Aviation Physiology

treatment procedures are;___________________________________________________ ________________________________________________________________________ 10. FAR 91.211 requires the use of supplemental oxygen for crew members in unpressurized aircraft at what altitude?_____________________________________ 11. Following SCUBA diving, flying should be delayed ____________ hours. 12. FAR 91.211 states that supplemental oxygen should be used during night flying at/and above what altitude?__________________________________________ 13. Pilots' disorientation is commonly called_____________________________ 14. What would you do to combat disorientation?____________________________ ________________________________________________________________________ 15. What question regarding aviation physiology do you want to ask?___________ ________________________________________________________________________ ________________________________________________________________________ PHYSICS OF THE ATMOSPHERE One of the primary problems of flight related to physiology has to do with the fact that the pressure of gases in the atmosphere change as we ascend and descend. It is essential that we have an understanding of the gases found in the atmosphere and their effects upon the body. Other factors, such as temperature change, also need to be understood so we can protect ourselves from these potential hazards. DEFINITION AND BENEFITS OF THE ATMOSPHERE The atmosphere is a gaseous envelope that covers the earth. The boundary of the atmosphere has been debated for years. While some scientists and physicists set the boundary at 35,000 miles, and a few biologists at 50,000 feet, most scientist, physicists, and meteorologists agree that a more practical boundary is around 1,000 nautical miles. Without the atmosphere there would be no life on earth. The atmosphere provides protection from harmful ultraviolet (UV) rays, cosmic rays, and meteorites. The atmosphere also protects the earth from extreme temperature variations. It supports animal and plant life through its gaseous content and provides rain to grow crops. COMPOSITION OF THE ATMOSPHERE The atmosphere is a mixture of gases. It is composed primarily of nitrogen (N2 ) and oxygen (O2 ). Because atmospheric gases other than oxygen and nitrogen are so low in percentage they will not be considered in this discussion. Therefore from this point on, we will consider the atmosphere to be composed of only oxygen and nitrogen. GAS PERCENTAGE USE BY BODY Nitrogen (N2 ) 80 Major portion of total atmospheric pressure or weight. Gas is inert in the body and is simply stored in tissues and cells. Oxygen (O2 ) 20 Essential for animal life. Supports body metabolism (the catabolic breakdown of glucose for the production of heat energy). Argon (A) trace Noble (no bodily function) Neon (Ne) trace Noble (no bodily function) Helium (He) trace Noble (no bodily function) Krypton (Kr) trace Noble (no bodily function) Xenon (Xe) trace Noble (no bodily function) Hydrogen (H2 ) trace (no bodily function) Carbon Dioxide trace End product of metabolism. (TABLE 1) METHODS OF EXPRESSING ATMOSPHERE 1-1 The gaseous atmosphere surrounding the earth is affected by the gravitational pull of the earth. Atmospheric pressure is the combined weight, or force, of all the atmospheric gases exerted at any given point. In 1924 the U.S. Weather Bureau in conjunction with the Bureau of Standards set forth the values used in measuring a standard day at sea level. This standard atmospheric pressure can be expressed in many different forms, depending on the method of measurement. The various forms of measurement are: INCREMENT STANDARD AT SEA LEVEL METHOD Pounds per Square Inch (PSI) 14.7 This is the weight of the atmosphere in pounds exerted on one square inch Inches of Mercury (in/Hg) 29.92 This is the height in inches that a column of mercury will rise in a vacuum tube when subjected to the weight of the atmosphere Millimeters of Mercury (mm/Hg) 760 This is the height in millimeters that a column of mercury will rise in a vacuum tube when subjected to the weight of the atmosphere (TABLE 2) ATMOSPHERIC PRESSURE As previously described, the combined weight, or force, of all gases in the atmosphere at any given point gives us our atmospheric pressure. As you ascend from sea level, the atmospheric pressure will correspondingly drop. As atmospheric pressure drops, the air becomes less dense. The primary reason for this phenomenon lies in the kinetic nature of atoms and molecules. Molecules, especially those of a gas, are highly kinetic, or, in a constant state of motion. As pressure around the molecules is reduced, the molecules will travel further apart. This explains why air becomes less dense as altitude increases, thus explaining the phenomenon of gas expansion. 1-2 PHYSICAL DIVISIONS OF THE ATMOSPHERE The envelope of air that surrounds the earth varies in pressure and temperature throughout its entire height. This is due to differential heating of the air by heat radiated from the earth. The rays from the sun strike the earth at a very low angle at the poles and almost vertically at the equator. Thus, more heat is radiated into the air at the equator than at the poles causing the air to rise higher which can vary the heights of the Troposphere division listed below. All the divisions of the atmosphere have their own special characteristics that separate them from the others. DIVISIONS ALTITUDES CHARACTERISTICS Troposhere Sea Level - 30,000 (poles) to 50,000 (equator) feet Variable temperature, water vapor, turbulence, storms, weather, temperature lapse rate Tropopause Separates Troposphere and Stratosphere Region of temperature stability that forms the boundary between the troposphere & stratosphere Stratosphere 50,000 feet - 50 miles Relatively constant temperature of -55 degrees Celsius, little water vapor, jet streams, little turbulence Ionosphere 50 miles - 600 miles Provides protection from UV rays, gets name from the ionized gas within this layer (UV rays strip electrons from gaseous molecules and creates ions) Exosphere 600 miles - 1000 miles Gradually becomes the vacuum of space, so little pressure and density that gaseous molecules rarely collide Space Over 1000 miles (TABLE 3) PHYSIOLOGICAL ZONES OF THE ATMOSPHERE 1-3 Another way to classify divisions of the atmosphere is from the point of view of the physiological effects on the human body. ZONES ALTITUDES PRESSURE CHARACTERISTICS Physiological Efficient Zone Sea Level - 12,500 feet 760 - 523 mm/Hg Generally, the body has adapted to operate in the lower regions of this zone. Minor trapped gas problems (ears, sinus, and GI tract.) occur in the lower region of this zone while shortness of breath, dizziness, headaches and fatigue in the upper region if exposure too long Physiological Deficient Zone 12,500 - 50,000 feet 523 - 87 mm/Hg The majority of flying is conducted in this zone. The lack of atmospheric pressure causes major physiological problems...hypoxia and decompression sickness Space Equivalent Zone 50,000 ft - 1000 miles 87 - 0 mm /Hg This environment is very hostile to humans. "Armstrong's line" is at 63,000 feet and any unprotected exposure above this level causes body fluids to boil. There is a need for a sealed cabin and thrusters on the air/space craft. (TABLE 4) PHYSICAL GAS LAWS A human clothed in everyday street apparel, rapidly exposed to an altitude of 45,000 feet, would become unconsciousness in 9 - 12 seconds with death shortly following. The dangerous element here is the reduced partial pressure of oxygen found at this altitude. Since air is a mixture of gases, it will behave as such and, therefore, is subject to the laws that govern all gases. The following laws explain the effects of reduced barometric pressure and its interplay on the human body. GAS LAW EXPLANATION AVIATION APPLICATION 1-4 Dalton's Law PT = P1 + P2+....PN The total pressure of a mixture of gas is equal to the sum of the partial pressure of each gas in the mixture HYPOXIA Explains how ascent to altitude reduces the total atmospheric pressure as well as each of the partial pressures associated with the total atmospheric pressure. Boyle's Law P1 = V2 P2 V1 A volume of a gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant TRAPPED GAS Explains how pressure change allows the gas to expand and contract in body cavities (ears, sinuses, and GI tract) with increasing and decreasing altitude. Henry's Law P1 = A1 P2 A2 The amount of gas dissolved in solution varies directly with the pressure of that gas over the solution. DECOMPRESSION SICKNESS Explains why nitrogen in the body comes out of solution forming bubbles that cause altitude decompression sickness. As altitude increases, pressure decreases and nitrogen will attempt to leave the body and equalize with the surrounding environment. If pressure change is too rapid, the excess nitrogen may form a bubble(s). Graham's Law Law of gaseous diffusion A gas will diffuse from an area of high concentration