may progress over time require review by the FAA before a medical certificate may be issued. 

The important thing to remember is that with very few exceptions, all disqualifying medical conditions may be considered for special issuance. If you can present satisfactory medical documentation to the FAA that your condition is stable, the chances are good that you will be able to qualify for an Authorization. 

## Health and Physiological Factors Affecting Pilot Performance 

A number of health factors and physiological effects can be linked to flying. Some are minor, while others are important enough to require special attention to ensure safety of flight. In some cases, physiological factors can lead to inflight emergencies. Some important medical factors that a pilot should be aware of include hypoxia, hyperventilation, middle ear and sinus problems, spatial disorientation, motion sickness, carbon monoxide (CO) poisoning, 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. 

## Hypoxia 

Hypoxia means “reduced oxygen” or “not enough oxygen.” Although any tissue will die if deprived of oxygen long enough, the greatest concern regarding hypoxia during flight is lack of 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. The forms of hypoxia are based on their causes: 

• Hypoxic hypoxia 

• Hypemic hypoxia 

• Stagnant hypoxia 

• Histotoxic hypoxia 

## Hypoxic Hypoxia 

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 an aircraft ascends during flight, the percentage of each gas in the atmosphere remains the same, but 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. 

## Dangers of Transporting Dry Ice 

Sublimation is a process in which a substance transitions from a solid to a gaseous state without passing through an intermediate liquid state. Dry ice sublimates into large quantities of CO$_{2}$ gas, which can rapidly displace oxygen- containing air and potentially cause hypoxia via carbon dioxide intoxication. Case studies have shown that both illness and death can be caused by occupational and/or unintentional exposure when transporting dry ice in small, confined spaces such as a flightdeck or airplane. Exposure to high concentration of CO$_{2}$ gas may lead to increased respiration, tachycardia, cardiac arrhythmia, and unconsciousness. Exposure to concentration of CO$_{2}$ gas in excess of 10 percent may cause convulsions, coma, and/or death. 

The tendency of dry ice to rapidly sublimate also means that without proper ventilation, it can rapidly pressurize. For this reason, dry ice should never be placed inside a sealed transport container (i.e., leak-proof secondary container) and must be placed within an outer shipping container or storage container that allows adequate ventilation to release the CO$_{2}$ gas and avoid pressurization. Sealing dry ice within a leak-proof container may result in explosion of the container potentially leading to serious physical injury or death. 

## Hypemic Hypoxia 

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 due to reduced blood volume (from severe bleeding), or it may result from certain blood diseases, such as anemia. More often, hypemic hypoxia occurs because hemoglobin, the actual blood molecule that transports oxygen, is chemically unable to bind oxygen molecules. The most common form of hypemic hypoxia is CO poisoning. This is explained in greater detail later in this chapter. Hypemic hypoxia can also be caused by the loss of blood due to blood donation. Blood volume can require several weeks to return to normal following a donation. Although the effects of the blood loss are slight at ground level, there are risks when flying during this time. 

## Stagnant Hypoxia 

Stagnant means “not flowing,” and stagnant hypoxia or ischemia results when the oxygen-rich blood in the lungs is not moving, for one reason or another, to the tissues that 

