 For over 200 years, man has flown through the atmosphere. However, it has been proven physiologically that we are best suited to live in conditions from sea level to 10,000 feet. When humans expose themselves to altitudes above 10,000 feet, certain physiological changes occur. This program will focus on the different types of hypoxia and how it affects the overall body function. Hypoxia is a known cause or contributing factor in aviation incidents and accidents. When altitude increases, the pressure of oxygen decreases, reducing the amount of oxygen carried in the blood. The ability of hemoglobin to carry oxygen is called the blood oxygen saturation, which is normally 95 to 98 percent at sea level. A decrease in blood oxygen saturation is measurable as we ascend. Hypoxia is an oxygen deficiency in the blood and affects every cell, especially the brain and nervous system. There are four types of hypoxia. Let's examine each of them. Hypoxic hypoxia, also known as altitude hypoxia, is the most common form of hypoxia in aviation and occurs due to a drop in oxygen pressure at the lung level. Hypoxic hypoxia can be caused by a decrease in the pressure of oxygen in the inspired air that can result from altitude exposure, strangulation, or respiratory arrest. In the aviation environment, hypoxia can occur when flying an unpressurized aircraft above 10,000 feet. Other causes of altitude hypoxia can be linked to failure of the aircraft's oxygen systems or the improper use of that equipment and or failure of the pressurization system. Stagnant hypoxia occurs at the circulatory level. It's defined as a condition that interferes with the normal circulation of the blood arriving at the cells. Stagnant hypoxia can occur as a result of cardiac arrest, shock, exposure to cold, and sudden changes in posture such as standing up after a prolonged rest. Aerobatic and agricultural flying expose pilots to acceleration forces commonly called G-forces that can result in this type of hypoxia at the brain level. Hypemic hypoxia is caused by a reduction in the oxygen-carrying capacity of the blood and occurs at the blood level. Anemia, bleeding, and some prescription drugs can cause hypemic hypoxia. Carbon monoxide exposure due to smoking or cabin contamination with engine exhaust fumes can also cause this type of hypoxia. Histotoxic hypoxia occurs at the cell level. Histotoxic hypoxia interferes with the normal utilization of oxygen in the cells. Alcohol and drugs are two items that can bring about this condition. Individual response to hypoxia varies. Your hypoxia symptoms may develop so gradually that they are well established before you recognize them. Hypoxia symptoms are most noted at cabin altitudes above 10,000 feet. This program, coupled with a flight in an altitude chamber, will better train you to recognize your personal hypoxic symptoms. Hypoxia reactions can be classified into two types. Signs of hypoxia can be detected in an individual, by an observer, or other crew members. Symptoms of hypoxia are the sensations perceived by the crew member. Keep in mind that there are certain hypoxic reactions that can be classified as both signs and symptoms. Some common signs of hypoxia are an increase in depth and rate of breathing, cyanosis, a bluing effect of the skin most noticeable on the lips and the fingernail beds, delayed reaction time, poor judgment, loss of muscle coordination. Some of the common symptoms of hypoxia are air hunger, a feeling of not enough breathable air, feeling of apprehension or anxiety, mental confusion, fatigue, nausea, headache, dizziness, hot and cold flashes, tingling mainly in the extremities, visual impairment with respect to color vision, night vision, blurred and tunnel vision. There are some important points to remember concerning hypoxic signs and symptoms. They are as individual as the person experiencing them. They may appear in a different order and can vary in intensity. The rate of individual onset will vary day to day due to other physiological and psychological stressors. Preoccupation with flying duties could be enough of a distraction to allow hypoxia to progress beyond the point of self-help. Behavior changes such as euphoria or belligerence may manifest themselves as a sign and symptom. Personal signs and symptoms normally remain the same over the years. There is the possibility some major life changes can add or subtract particular symptoms. Once you learn to recognize your hypoxia symptoms, you can begin to take corrective actions. Initial recovery from hypoxia can occur in a matter of seconds, while full recovery takes three to five minutes. Effective