to an area of low concentration TRANSFER OF GAS IN BODY Explains the transfer of gases between the atmosphere and the lungs, the lungs and blood, and the blood and the cell Charles' Law P1T2 = P1T1 The pressure of a gas is directly proportional to its temperature. This gas law has no physiological bearing since that body temperature is a constant 98.6 degrees Fahrenheit. (TABLE 5) CONCLUSION 1-5 The atmosphere, through its life giving gases coupled with its ability to screen its occupants from the harmful properties of space (cosmic rays, x-rays, meteors, etc..), helps to ensure life on earth. Without an atmosphere, there would be no life as we know it. Additionally, the atmosphere, through aviation, provides career opportunity and a source for potential income. With all its benefits, the atmosphere can be your best friend, but, it can also be a formidable enemy. Humans are ground dwelling creatures that function best at low altitudes. Anytime humans find themselves at extreme altitude they are at a disadvantage. Precautions must be taken to curb the threats of hypoxia, decompression sickness, hypothermia, and spatial disorientation. Appreciate the atmosphere for what it does for you, but, respect it for what it can do to you. TABLE OF U.S. STANDARD ATMOSPHERE 1-6 1-7 FEET In. of Hg Mm of Hg PSI C F 0 2,000 4,000 6,000 8,000 10,000 29.92 27.82 25.84 23.98 22.22 20.58 760.0 706.7 656.3 609.1 564.6 522.7 14.69 13.66 12.69 11.91 11.77 10.10 15.0 11.0 7.1 3.1 -0.8 -4.8 59.0 51.8 44.7 37.6 30.5 23.4 12,000 14,000 16,000 18,000 20,000 19.03 17.57 16.21 14.94 13.75 483.4 446.5 412.0 379.7 349.5 9.34 8.63 7.96 7.34 6.76 -8.8 -12.7 -16.7 -20.7 -24.6 16.2 9.1 1.9 -5.1 -12.3 22,000 24,000 26,000 28,000 30,000 12.63 11.59 10.62 9.72 8.89 321.3 294.9 270.3 237.4 226.1 6.21 5.70 5.22 4.78 4.37 -28.6 -32.5 -36.5 -40.5 -44.4 -19.4 -26.5 -33.6 -40.7 -47.8 32,000 34,000 36,000 38,000 40,000 8.10 7.38 6.71 6.09 5.53 206.3 188.0 171.0 155.5 141.2 3.99 3.63 3.30 3.00 2.73 -48.4 -52.4 -55.0 -55.0 -55.0 -54.9 -62.0 -69.7 -69.7 -69.7 42,000 44,000 46,000 48,000 50,000 5.03 4.56 4.15 3.77 3.42 128.3 116.6 105.9 96.3 87.4 2.48 2.25 2.05 1.86 1.70 -55.0 -55.0 -55.0 -55.0 -55.0 -69.7 -69.7 -69.7 -69.7 -69.7 55,000 60,000 2.70 2.12 68.8 54.4 1.33 1.05 TEMPERATURE REMAINS CONSTANT 63,000 64,000 1.83 1.74 46.9 44.7 .907 .86 70,000 74,000 1.31 1.08 33.5 27.7 PSF 113.2 77.3 80,000 84,000 .82 .68 20.9 17.3 58.1 47.9 90,000 94,000 .51 .42 13.0 10.9 35.90 29.97 100,000 .32 8.0 22.30 Source: U.S. Standard Atmosphere - 1962 (TABLE 6) In. of Hg = Inches of Mercury C = Centigrade Mm of Hg = Millimeters of Mercury F = Fahrenheit PSI = Pounds per square inch PSF = Pounds per square foot RESPIRATION AND CIRCULATION When the human organism is exposed to the various stressors of aerial flight, (physical and psychological) all body functions are affected. However, the areas of the body that are affected most directly are the respiratory and circulatory systems. Therefore, it is important for the individual to be familiar with the actions and limitations of the human respiratory and circulatory systems. RESPIRATION A. The Concept of Respiration Respiration is defined as the exchange of gases between the organism and its environment. The more obvious features of this process are the absorption of oxygen from the atmosphere and the elimination of carbon dioxide from the body. The respiratory system is made up of the lungs, a series of conducting tubes called the bronchi, the trachea, the mouth, and the nose. Air first enters the nasal passages, or the mouth, where it is warmed, moisturized, and filtered. It passes down the throat to the trachea and then into the bronchial tubes and the lungs. Once inside the lungs, the large bronchial tubes will branch 16 times, while getting progressively smaller with each branch. Located at the very end of the 16th branch are the alveoli (air sacs). These air sacs are very small but are large in quantity. There are an estimated 300,000 air sacs total. Though each individual air sac is small, if every air sac was removed from your lungs, and placed on a flat surface in a rectangular fashion, it would occupy a space equal to half a tennis court. Each air sac is surrounded by a dense network of tiny capillaries. The capillaries are so dense that they actually resemble a sheet of blood around each air sac. Each air sac is constructed of a very thin membrane that is just one cell (1/50,000th of an inch) thick. This allows oxygen, as well as other gases, to diffuse across the membrane and into and out of the capillaries and blood. Cells in the body require oxygen for the burning of food material to produce energy. This process, called metabolism, converts glucose (blood sugar) and oxygen into carbon dioxide and water. The carbon dioxide produced from this reaction must be removed from the body. The lungs receive oxygen from the atmosphere which then diffuses into the blood. The blood, at the same time, releases carbon dioxide into the lungs to be exhaled. The oxygen is then transported by the blood to all cells that are low in oxygen. Once the oxygen is in the cell, and metabolism has taken place, carbon dioxide then leaves the cell for the blood. Once in the blood, the carbon dioxide is transported back to the lungs for exhalation. 2-1 B. Movement of Gases in the Respiratory System 1. External Respiration External respiration is the exchange of gasses between the lungs and the surrounding atmosphere. It is estimated that with every normal breath, you will inhale approximately 13 billion trillion oxygen molecules. This number is so large that it is difficult to grasp the sheer magnitude of the amount of molecules that are brought into the lungs. For that reason, the principle of partial pressure will be used. But, as mentioned before, partial pressure relies solely on the number of molecules available for gas exchange. The partial pressure of oxygen forces oxygen through the air sacs and into the blood (keep in mind that gaseous pressure in physiology depends entirely on concentration of molecules). The partial pressure of oxygen is approximately 20% of the total atmospheric pressure. If at sea level, this would be about 152mm of pressure (20% {oxygen percentage of the atmosphere} of the total atmospheric pressure {760mm}). When a breath is drawn into the lungs, one would expect the partial pressure of oxygen to remain at 152mm. However, the lungs contain other gases that exert a constant pressure (water vapor at 47mm and carbon dioxide at 40mm). These gases tend to displace a part of the oxygen as it reaches lung level. Therefore, these gases reduce the partial pressure of the oxygen at the air sac level to 102mm. Due to the function of Graham's Law which states: "An area of high gaseous pressure will exert force towards an area of low gaseous pressure", this will cause gases to move back and forth across a gas permeable membrane (such as the air sacs). The high partial pressure of oxygen (102mm) now diffuses through the air sac wall and into the blood. This in turn, raises the partial pressure oxygen in venous blood (blood that has left the cells and therefore is low in oxygen) from 40mm to 102mm. At the same time this is happening, the high pressure of carbon dioxide (approximately 47mm) in the blood 2-2 will cause some of the carbon dioxide to diffuse into the airsac where carbon dioxide pressure is a constant 40mm. The same principle that applies to external respiration also applies to internal respiration (the exchange of gases from the blood to the cells). The high partial pressure of oxygen in arterial blood, causes the oxygen to move from the blood into the cells. Due to metabolism, the high partial pressure of carbon dioxide in the cell will causes it to diffuse into the blood for transport to the lungs. CIRCULATION A. Function The circulatory system is concerned with the transportation of blood throughout the body. Blood carries food, oxygen, and water to the tissues and waste materials from the tissues. Blood has the additional function of maintaining body heat. B. Structure The segments of the body that comprise the circulatory system are the heart, arteries, veins, and capillaries. The heart is a pumping organ capable of forcing blood through the vessels as tissue requirements dictate. The interior of the heart is divided into the right and left halves and each half has two chambers. The arteries are the vessels that carry oxygenated blood away from the heart. The elastic walls of the arteries are muscular and strong, permitting the arteries to vary its carrying capacity. Small arteries connect larger arteries to capillaries. The capillaries 2-3 convey blood from the arteries to the veins. They are very small, thin walled, and usually form a network in the tissues in which the exchange of gases take place. The veins are the vessels that carry deoxygenated blood back to the heart. They have thinner walls and are less elastic than the corresponding sized arteries. When blood enters the veins from