpipe and bronchial tubes, constricts blood vessels and reduces the supply of oxygen to cells.

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