performance time, EPT, and time of useful consciousness, TUC, are two interchangeable terms used to describe human tolerance to hypoxia. They refer to the amount of time elapsed from the interruption of oxygen supply or individual exposure to an oxygen poor environment to the time when such an individual is no longer capable of performing routine flying tasks or taking proper corrective action against hypoxia. This chart shows the average EPT time at various altitudes. These times are to be used as averages only and are based on a healthy individual in a controlled environment at rest. It is important to remember that a rapid decompression will shorten these times by as much as 50%. Factors that can affect EPT include the faster you ascend to altitude, either by rate of climb or a rapid decompression. Peak altitude, physical activity at altitude, fatigue, dehydration, hypoglycemia, low blood sugar level, alcohol, over-the-counter medication and prescription drugs, smoking. The best advice is to be aware of the limitations of the body to altitude and oxygen requirements in accordance with the Federal Aviation Regulations, FARs. The FAR states, no person may operate a civil aircraft of U.S. Registry, one at cabin pressure altitudes above 12,500 feet MSL, up to and including 14,000 feet MSL, unless the required minimum flight crew is provided with and uses supplemental oxygen for that part of the flight at those altitudes that is of more than 30 minutes duration. Two, at cabin pressure altitudes above 14,000 feet MSL, unless the required minimum flight crew is provided with and uses supplemental oxygen during the entire flight time at those altitudes. However, it is highly recommended that supplemental oxygen be used above 5,000 feet MSL during all night flights and above 10,000 feet MSL during all daytime flights. If at altitude you begin to experience hypoxia signs or symptoms, here's an airborne checklist. First, don your oxygen mask. Second, turn on the oxygen. Then, select the proper oxygen setting for altitude, if applicable. Third, make sure oxygen is being delivered. Check flow indicator. Fourth, make sure all connections are secure. Fifth, intentionally slow down your breathing rate to prevent hyperventilation. Sixth, descend to an altitude where supplemental oxygen is no longer required. Hypoxia is a constant danger. Through education and knowledge, pilots can take active steps toward prevention and protection. Currently, the FAA and several military training facilities provide physiological training. The training includes a simulated high altitude flight in a hypobaric or low pressure altitude chamber. The hypobaric chamber allows a participant to experience hypoxia in a controlled environment where you can learn to recognize your own personal signs and symptoms of hypoxia. Hypoxia is an oxygen deficiency in the blood and affects every body cell, especially the brain and nervous system. There are four types of hypoxia. Hypotic hypoxia, also known as altitude hypoxia, the most common form of hypoxia in aviation. It occurs at the lung level. Stagnant hypoxia occurs at the circulatory level. It's defined as a condition that interferes with the normal circulation of the blood arriving at the cells. Hypemic hypoxia is caused by a reduction in the oxygen carrying capacity of the blood and occurs at the blood level. Histotoxic hypoxia occurs at the cell level. Histotoxic hypoxia interferes with the normal utilization of oxygen in the cells. Hypoxia symptoms are most likely to occur at cabin altitudes above 10,000 feet MSL. Hypoxia reactions can be classified into two types. Signs of hypoxia can be detected in an individual by an observer or other crew members. Symptoms of hypoxia are the sensations perceived by the crew member. Effective performance time, EPT, and time of useful consciousness, TUC, are two interchangeable terms used to describe human tolerance to hypoxia. These terms refer to the amount of time elapsed from exposure to an oxygen poor environment to the time when an individual is no longer capable of performing routine flying tasks or taking proper corrective action against hypoxia. If at altitude you begin to experience hypoxia signs or symptoms, here's an airborne checklist. First, don your oxygen mask. Second, turn on the oxygen. Then select the proper oxygen setting for altitude, if applicable. Third, make sure oxygen is being delivered. Check flow indicator. Fourth, make sure all connections are secure. Fifth, intentionally slow down your breathing rate to prevent hyperventilation. Sixth, descend to an altitude where supplemental oxygen is no longer required.