the capillaries it is under low pressure. Therefore, some method is necessary to get blood back to the heart, especially from the lower regions of the body. The muscles around the veins produce a milking action of the veins forcing blood toward the heart. Back flow of blood is prevented primarily by valves located in veins. C. Composition of the Blood Blood is made up of two parts, plasma and solids. Approximately 90% of plasma is water, in which many substances are dissolved or suspended. The solid part of the blood is made up of the white and red blood cells. White blood cells are composed largely of a substance that act as anti-bodies to assist in the fighting of disease and infections. The red blood cells are formed in the bone marrow and there are approximately 35 trillion total in the body. Each red blood cell is largely made up of a substance called hemoglobin. Each red blood cell contains approximately 250 million hemoglobin molecules. Each hemoglobin molecule within the red blood cell can carry 4 molecules of oxygen, so each red blood cell can carry approximately 1 billion oxygen molecules. The secret of hemoglobin is that it contains one atom of iron for every hemoglobin molecule. This gives the blood a chemical attraction for oxygen as well as its red color. The red blood cells carry 95% of all oxygen, while the remainder is suspended in plasma. It can be readily seen that a person who is anemic, for example, does not have enough functioning red blood cells and will begin to suffer the effect of lack of oxygen at a relatively low altitude. The blood of the average person contains about 15 grams of hemoglobin per 100 ml (milliliter) of blood. Each gram of hemoglobin is capable of combining with 1.34 ml of oxygen so the blood could contain 20 ml of oxygen per 100 ml of blood or 20 volumes percent if were completely saturated. Normal arterial saturation is about 95 - 97 % and the oxygen content is 19 volumes percent. The ability of hemoglobin to take up or release oxygen is not a linear function of the partial pressure. However, the relationship is well defined and is usually shown in the form of the oxygen dissociation curve. Venous or return blood has a normal oxygen tension of 40mm and contains 14 volume percent of oxygen, and is 65 - 75 % saturated. 2-4 2-5 CONCLUSION The respiratory and circulatory systems of the human body work very simplistic, yet, very efficiently. It gives the human body the capability to adjust and function in a variety of environments. But, the body has its limitations. If the change is too abrupt, then these systems can't adjust quickly enough and the body will suffer the affects. Know the body's limitation at altitude and take appropriate measures to compensate for those limitations. HYPOXIA This chapter deals with one of our most important physiological problems. One factor that tends to make hypoxia so dangerous is its insidious onset. Any aviator who flies above 12,000 feet in an unpressurized aircraft without supplemental oxygen is a potential hypoxia case. TYPES OF HYPOXIA Hypoxia is described as a state of oxygen deficiency in the blood, tissues, and cells sufficient to cause an impairment of body functions. Anything that impedes the arrival or utilization of oxygen to the cell, places the body in a hypoxic state. There are many conditions that can interrupt the normal flow of oxygen to the cells. The following table describes the various levels at which hypoxia can occur: Location of Impediment Common Name Explanation Lungs Hypoxic Hypoxia Any condition that interrupts the flow of O2 into the lungs. This is the type of hypoxia encountered at altitude due to the reduction of the partial pressure of O2. Blood Hypemic Hypoxia Any condition that interferes with the ability of the blood to carry oxygen. Anemia and carbon monoxide poisoning are two conditions that can keep the O2 from attaching to the hemoglobin within the red blood cell. Blood Transport Stagnant Hypoxia Any condition that interferes with the normal circulation of the blood arriving to the cells. Heart failure, shock, and positive G force along the Z axis will bring about this condition. Cell (TABLE 7) Histotoxic Hypoxia Any condition that interferes with the normal utilization of O2 in the cell. Alcohol, narcotics and cyanide all can interfere with the cell's ability to use the oxygen in support of metabolism. From the table, it is plain to see that any condition that interferes with oxygen's normal path to the cells will bring on hypoxia. While all cells require oxygen to function, some cells require more oxygen than others. Most cells have the ability to store an 3-1 emergency supply of O2. The central nervous system (made up of the brain and spinal cord) do not have this ability and also demand a great deal of oxygen (approximately 20% of all oxygen that you inhale feeds the brain). So, if the oxygen supply to the body is reduced, the brain will be one of the first organs to be affected. Another problem is that when the brain starts to feel the effects of hypoxia, the higher reasoning portion of the brain is the first affected. This means that judgment and cognitive skills diminish from the very start. HYPOXIA SIGNS AND SYMPTOMS Signs of hypoxia can be detected on an individual by an observer. Signs aren't a very effective tool for the victim to use to recognize hypoxia in themselves. Therefore, these signs should not be included with the personal symptoms one gets while experiencing hypoxia. Symptoms are the sensations a person can detect while in a hypoxic state. Personal symptoms of hypoxia are as individual as the person experiencing them. A group of people who are hypoxic will, a majority of the time, get the same symptoms. But, the symptoms will appear in a different order and in varying intensities. The greatest benefit in hypoxia symptoms is that the order and the intensity of the symptoms will usually remain constant over the years. This is a great gift, because a pilot will always know what to look for to keep hypoxia in check. Some of the more common signs and symptoms of hypoxia are: SIGNS SYMPTOMS Rapid Breathing Air Hunger Cyanosis (Bluing effect of the skin) Fatigue Poor Coordination Nausea Lethargy Headache Executing Poor Judgment Dizziness Hot & Cold flashes Tingling Visual Impairment Euphoria (TABLE 8) Of the listed symptoms, visual impairment is probably the least reliable. Your visual field will be affected, but, at such a slow rate that it could go unnoticed. Generally, symptoms will appear before unconsciousness occurs. Except for headache and nausea, there are no other uncomfortable symptoms. Of all the symptoms, euphoria (a false sense of well being) is probably the most dangerous. It puts the pilot in such a state of mind that individual well being, as well as that of the passengers, is a low priority. Another consideration is that, in most cases, hypoxia is very insidious. Any preoccupation with flying duties could be enough of a distraction to allow the hypoxia to progress beyond the point of self help. EFFECTIVE PERFORMANCE TIME / TIME OF USEFUL CONSCIOUSNESS 3-2 Effective Performance Time and the Time of Useful Consciousness are two broad and interchangeable terms used to describe the time/hypoxia limit. Time of Useful Consciousness (TUC) is described as the period of time from interruption of the oxygen supply or exposure to an oxygen-poor environment to the time when an individual is no longer capable of taking proper corrective and protective action. Effective Performance Time (EPT) is described as the amount of time an individual is able to perform flying duties efficiently in an environment with inadequate oxygen supply. The following table will show the TUC/EPT for various altitudes: ALTITUDE TUC/EPT 18,000 20 - 30 Min 22,000 10 Min 25,000 3 - 5 Min 28,000 2.5 - 3 Min 30,000 1 - 2 Min 35,000 .5 - 1 Min 40,000 15 - 20 Sec 43,000 9 - 12 Sec 50,000 9 - 12 Sec (TABLE 9) The above times are to be used as averages only and are based on an individual at rest. Physical activity at altitude, fatigue, self-imposed stress, and individual variation will make the times vary. Some of the more common factors that will cause your EPT/TUC to vary are: Rate of Ascent The faster you ascend to altitude, the shorter your EPT/TUC becomes. Physical Activity Any physical activity will reduce your EPT/TUC. For example, if you did 10 deep knee bends at 25,000 feet with your oxygen mask off, your EPT/TUC would be reduced by 50%. Fatigue If you enter the cock-pit in a fatigued state, you are less resistant to hypoxia. 