Environmental and Health Factors  Affecting Pilot Performance Stagnant Hypoxia Hypoxia Histotoxic Hypoxia Symptoms of Hypoxia Hypoxic Hypoxia Hypemic Hypoxia most common cause of hypemic hypoxia is carbon monoxide  poisoning. Hypemic hypoxia can also be caused by the loss  of blood from a blood donation. While the volume of blood  is restored quickly following a donation, normal levels of  hemoglobin can require several weeks to return. Although  the effects of the blood loss are slight at ground level, there  are risks when flying during this time. A number of health factors and physiological effects can be  linked to flying. Some are minor, while others are important  enough to require special consideration to ensure safety of  flight. In some cases, physiological factors can lead to in- flight emergencies. Some important medical factors that a  pilot should be aware of include hypoxia, hyperventilation,  middle ear and sinus problems, motion sickness, stress and  fatigue, dehydration, and heatstroke. Other subjects include  the effects of alcohol and drugs, anxiety, and excess nitrogen  in the blood after scuba diving. Stagnant means “not flowing.” Stagnant hypoxia results  when the oxygen-rich blood in the lungs is not moving, for  one reason or another, to the tissues that need it. One form of  stagnant hypoxia is an arm or leg “going to sleep” because  the blood flow has accidentally been shut off. This kind of  hypoxia can also result from shock, the heart failing to pump  blood effectively, or a constricted artery. Cold temperatures  can also reduce circulation and decrease the blood supplied  to extremities.  Hypoxia means “reduced oxygen” or “not enough oxygen.”  Although any tissue will die if deprived of oxygen long  enough, the main concern is usually with getting enough  oxygen to the brain, since it is particularly vulnerable to  oxygen deprivation. Any reduction in mental function while  flying can result in life-threatening errors. Hypoxia can be  caused by several factors, including an insufficient supply of  oxygen, inadequate transportation of oxygen, or the inability  of the body tissues to use oxygen. Four forms of hypoxia  based on their causes are: hypoxic hypoxia, hypemic hypoxia,  stagnant hypoxia, and histotoxic hypoxia. The inability of the cells to effectively use oxygen is defined  as histotoxic hypoxia. “Histo” refers to tissues or cells, and  “toxic” means poison. In this case, plenty of oxygen is being  transported to the cells that need it, but they are unable to  make use of it. This impairment of cellular respiration can  be caused by alcohol and other drugs, such as narcotics and  poisons. Research has shown that drinking one ounce of  alcohol can equate to an additional 2,000 feet of physiological  altitude. There are other issues concerning the use of alcohol  in relation to flying in general; those will be discussed later  in this chapter. Hypoxic hypoxia is a result of insufficient oxygen available  to the body as a whole. A blocked airway and drowning are  obvious examples of how the lungs can be deprived of oxygen,  but the reduction in partial pressure of oxygen at high altitude  is an appropriate example for pilots. Although the percentage  of oxygen in the atmosphere is constant, its partial pressure  decreases proportionately as atmospheric pressure decreases.  As the aircraft ascends during flight, the percentage of each  gas in the atmosphere remains the same; however, there are  fewer molecules available at the pressure required for them  to pass between the membranes in the respiratory system.  This decrease in number of oxygen molecules at sufficient  pressure can lead to hypoxic hypoxia. High altitude flying can place a pilot in danger of becoming  hypoxic. Oxygen starvation causes the brain and other vital  organs to become impaired. One noteworthy attribute of  the onset of hypoxia is that the first symptoms are euphoria  and a carefree feeling. With increased oxygen starvation,  the extremities become less responsive and flying becomes  less coordinated. The symptoms of hypoxia vary with the  individual, but common symptoms include: Hypemic hypoxia occurs when the blood is not able to take  up and transport a sufficient amount of oxygen to the cells  in the body. Hypemic means “not enough blood.” This type  of hypoxia is a result of oxygen deficiency in the blood,  rather than a lack of inhaled oxygen, and can be caused by a  variety of factors. It may be because there is not enough blood  volume (due to severe bleeding), or may result from certain  blood diseases, such as anemia. More often it is because  hemoglobin, the actual blood molecule that transports  oxygen, is chemically unable to bind oxygen molecules. The  •  Lightheaded or dizzy sensation, •  Drowsiness, •  Visual impairment, •  Euphoria, •  Impaired judgment, •  Decreased reaction time, •  Headache, •  Cyanosis (blue fingernails and lips), 9-2