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“Physiology of Flight: Flying and Hypoxia” Federal Aviation Administration, Civil Aerospace Medical Institute
NEW VERSION with improved video & sound: https://www.youtube.com/watch?v=m2Om53E0Plo
Public domain film from the National Archives, slightly cropped to remove uneven edges, with the aspect ratio corrected, and mild video noise reduction applied.
The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and equalization (the resulting sound, though not perfect, is far less noisy than the original).
Hypoxic hypoxia is a result of insufficient oxygen available to the lungs. A blocked airway, a drowning or a reduction in partial pressure (high altitude above 10,000 feet) are obvious examples of how lungs can be deprived of oxygen. Some medical examples are abnormal pulmonary function or respiratory obstruction, or a right-to-left shunt in the heart. Hypoxic hypoxia is seen in patients suffering from chronic obstructive pulmonary diseases (COPD), neuromuscular diseases or interstitial lung disease.
Some symptoms of hypoxic hypoxia are:
– Decreased reaction time
– Impaired judgment time
– Visual impairment
– Lightheaded or dizzy sensation
– Tingling in fingers and toes
Cerebral hypoxia is a reduced supply of oxygen to the brain. Cerebral anoxia is a complete lack of oxygen to the brain. There are four categories of cerebral hypoxia; in order of severity they are; diffuse cerebral hypoxia (DCH), focal cerebral ischemia, cerebral infarction, and global cerebral ischemia. Prolonged hypoxia induces neuronal cell death via apoptosis resulting in a hypoxic brain injury…
The brain requires approximately 3.3 ml of oxygen per 100 g of brain tissue per minute. Initially the body responds to lowered blood oxygen by redirecting blood to the brain and increasing cerebral blood flow. Blood flow may increase up to twice the normal flow but no more. If the increased blood flow is sufficient to supply the brain’s oxygen needs then no symptoms will result.
However, if blood flow cannot be increased or if doubled blood flow does not correct the problem, symptoms of cerebral hypoxia will begin to appear. Mild symptoms include difficulties with complex learning tasks and reductions in short-term memory. If oxygen deprivation continues, cognitive disturbances and decreased motor control will result. The skin may also appear bluish (cyanosis) and heart rate increases. Continued oxygen deprivation results in fainting, long term loss of consciousness, coma, seizures, cessation of brain stem reflexes, and brain death.
Objective measurements of the severity of cerebral hypoxia depend on the cause. Blood oxygen saturation may be used for hypoxic hypoxia, but is generally meaningless in other forms of hypoxia. In hypoxic hypoxia 95-100% saturation is considered normal. 91-94% is considered mild. 86-90% is considered moderate. Anything below 86% is considered severe.
It should be noted that cerebral hypoxia refers to oxygen levels in brain tissue, not blood. Blood oxygenation will usually appear normal in cases of hypemic, ischemic and hystoxic cerebral hypoxia. Even in hypoxic hypoxia blood measures are only an approximate guide — the oxygen level in the brain tissue will depend on how the body deals with the reduced oxygen content of the blood…
Altitude sickness—also known as acute mountain sickness (AMS), altitude illness, hypobaropathy, or soroche—is a pathological effect of high altitude on humans, caused by acute exposure to low partial pressure of oxygen at high altitude. It commonly occurs above 2,400 metres (8,000 feet). It presents as a collection of nonspecific symptoms, acquired at high altitude or in low air pressure, resembling a case of “flu, carbon monoxide poisoning, or a hangover”. It is hard to determine who will be affected by altitude sickness, as there are no specific factors that correlate with a susceptibility to altitude sickness. However, most people can ascend to 2,400 meters (8,000 ft) without difficulty….