3-3 Poor Nutrition The brain feeds exclusively from glucose (blood sugar), so, if your glucose is low, as in hypoglycemia, you're more prone to hypoxia. Alcohol Alcohol brings about its own form of hypoxia. When altitude is coupled alcohol, you are a strong candidate for a hypoxic episode. Over the Counter Medication Some drugs will cause cells not to utilize oxygen properly and therefore will make you less altitude resistant. (TABLE 10) One fact to keep in mind is that, with a rapid decompression to and above 30,000 feet, the average EPT/TUC will be reduced from 1/3 to 1/2 of its original value. This is due to a phenomenon known as reverse diffusion or fulminating hypoxia. This phenomenon is where oxygen, due to the rapid expansion of gas during a decompression, is forced from the lungs and creates a very acute hypoxia that is immediate. PREVENTIVE MEASURES AGAINST HYPOXIA There are certain counter-measures pilots can use to prevent hypoxia. 1. Fly at an altitude where oxygen is not required 2. Fly in a pressurized cabin 3. Fly in accordance with FARs (in reference to the use of supplemental oxygen) 12,500 - 14,000 feet for not more than 30 mins. NOTE CAMI recommends that on any unpressurized flight to or above 10,000 feet, supplemental oxygen should be used. TREATMENT FOR HYPOXIA Hypoxia, under most situations, will be insidious in its onset; thus, its dangerous nature. Fortunately, once the hypoxia is detected and 100% oxygen is administered, recovery is usually only a matter of seconds. Because of the rapid breathing associated with hypoxia, you must slow your breathing rate to prevent hyperventilation. 3-4 CONCLUSION Hypoxia is a constant danger. Many people suffer from ground level hypoxia before they even step inside the aircraft. The insidious nature of hypoxia is its true danger. You must always be on the look-out for hypoxia symptoms. Once hypoxia is recognized, recovery is only seconds away. Know your symptoms. Know your oxygen system and be ready to battle this potential threat to safe flight. 3-5 3-6 3-1 OXYGEN REQUIREMENTS AIRCRAFT ALTITUDE in feet BAROM. PRESS mm Hg BODY H2O PRESS. mm Hg TRACH. PRESS mm Hg %O2 INSP. AIR TRACH. PRESS. pO2 AVEOLAR pCO2 / pO2 mm Hg %O2 SAT. Hb. % SUPPLEM. O2 REQUIR. INSP. AIR TRACH. PRESS. pO2 %O2 SAT. Hb. SEA LEVEL 760 47 713 .21 149 40 / 103 96% 21% 149mm 96% 5000 632 47 585 .21 122 38 / 78 94% 25% 149mm 96% 10,000 523 47 476 .21 100 36 / 61 90% 31% 149mm 96% 15,000 429 47 382 .21 80 33 / 46 70% 40% 149mm 96% 20,000 349 47 302 .21 63 30 / 33 62% 49% 149mm 96% 25,000 282 47 235 .21 49 63% 149mm 96% TOTALLY INADEQUATE FOR METABOLIC REQUIREMENT 30,000 225 47 178 100% 37 40 / 103 96% 84% 149mm 96% 35,000 179 47 132 100% 28 39 / 93 95% 100% 132mm 95% 40,000 141 47 94 100% 20 35 / 59 87% 100% 94mm 87% PRESSURE/DILUTER DEMAND OXYGEN EQUIPMENT 40,000 141 47 94 .21 (x 1.00) (+ 8mm Hg) 20 94 102 INADEQUATE 35 / 59 36 / 66 87% 92% 100% 100% + PP 94mm 102mm 87% 92% 42,000 128 47 81 .21 (x 1.00) (+ 16mm Hg) 17 81 97 INADEQUATE 33 / 48 36 / 61 71% 90% 100% 100% + PP 81mm 97mm 90% 45,000 111 47 64 .21 (x 1.00) (+ 33mm Hg) 13 64 97 INADEQUATE 30 / 34 36 / 61 62% 90% 100% 100% + PP 64mm 97mm 90% 3-6 3-0 HYPERVENTILATION A normal breathing cycle in a healthy adult is considered to range from 12 - 16 breaths every minute. At this rate, a person is able to inhale a sufficient amount of oxygen to support the body's metabolic demand. When breathing at a rate faster than normal, you are considered to be in a state of hyperventilation. Physical Control of the Breathing Rate The breathing rate can be stimulated or slowed down through voluntary muscle control. This type of hyperventilation is not common. In the days when free diving was popular, the divers would purposely hyperventilate so that they could hold their breath longer than normal. This was a dangerous practice that often led to a diver passing out during the dive. Chemical Control of the Breathing Rate Breathing is primarily controlled through chemical means. Due to the process of metabolism, oxygen and glucose combine in the cells where the glucose releases heat and kinetic energy through a catabolic reaction. In this reaction, glucose and oxygen convert to carbon dioxide and water. 6O 2 + C6 H 12 O 6 6H 2 O + 6CO 2 Where 6O 2 is 6 oxygen molecule, combines with C6 H 12 O 6, which is glucose, will then result in the liberation of 6H 2 O, or, 6 molecules of water and 6CO 2, which is 6 carbon dioxide molecules. This reaction takes place within every cell of the human body and is the basis of metabolism. About 7% of CO2 released from the cell will dissolve in simple solution (plasma) and will be circulated to the lungs in this fashion for exhalation. Around 23% combines with red blood cells and forms carbaminohemoglobin. Most of the CO2, approximately 70%, will be carried as bicarbonate ions and adheres to the following reaction ; H 2 O +CO 2 H 2 CO 3 H + + HCO 3 - Where H 2 CO 3 is carbonic acid, a hydrogen ion (H +) is taken from the carbonic acid and forms HCO 3 - (bicarbonate ion). As mentioned above, 70% of all CO2 will be carried in the blood in this fashion. Once the venous blood arrives at the air sac, the reaction will reverse, and CO2 and water vapor will be exhaled. 4 - 1 1. Oxygen or Carbon Dioxide? So, which gas controls your breathing rate, oxygen or carbon dioxide? Many of you, based on what you have read, would probably answer oxygen. But, the answer is carbon dioxide. The amount of CO2 liberated during metabolism dictates the amount of bicarbonate, and more importantly, the amount of H+ (hydrogen ions) in the blood. The hydrogen ion concentration in the blood is monitored by the chemoreceptors. The chemoreceptors lie in carotid and aortic bodies. Within these large arteries, the chemoreceptors respond to increasing and decreasing hydrogen ion concentrations. During exercise there is an increased liberation of carbon dioxide. There will be a corresponding increase in hydrogen ion content of the blood. As the chemoreceptors sense this increase, they send a message to the brain instructing it to stimulate the breathing rate. As breathing rate increases, two primary objectives are met. An increase in oxygen uptake to feed the muscles involved in the exercise and to decrease the amount of hydrogen ions, as well as a decrease in CO2 that built up in the blood as a result of the exercise. This system works very well during exercise. But, if breathing is stimulated voluntarily (as in blowing up a balloon) or involuntarily (as in a fear reaction) without an increase in activity level, this system could bring about unconsciousness. HYPERVENTILATION The hyperventilation that most folks are familiar with is the type that accompanies pain or injury, anxiety, and fear. In these situations a person's breathing is controlled emotionally instead of chemically. Due to the natural release of adrenaline, the breathing rate will increase while physical activity remains about normal. In this scenario, a person would begin to breathe rapidly. Since there is no increased activity, the oxygen and hydrogen ion levels of the blood are normal. As the rapid breathing continues, oxygen levels remain normal but the CO 2 levels and the hydrogen ion levels of the blood rapidly drop. This tends to shift the pH balance of the blood towards the alkaline side. The chemoreceptors sense the H+ ion drop and begin to react. The alkaline rich blood, if permitted to be left in the cells long enough, can start to do 4 - 2 cellular damage. The brain, in an attempt to defend its self against this pH level, will start to restrict the blood flow to the brain. The brain will go into a hypoxic state and if not reversed in a period of time, will cause unconsciousness. Once the victim is unconsciousness, the breathing rate will slow, and the hydrogen ion level will return to normal level and decrease blood pH. 1. Recognizing Hyperventilation A person hyperventilating will have some definite signs and symptoms; DIZZINESS Dizziness is self explanatory. It feels very similar to the type experienced during hypoxia. BLURRY VISION As the blood is slowly restricted to the brain, the eyes will also be affected. TINGLING The tingling experienced is due to the alkaline-high blood reacting with the sensitive nerves of the extremities. TWITCHING MUSCLES As the alkaline-high blood enters the muscle, the muscle will react by twitching. Muscles of the face and the forearms seem to be the most prone. TETANY (Muscle spasm) As the alkaline increases in the blood and the blood penetrates deep within the muscle, the muscle will progress from the twitch to an eventual muscle spasm. (TABLE 11) Because the symptoms of hyperventilation and hypoxia are so similar, recognition of hyperventilation must be absolute. To make a symptom determination, check your altitude, cabin altitude, and your oxygen equipment. TREATMENT FOR HYPERVENTILATION 4 - 3 The only treatment is to slow the rate and depth of breathing. This will have to be a conscious effort on your part. If you are at an altitude where you aren't certain whether it is hyperventilation or hypoxia...TREAT THEM THE SAME. Don the mask and slow your breathing rate. CONCLUSION Hyperventilation in aviation is not common. First time flyers (passengers and students) will be the ones most likley affected. If a person in your aircraft is hyperventillating, remember to treat the cause and not the symptoms. 