Aeromedical Factors

may progress over time require review by the FAA before a to pass between the membranes in the respiratory system. medical certificate may be issued. This decrease in number of oxygen molecules at sufficient pressure can lead to hypoxic hypoxia. The important thing to remember is that with very few exceptions, all disqualifying medical conditions may Dangers of Transporting Dry Ice be considered for special issuance. If you can present Sublimation is a process in which a substance transitions satisfactory medical documentation to the FAA that your from a solid to a gaseous state without passing through condition is stable, the chances are good that you will be an intermediate liquid state. Dry ice sublimates into large able to qualify for an Authorization. quantities of CO gas, which can rapidly displace oxygen- 2 containing air and potentially cause hypoxia via carbon Health and Physiological Factors dioxide intoxication. Case studies have shown that both illness Affecting Pilot Performance and death can be caused by occupational and/or unintentional exposure when transporting dry ice in small, confined A number of health factors and physiological effects can be spaces such as a flightdeck or airplane. Exposure to high linked to flying. Some are minor, while others are important concentration of CO gas may lead to increased respiration, enough to require special attention to ensure safety of flight. 2 tachycardia, cardiac arrhythmia, and unconsciousness. In some cases, physiological factors can lead to inflight Exposure to concentration of CO gas in excess of 10 percent emergencies. Some important medical factors that a pilot 2 may cause convulsions, coma, and/or death. should be aware of include hypoxia, hyperventilation, middle ear and sinus problems, spatial disorientation, motion The tendency of dry ice to rapidly sublimate also means that sickness, carbon monoxide (CO) poisoning, stress and without proper ventilation, it can rapidly pressurize. For fatigue, dehydration, and heatstroke. Other subjects include this reason, dry ice should never be placed inside a sealed the effects of alcohol and drugs, anxiety, and excess nitrogen transport container (i.e., leak-proof secondary container) in the blood after scuba diving. and must be placed within an outer shipping container or storage container that allows adequate ventilation to release Hypoxia the CO gas and avoid pressurization. Sealing dry ice within a Hypoxia means “reduced oxygen” or “not enough oxygen.” 2 leak-proof container may result in explosion of the container Although any tissue will die if deprived of oxygen long potentially leading to serious physical injury or death. enough, the greatest concern regarding hypoxia during flight is lack of oxygen to the brain, since it is particularly Hypemic Hypoxia vulnerable to oxygen deprivation. Any reduction in mental function while flying can result in life-threatening errors. Hypemic hypoxia occurs when the blood is not able to take Hypoxia can be caused by several factors, including an up and transport a sufficient amount of oxygen to the cells insufficient supply of oxygen, inadequate transportation of in the body. Hypemic means “not enough blood.” This type oxygen, or the inability of the body tissues to use oxygen. of hypoxia is a result of oxygen deficiency in the blood, The forms of hypoxia are based on their causes: rather than a lack of inhaled oxygen, and can be caused by a variety of factors. It may be due to reduced blood volume • Hypoxic hypoxia (from severe bleeding), or it may result from certain blood • Hypemic hypoxia diseases, such as anemia. More often, hypemic hypoxia • Stagnant hypoxia occurs because hemoglobin, the actual blood molecule that transports oxygen, is chemically unable to bind oxygen • Histotoxic hypoxia molecules. The most common form of hypemic hypoxia is CO poisoning. This is explained in greater detail later in this Hypoxic Hypoxia chapter. Hypemic hypoxia can also be caused by the loss Hypoxic hypoxia is a result of insufficient oxygen available of blood due to blood donation. Blood volume can require to the body as a whole. A blocked airway and drowning several weeks to return to normal following a donation. are obvious examples of how the lungs can be deprived of Although the effects of the blood loss are slight at ground oxygen, but the reduction in partial pressure of oxygen at high level, there are risks when flying during this time. altitude is an appropriate example for pilots. Although the percentage of oxygen in the atmosphere is constant, its partial Stagnant Hypoxia pressure decreases proportionately as atmospheric pressure Stagnant means “not flowing,” and stagnant hypoxia or decreases. As an aircraft ascends during flight, the percentage ischemia results when the oxygen-rich blood in the lungs of each gas in the atmosphere remains the same, but there are is not moving, for one reason or another, to the tissues that fewer molecules available at the pressure required for them 17-3