Aeromedical Factors

need it. An arm or leg “going to sleep” because the blood endurance or acclimatization. When flying at high altitudes, flow has accidentally been shut off is one form of stagnant it is paramount that oxygen be used to avoid the effects of hypoxia. This kind of hypoxia can also result from shock, hypoxia. The term “time of useful consciousness” describes the heart failing to pump blood effectively, or a constricted the maximum time the pilot has to make rational, life-saving artery. During flight, stagnant hypoxia can occur with decisions and carry them out at a given altitude without excessive acceleration of gravity (Gs). Cold temperatures supplemental oxygen. As altitude increases above 10,000 can also reduce circulation and decrease the blood supplied feet, the symptoms of hypoxia increase in severity, and the to extremities. time of useful consciousness rapidly decreases. [Figure 17-1] Since symptoms of hypoxia can be different for each Histotoxic Hypoxia individual, the ability to recognize hypoxia can be greatly The inability of the cells to effectively use oxygen is defined improved by experiencing and witnessing the effects of it as histotoxic hypoxia. “Histo” refers to tissues or cells, and during an altitude chamber “flight.” The Federal Aviation “toxic” means poisonous. In this case, enough oxygen is being Administration (FAA) provides this opportunity through transported to the cells that need it, but they are unable to make aviation physiology training, which is conducted at the FAA use of it. This impairment of cellular respiration can be caused CAMI in Oklahoma City, Oklahoma, and at many military by alcohol and other drugs, such as narcotics and poisons. facilities across the United States. For information about the Research has shown that drinking one ounce of alcohol can FAA’s one-day physiological training course with altitude equate to an additional 2,000 feet of physiological altitude. chamber and vertigo demonstrations, visit the FAA website at www.faa.gov. Symptoms of Hypoxia High-altitude flying can place a pilot in danger of becoming Hyperventilation hypoxic. Oxygen starvation causes the brain and other vital Hyperventilation is the excessive rate and depth of respiration organs to become impaired. The first symptoms of hypoxia leading to abnormal loss of carbon dioxide from the blood. can include euphoria and a carefree feeling. With increased This condition occurs more often among pilots than is oxygen starvation, the extremities become less responsive and generally recognized. It seldom incapacitates completely, but flying becomes less coordinated. The symptoms of hypoxia it causes disturbing symptoms that can alarm the uninformed vary with the individual, but common symptoms include: pilot. In such cases, increased breathing rate and anxiety further aggravate the problem. Hyperventilation can lead to • Cyanosis (blue fingernails and lips) unconsciousness due to the respiratory system’s overriding • Headache mechanism to regain control of breathing. • Decreased response to stimuli and increased reaction Pilots encountering an unexpected stressful situation may time subconsciously increase their breathing rate. If flying at • Impaired judgment higher altitudes, either with or without oxygen, a pilot may • Euphoria have a tendency to breathe more rapidly than normal, which often leads to hyperventilation. • Visual impairment • Drowsiness Since many of the symptoms of hyperventilation are similar • Lightheaded or dizzy sensation to those of hypoxia, it is important to correctly diagnose and treat the proper condition. If using supplemental oxygen, • Tingling in fingers and toes check the equipment and flow rate to ensure the symptoms are • Numbness Altitude Time of useful consciousness As hypoxia worsens, the field of vision begins to narrow and instrument interpretation can become difficult. Even with all 45,000 feet MSL 9 to 15 seconds these symptoms, the effects of hypoxia can cause a pilot to 40,000 feet MSL 15 to 20 seconds have a false sense of security and be deceived into believing 35,000 feet MSL 30 to 60 seconds everything is normal. 30,000 feet MSL 1 to 2 minutes 28,000 feet MSL 2½ to 3 minutes Treatment of Hypoxia 25,000 feet MSL 3 to 5 minutes Treatment for hypoxia includes flying at lower altitudes and/ 22,000 feet MSL 5 to 10 minutes or using supplemental oxygen. All pilots are susceptible 20,000 feet MSL 30 minutes or more to the effects of oxygen starvation, regardless of physical Figure 17-1. Time of useful consciousness. 17-4