4 - 4 4 - 5 TRAPPED GAS As you have learned in earlier chapters, gas readily expands with any decrease in pressure. Gas expands in accordance with Boyle's Law, which states: "A volume of a gas is inversely proportional to the pressure to which it is subjected, temperature remaining constant." From this law it is apparent that if you reduce the pressure, as in ascending to altitude, gases increase in volume and vice versa on descent. The human body has several cavities that contain varying amounts of gas. Most of these cavities have an opening that will allow the gas to enter and escape. If the opening is reduced in size or closed, then the gas is trapped. Once trapped, it is still subject to gas expansion and compression in accordance with Boyles Law. The result of having changes in gas volume within these cavities without equalization will usually be pain. BODY AREA PROBLEM PHASE OF FLIGHT PHYSIOLOGY MIDDLE EAR DESCENT On ascent, the air and pressure of expanding gases will escape via the eustachian tube. The base of each eustachian tube is collapsed which acts as a one-way valve to allow gases and liquids to escape and not travel up to the middle ear. On descent, the gas is naturally trapped. Because of the increasing pressure on descent, this pressure will need to be equalized or an ear block will result. SINUSES DESCENT or ASCENT (rare) The maxillary sinuses that sit under the cheekbones and the frontals that lie under the eyebrows have an unobstructed opening that will allow gas to enter and escape. In the event of an upper respiratory infection (URI), the openings will be swollen and possibly closed allowing no route for the gas and pressure to equalize, resulting in a sinus block. TEETH ASCENT A tooth block is very rare. They can occur if you have had recent filling of a cavity. If there is any airspace trapped between the filling and the pulp of the tooth, it will expand on ascent and cause a tooth block. 5-1 GASTRO-INTESTINAL ASCENT The gastro intestinal tract will always contain a varying amount of gas. This gas is usually a result of the digestion process and can escape by either flatulation or belching. If the gas expands, as in unpressurized flight to altitude, and is not allowed to escape, it could result in a possible syncope (fainting). LUNGS DECOMPRESSION Gas in the lungs will normally enter and escape via the trachea. The easiest way to trap gas within the lungs is through breath holding. This can be a real problem during a decompression. The gases within the lungs will expand rapidly and must escape. If the gases are held in, they could cause possible lung damage. (TABLE 12) These gases are forever present in the body and must be considerd for every flight, pressurized or not. The major problems with the ears and sinuses will usually occur from 6,000 feet and lower. This is where the pilot and crewmember are subjected to greatest rate of pressure change. Also, flying with an upper respiratory infection will also increase the chances of a sinus or ear block. The following table will give the recommended procedures for in-flight treatment of trapped gas emergencies. ALIMENT SYMPTOMS TREATMENT Ear Block Can start out as a full feeling that will progress to pain. Pain will increases with descent. Can also cause vertigo. - Level off from descent. - Try ear-clearing maneuvers such as valsalva, aviators jaw jut, yawn, or swallow. - Ascend and try ear-clearing again. - If there is no relief, land A.S.A.P. Sinus Block Intense pain under the cheekbones and in the upper teeth (maxillary). Intense pain under eyebrows and in corner of the eyes (frontal). - Level off from descent. - Try the valsalva maneuver. - Ascend and try sinus-clearing again. - If there is no relief, land A.S.A.P. G.I. Tract Progressively increasing pain in the abdominal area with a corresponding increase in altitude. - Try to pass the gas through flatulating or belching. - If there is no relief, immediate descent. Tooth Block A pain in a single tooth where the pain increases with a corresponding increase in altitude. - Level off from ascent - See a dentist. - If there is no relief, land A.S.A.P. (TABLE 13) CONCLUSION 5 - 2 5 - 3 Gases are forever present in the body. These gases act in accordance with the physical laws that govern them. Allowing the gas to escape and equalize with the surrounding environment alleviates the potential for problems. But, if the gas becomes trapped, and the escape route (individual opening for each area) is blocked, the resulting reaction tends to be very painful. When you fly take into account that these gases are present and ready to become a potential problem. ALTITUDE INDUCED DECOMPRESSION SICKNESS Most problems associated with flying at high altitude are caused by the drop in atmospheric pressure as one ascends. One of the more dangerous problems an aviator may face is the threat of decompression sickness (possible nitrogen bubbles in body fluids and tissues) at altitude. This problem is not a new one. The first cases of decompression sickness occurred with caisson workers (tunnelers) in the early 1800s. Though the problem of decompression sickness has been studied for nearly 200 years, still there is not a lot known about this potentially life threatening disorder. The patho- physiology of decompression sickness stems from gaseous bubbles (presumably nitrogen) forming and lodging in various tissues of the body. But first, we need to examine how these bubbles form. As mentioned earlier, the problem of decompression sickness stems from reduced barometric pressure at altitude. While at sea level, we are breathing air that is composed of 80% nitrogen. Nitrogen is a noble gas, and can not be metabolized in the human body. This nitrogen that we breathe is taken into the lungs at a pressure of 608mm Hg (80% of the total atmospheric pressure [760mm Hg] at sea level). The nitrogen is then distributed through out the body, via the circulatory system, and stored at a pressure of about 608mm. As long as you remain at sea level, the nitrogen pressure inside the body and outside of the body are in equilibrium. But, when atmospheric pressure is reduced, as in flying unpressurized at altitude, then the equilibrium is upset. This will cause the nitrogen to leave the body. If the pressure differential is not too great, and, the rate of ascent is slow enough, then the nitrogen will leave as a gas and you simply exhale it. But, if the gas leaves too quickly, and the tissues become super saturated with nitrogen, a bubble(s) may form. Decompression sickness (DCS) describes a condition characterized by a variety of symptoms resulting from exposure to low barometric pressures that cause inert gases (mainly nitrogen), normally dissolved in body fluids and tissues, to come out of physical solution and form bubbles. DCS can occur during exposure to altitude (altitude DCS) or during ascent from depth (mining or diving). The first documented cases of DCS (Caissons Disease) were reported in 1841 by a mining engineer who observed the occurrence of pain and muscle cramps among coal miners exposed to air-pressurized mine shafts designed to keep water out . The first description of a case resulting from diving activities while wearing a pressurized hard hat was reported in 1869. ALTITUDE DECOMPRESSION SICKNESS Altitude DCS became a commonly observed problem associated with high- altitude balloon and aircraft flights in the 1930s. In present-day aviation, technology allows civilian aircraft (commercial and private) to fly higher and faster than ever before. Though modern aircraft are safer and more reliable, occupants are still subject to the stresses of high altitude flight—and the unique problems that go with these lofty heights. A century and one-half after the first DCS case was described, our understanding of DCS has improved and a body of knowledge has accumulated; however, this problem is far 6-1 from being solved. Altitude DCS still represents a risk to the occupants of modern aircraft. Tiny bubbles According to Henry's Law, when the pressure of a gas over a liquid is decreased, the amount of gas dissolved in that liquid will also decrease. One of the best practical demonstrations of this law is offered by opening a soft drink. When the cap is removed from the bottle, gas is heard escaping, and bubbles can be seen forming in the soda. This is carbon dioxide gas coming out of solution as a result of sudden exposure to lower barometric pressure. Similarly, nitrogen is an inert gas normally stored throughout the human body (tissues and fluids) in physical solution. When the body is exposed to decreased barometric pressures (as in flying an unpressurized aircraft to altitude, or during a rapid decompression), the nitrogen dissolved in the body comes out of solution. If the nitrogen is forced to leave the solution too rapidly, bubbles form in different areas of the body, causing a variety of signs and symptoms. The most common symptom is joint pain which is known as "the bends." Trouble sites Although bubbles can form anywhere in the body, the most frequently targeted anatomic locations are the shoulders, elbows, knees, and ankles. Table 14 (page 32) lists the different DCS types with their corresponding bubble formation sites and their most common symptoms. "The bends" (joint pain) account for about 60 to 70% of all altitude DCS cases with the shoulder being the most common site. Neurologic manifestations are present in about 10 to 15% of all DCS cases with headache and visual disturbances being the most common symptoms. "The chokes" are very infrequent and occur in less than 2% of all DCS cases. Skin manifestations are present in about 10 to 15% of all DCS cases. MEDICAL TREATMENT Mild cases of "the bends" and skin bends (excluding mottled or marbled skin appearance) may disappear during descent from high altitude, but still require medical evaluation. If the signs and symptoms persist during descent or reappear at ground level, it is necessary to provide hyperbaric oxygen treatment immediately (100% oxygen delivered in a high-pressure chamber). Neurological DCS, "the chokes", and skin bends with mottled or marbled skin lesions (see Table 1) should always be treated with hyperbaric oxygenation. These conditions are very serious and potentially fatal if untreated. FACTS ABOUT BREATHING 100% OXYGEN 6-2 One of the most significant breakthroughs in altitude DCS research was the discovery that breathing 100% oxygen before exposure to a low barometric pressure (oxygen prebreathing), decreases the risk of developing altitude DCS. Oxygen prebreathing promotes the elimination (washout) of nitrogen from body tissues. Prebreathing 100% oxygen for 30 minutes prior to initiating ascent to altitude reduces the risk of altitude DCS for short exposures (10-30 min only) to altitudes between 18,000 and 43,000 ft. However, oxygen prebreathing has to be continued, without interruption, with inflight breathing 100% oxygen to provide effective protection against altitude DCS. Furthermore, it is very important to understand that breathing 100% oxygen only during flight (ascent, enroute, descent) does not decrease the risk of altitude DCS, and should not be used in lieu of oxygen prebreathing. Although 100% oxygen prebreathing is an effective method to provide individual protection against altitude DCS, it is not a logistically simple nor an inexpensive approach for the protection of civil aviation flyers (commercial or private). Therefore, at the present time it is only being used by military flight crews and astronauts for their protection during high altitude and space operations. PREDISPOSING FACTORS Altitude There is no specific altitude that can be considered an absolute altitude exposure threshold, below which it can be assured that no one will develop altitude DCS. However, there is very little evidence of altitude DCS occurring among healthy individuals at altitudes below 18,000 ft. who have not been SCUBA (Self Contained Underwater Breathing Apparatus) diving. Individual exposures to altitudes between 18,000 ft. and 25,000 ft. have shown a low occurrence of altitude DCS. Most cases of altitude DCS occur among individuals exposed to altitudes of 25,000 ft. or higher. A U.S. Air Force study of altitude DCS cases reported that only 13% occurred below 25,000 ft. The higher the altitude of exposure, the greater the risk of developing altitude DCS. It is important to clarify that, although exposures to incremental altitudes above 18,000 ft. show an incremental risk of altitude DCS, they do not show a direct relationship with the severity of the various types of DCS (see Table 1). Repetitive Exposures Repetitive exposures to altitudes above 18,000 ft. within a short period of time (few hrs) also increase the risk of developing altitude DCS. Rate of Ascent The faster the rate of ascent to altitude, the greater the risk of developing altitude DCS. An individual exposed to a rapid decompression (high rate of ascent) above 18,000 ft. has a greater risk of altitude DCS than being exposed to the same altitude but at a lower rate of ascent. 6-3 Time at Altitude The longer the duration of the exposure to altitudes of 18,000 ft. and above, the greater the risk of altitude DCS. Age There are some reports indicating a higher risk of DCS with increasing age. Previous Injury There is some indication that recent joint or limb injuries may predispose individuals to developing "the bends". Ambient Temperature There is some evidence suggesting that individual exposure to very cold ambient temperatures may increase the risk of altitude DCS. Body Type Typically, a person who has a high body fat content is at greater risk of altitude DCS. Due to poor blood supply, nitrogen is stored in greater amounts in fat tissues. Although fat represents only 15% of an adult normal body, it stores over half of the total amount of nitrogen (about 1 liter) normally dissolved in the body. Exercise When a person is physically active while flying at altitudes above 18,000 ft., there is greater risk of altitude DCS. Alcohol Consumption The after-effects of alcohol consumption, such as dehydration, increase the susceptibility to DCS. Scuba Diving Before Flying SCUBA diving requires breathing air under high pressure. Under these conditions, there is a significant increase in the amount of nitrogen dissolved in the body (body nitrogen saturation). The deeper the SCUBA dive, the greater the rate of body nitrogen saturation. Furthermore, SCUBA diving in high elevations (mountain lakes), at any given depth, results in greater body nitrogen saturation when compared to SCUBA diving at sea level at the same depth. Following SCUBA diving, if not enough time is 6-4 allowed to eliminate the excess nitrogen stored in the body, altitude DCS can occur during exposure to altitudes as low as 5,000 ft. or less. WHAT TO DO WHEN ALTITUDE DCS OCCURS • Put on your oxygen mask immediately and switch the regulator to 100% oxygen. • Begin an emergency descent and land as soon as possible. Even if the symptoms disappear during descent, you should still land and seek medical evaluation while continuing to breath oxygen. • If one of your symptoms is joint pain, keep the affected area still; do not try to work pain out by moving the joint around. • Upon landing, seek medical assistance from an FAA medical officer, aviation medical examiner, military flight surgeon, or a hyperbaric medicine specialist. Be aware that a physician not specialized in aviation or hyperbaric medicine may not be familiar with this type of medical problem. Therefore, be your own advocate. • Definitive medical treatment may involve the use of a hyperbaric chamber operated by specially trained personnel. • Delayed signs and symptoms of altitude DCS can occur after return to ground level whether or not they were present during flight. THINGS TO REMEMBER • Altitude DCS is a potential risk every time you fly in an unpressurized aircraft above 18,000 feet (at lower altitudes if you SCUBA dive prior to the flight). • Be familiar with the signs and symptoms of altitude DCS (see Table 14) and monitor all aircraft occupants, including yourself, any time you fly an unpressurized aircraft above 18,000 ft. • Avoid unnecessary strenuous physical activity prior to flying an unpressurized aircraft above 18,000 ft. and for 24 hrs. after the flight. • Even if you are flying a pressurized aircraft, altitude DCS can occur as a result of sudden loss of cabin pressure (inflight rapid decompression). • Following exposure to an inflight rapid decompression, do not fly for at least 24 hrs. In the meantime, remain vigilant for the possible onset of delayed symptoms or signs of altitude DCS. If you experience delayed symptoms or signs of altitude DCS, seek medical attention immediately. • Keep in mind that breathing 100% oxygen during flight (ascent, enroute, descent) without oxygen prebreathing prior to take off, does not prevent the occurrence of altitude DCS. • Do not ignore any symptoms or signs that go away during the descent. In fact, this could confirm that you are actually suffering altitude DCS. • Any case of altitude DCS should be medically evaluated as soon as possible, even if symptoms are mild or disappear on descent. • If there is any indication that you may have experienced altitude DCS, do not fly again until you are cleared to do so by an FAA medical officer, aviation medical examiner (AME), a military flight surgeon, or a hyperbaric medicine specialist. • Allow at least 24 hrs. to elapse between SCUBA diving and flying. 6-5 • Be prepared for a future emergency by familiarizing yourself with the availability of hyperbaric chambers in your area of operations. However, keep in mind that not all of the available hyperbaric treatment facilities have personnel qualified to handle altitude DCS emergencies. To obtain information on location of hyperbaric treatment facilities capable of handling altitude DCS emergencies, call the Diver's Alert Network at (919) 684-8111. DCS Type Bubble Location Signs & Symptoms (Clinical Manifestations) 6-6 6-7 BENDS Mostly large joints of the body (shoulders, elbows, wrists, hips, knees, ankles)  Localized deep pain, ranging from mild (a "niggle") to excruciating. Sometimes a dull ache, but rarely a sharp pain  Active or passive motion of the joint aggravates the pain  Pain can occur at altitude, during the descent, or many hours later NEUROLOGIC Brain Spinal Cord Peripheral Nerves  Confusion or memory loss  Headache  Spots in visual field (scotoma), tunnel vision, double vision (diplopia), or blurry vision  Unexplained extreme fatigue or behavior changes  Seizures, dizziness, vertigo, nausea, vomiting, and unconsciousness may occur  Abnormal sensations such as numbness, burning, stinging, and tingling around the lower chest and back  Symptoms may spread from the feet up and may be accompanied by ascending weakness or paralysis  Girdling abdominal or chest pain  Urinary and rectal incontinence  Abnormal sensations such as numbness, burning, stinging, and tingling (paresthesia)  Muscle weakness or twitching CHOKES Lungs  Burning deep chest pain (under the sternum)  Pain is aggravated by breathing  Shortness of breath (dyspnea)  Dry constant cough SKIN BENDS (TABLE 14) Skin  Itching usually around the ears, face, neck, arms, and upper torso  Sensation of tiny insects crawling over skin (formication)  Mottled or marbled skin usually around the shoulders, upper chest and abdomen, accompanied by itching  Swelling of the skin, accompanied by tiny scar- like skin depressions (pitting edema) PRESSURIZATION AND DECOMPRESSION The dangers associated with high altitude flying (hypoxia, decompression sickness, ect..) can be avoided by flying in a pressurized cabin. Most modern day aircraft can cruise at altitudes between 25,000 - 51,000 feet and yet keep the cabin at a comfortable altitude of 6,500 - 8,000 feet. With the cabin at such a tolerable altitude, crew and passengers can benefit from these advantages: Oxygen mask may not need to be worn while pressurized Decompression Sickness risk is minimal Less noise and vibration during flight Better control of heat and ventilation Less ear & sinus blockage: Descent is around 300 - 500 feet per minute The basic mechanics of a pressurization system are fairly simple. Ambient air is introduced into a compressor. Once the air is compressed, it heats up very rapidly and therefore must be cooled. The air is then introduced into the cabin. By use of over-flow valves, the air comes in quicker than it leaves, and this creates a high pressure environment. Pressurization systems aboard various aircraft will use one of three different pressurization schedules: 7-1 ISOBARIC Most commonly used. Cabin altitude is preset and remains there through out the flight ISOBARIC DIFFERENTIAL Used mainly in military fighters. Cabin altitude remains constant until a certain cruise altitude is reached where it maintains a constant pressure differential. SEALED CABIN The craft carries its own supply of gases to create the pressure environment. Used only for space flights. (TABLE 15) Even though there are numerous advantages to pressurized flight, there will always be one major disadvantage...possible loss of pressurization. The FAA currently recognizes three different types of decompressions; SLOW DECOMPRESSION Total loss of cabin pressurization in > 10 seconds RAPID DECOMPRESSION Total loss of cabin pressurization in 1 - 10 seconds EXPLOSIVE DECOMPRESSION Total loss of cabin pressurization in < 1 second (W/ 10 psi pressure change) (TABLE 16) From the table above, it is obvious that the major factor that separates the three types is time. There are also factors that dictate how fast an aircraft will decompress with any given scenario. These factors are: SIZE OF OPENING With all other factors equal, the larger the opening, the faster the pressure will travel out of the aircraft. SIZE OF CABIN With all other factors equal, the smaller the cabin the faster the pressure will depart. PRESSURE DIFFERENTIAL With all other factors equal, greater pressure differential = slower decompression. PRESSURE RATIO When cabin pressurization is lost, aircraft compressors will continue to operate. The rate at which the compressed air comes in dictates how fast pressure is lost. 7-2 ALTITUDE Higher altitude results in a faster decompression due to less resistance to the air leaving the aircraft. (TABLE 17) The faster pressurization is lost, the more detrimental the decompression becomes. Research has shown that effective performance time (EPT) can be cut by as much as 50% in a decompression to and above 30,000 feet. When an aircraft is cruising at 40,000 feet the crew has only seconds to take corrective action. Also, research indicates that the maximum safe altitude an aircraft can decompress and have the crew remain conscious (regardless of having an oxygen mask on) is 48,000 feet. From the previous statements , the importance of recognizing and taking immediate actions for a decompression is apparent. Here are some common phenomena that occur during a decompression; NOISE Noise can come from a leaky door seal, a window departing, a breech of structural integrity or from the aircraft's alarm system. FOG On smaller airframes (Lears, Citations, Falcons) the fog could fill the aircraft. On larger aircraft, it stays near the floor. FLYING DEBRIS/ DUST & DIRT If there is a large opening, anything not secured down will move towards the opening. These items could cause injuries. WIND BLAST As the aircraft looses pressure, it will be felt by crew and passengers as wind blast. COOLER TEMPERATURES When the pressure (air) departs the cabin, the temperature will drop. GAS EXPANSION As the gas expands w/ decreasing pressure, it will be most noticeable in the ears and G.I. tract of the body. (TABLE 18) These decompression phenomena are very common to Rapid and Explosive decompressions. But, during a slow decompression, none of the above listed signs may be present. For this reason, it is felt that the slow decompression is the most dangerous, and the aviator must always be on guard against this insidious threat. Recognition and the immediate execution of emergency procedures for decompression are the most important factors that dictate crew survivability. The common emergency procedures are: 7-3 7-4 DON MASK Don mask in 5 seconds or less. Check for flow. DESCEND Preferably below 10,000 feet. LAND A.S.A.P At nearest suitable installation where appropriate medical.help can be found. (TABLE 19) The decompression you will undergo in CAMI's altitude chamber will let you experience all the signs and symptoms while in a safe training environment. This awarness allows you the luxury of knowing what this potential hazard looks and feels like. Reducing the recognition time, this will allow you to don the mask quicker and initiate descent sooner than a pilot who's trying to second guess what's happening. CONCLUSION Pressurizing the cabin of an aircraft is a convenient means to escape the hazards of high altitude flight. But, there is one overriding factor that must always be kept in mind; at anytime you may loose that pressurization. When a cabin decompression occurs, the hazards of high altitude flight (hypoxia, decompression sickness, and hypothermia) are immediately brought into the cabin with you. The danger of slow decompressions must be emphasized for they can sneak-up on you and rob you of your judgment or even your consciousness. Always be on the lookout for the signs and symptoms of decompression and then take immediate corrective action. OXYGEN EQUIPMENT The development of oxygen equipment has necessarily paralleled progress in aircraft performance. Without protection from the physiological problems at altitude the human becomes the limitation on how fast, how high, and how well an aircraft can perform. Oxygen equipment is just one area of development that has enabled us to fly in the hostile environment above 12,000 feet. In this chapter you will learn the basic principles of oxygen equipment. Emphasis will be placed on the oxygen equipment currently being used. The proper and effective use of oxygen equipment will be stressed and will include the methods of checking the equipment prior to and in flight. The opportunity to use and become familiar with this equipment will be afforded you during the chamber flight phase of your training. DESIGN In general, an oxygen system consists of the following components: a. Containers for storing the oxygen b. Tubing to conduct the oxygen from the supply source to a metering device. c. The metering device or regulator that controls the percentage of the oxygen to the user. d. An oxygen mask to provide oxygen to the user. OXYGEN STORAGE Aircraft operators who routinely fly either pressurized or unpressurized at altitudes in excess of 10,000 feet commonly employ a fixed oxygen installation. This consists of containers affixed within the aircraft and serviced through and exterior fuselage valve. Light aircraft operators who normally fly below 10,000 feet often prefer to use portable oxygen equipment consisting of a container, regulator, mask outlet, pressure gauge, etc., as an integral unit that may be taken aboard the aircraft each time a flight is contemplated at altitudes above 10,000 feet. Portable equipment, in order to avoid weight and bulk problems, is limited in oxygen supply duration. Typical breathing time for four people at 18,000 feet is in the range of 1-1/2 hours using a 22 cubic foot container. Fixed oxygen installations usually offer much longer duration time. Actual times will depend upon size of oxygen containers in the system, and the number of people using the system. OXYGEN STORAGE METHODS 8-1 Gaseous oxygen is stored in containers at low pressure (400-450 psi) and high pressure (1800-2200 psi). The high pressure system is used very extensively in general and commercial aviation. The latest developments in oxygen systems for aircraft make use of chemical action and are termed solid state oxygen systems. Solid state oxygen has come into its own through its use in new jumbo jet transports. It has weight, duration, and storage advantages not found in other oxygen systems currently in use. 1. AVIATORS BREATHING OXYGEN Aviators gaseous oxygen is designated Grade A, Type I Oxygen, Military Specifications MIL-0-27210D. It must meet a minimum purity requirement, excluding moisture content, of 99.5 % by volume and may not contain more than 0.005 mg of water vapor per liter at 760 mm Hg and 68 degrees F. (20 degrees C.). It must be odorless and free from contaminants, including drying agents. Do not confuse aviators breathing oxygen with "technical" oxygen or "medical" oxygen. OXYGEN STORAGE SYSTEMS Low pressure gaseous oxygen has a pressure range of 400 - 450 PSI. Cylinder Types and Capacities Internal Volume (Cu inch) Length (inches) Diameter (inches) Available Oxygen (Cu foot) 280 14.5 5.75 3.8 280 15 5.75 3.8 500 23.5 5.75 6 1,000 18 10 13.8 1,000 44.5 5.75 13.8 2,100 24.5 12.5 29 18,000 49.5 24.5 248 (TABLE 20) High pressure gaseous oxygen - pressure range 1800 - 2200 PSI Cylinder Types and Capacities 8-2 Internal Volume (Cu in) Length (inches) Diameter (inches) Available Oxygen (Cu ft) 205 14 5.34 13.7 295 18.5 5.34 19.6 386 15.37 6.92 25.6 514 19.25 6.92 34.2 646 23.5 6.92 42.9 (TABLE 21) REGULATORS AND MASKS A. Continuous Flow The continuous flow oxygen regulator provides a flow of 100% oxygen. The rate of flow is usually measured in liters per minute. Flow rate may be controlled by turning a valve. Several regulators are offered that employ an altitude sensing aneroid to change the flow rate automatically. Continuous flow masks use an oronasal face piece to receive the oxygen flow. The face piece does not usually have an air tight or oxygen tight face seal. This permits the user to exhale around the face piece or through small face piece ports or openings designed to dilute the oxygen with ambient air. Continuous flow masks in use today make use of a rebreather bag. This bag is attached to the mask and enables the wearer to reuse a part of the exhaled oxygen. Usually, there is a device in the oxygen hose, which enables the wearer to see that oxygen is flowing through the system. B. Demand and Pressure Demand The demand regulator, as the name implies, operates to furnish oxygen only when the user inhales or demands it. A lever may also be employed to enable the regulator to automatically give either a mixture of cabin air and oxygen or 100% oxygen. This is referred to as the automix lever. The regulator is set up to give varying amounts of oxygen to the user depending upon the altitude attained. The demand mask is designed to accommodate an air tight and oxygen tight seal to the face. This mask is expected to retain all of the oxygen inhaled into the mask by the user and not be diluted by entry of outside air. The demand regulator and mask provide a higher altitude capability than most continuous flow systems. They may be safely used to altitudes of 40,000 feet. 8-3 Pressure demand regulators are designed to furnish oxygen on inhalation either as a mixture of air and oxygen or 100% oxygen. This regulator also provides a positive pressure application of oxygen to the mask face piece enabling the users' lungs to be pressurized with oxygen. This is of great benefit at extreme altitudes, such as 40,000 feet or higher. The oxygen pressure flow may be either manually controlled or function automatically on some regulators at a certain altitude through aneroid action. The pressure demand masks are designed to create an air tight and oxygen tight seal. The inhalation and exhalation valves are specially designed to permit oxygen pressure build up within the mask face piece and thus supply oxygen under pressure to the lungs. It is essential that demand and pressure demand masks be properly suspended by an adequate head harness and that the masks be afforded tension adjustments for the user to obtain a leak proof seal to the face. The higher you fly, the more critical this adjustment becomes. PRE-FLIGHT OXYGEN EQUIPMENT CHECK Prior to flight a person should locate the oxygen mask, practice donning it, and adjust the head harness to fit: locate and check thefunction of oxygen pressure gauges, flow indicators and connections: and check the quantity of oxygen in the system. The mask should be donned and the oxygen system should be checked for function. A physical check of the mask and tubing to spot any cracks, tears, or deterioration would also be indicated. If a person is using a mask connection to an individual regulator, check for regulator condition and lever or valve positioning as required by that particular system. GENERAL RULES FOR OXYGEN SAFETY Do not inspect oxygen equipment with greasy hands. Do not permit accumulation of oily waste or residue in the vicinity of the oxygen system. Do not use surplus oxygen equipment unless it is inspected by a certified FAA inspection station and is approved for use. Some military components use oxygen containers stressed for a pressure of 450 PSI (low pressure). Needless to say, a hazard exists if a person attempts to put 1800-2200 PSI oxygen pressure in this type container. Make sure that high pressure oxygen containers are marked to indicate 1800 PSI before attempting to fill the container to this pressure. Most individuals do not possess the equipment necessary to fill an aircraft oxygen container from another source of high pressure oxygen. It is recommended that oxygen system servicing be done at FAA certified stations such as are located at some fixed base operations, terminal complexes, etc. 8-4 8-5 After any use of oxygen, give careful attention to ascertain that all flow is shut off before lighting cigarettes, etc. Oxygen systems must be engineered to protect the individual to the maximum anticipated flight altitude of the aircraft. Before purchasing any oxygen equipment, it is recommended that you inform the distributor on such factors as peak altitude to be flown, number of persons who will use the oxygen system, expected oxygen breathing duration, range of the aircraft, and any other information you think will be helpful in designing a proper oxygen system. Do not make any modification to the system without first consulting the supplier or distributor. Do not place portable oxygen containers in the aircraft unless you fasten them securely to insure against displacement in the event of turbulence, unusual attitudes, etc. ALTITUDE CHAMBER FLIGHT Altitude chambers have proven to be very valuable training devices. They give aviators the chance to experience many of the hazards of high altitude flight in a controlled and safe environment. Some people look at altitude chamber flights as "practice bleeding" and unnecessary for teaching and demonstrating the potential hazards that face all pilots and crewmembers. It is strongly felt by the majority of Physiologists, AMEs and most pilots that the best way to learn about altitude effects is by experience. Altitude chambers allow you to experience unpressurized flight: gas expansion, rapid decompression, hypoxia, and the use of oxygen equipment. THEORY OF OPERATION Altitude chambers work in accordance with a gas law that states "When you remove the gas you will also remove the pressure of the gas". The altitude chamber employes a vacuum pump to remove gas/pressure from the chamber. As the pressure is removed, it simulates the corresponding pressure of a particular altitude. This creates a low pressure in the chamber, and coincides with the low pressure one experiences during unpressurized flight. Dr. Paul Bert and the first altitude chamber (circa 1874) HISTORY OF ALTITUDE CHAMBERS 9-1 The first altitude chamber flight for training purposes took place in March 1874. Dr. Paul Bert of France (noted in history as the first practicing flight surgeon) used a diving bell and a steam driven vacuum pump to train two young men on the hazards of high altitude balloon flights. Through the years, the military has conducted altitude chamber training for all crewmembers flying on military aircraft. The FAA began altitude chamber flights for civilian pilots and crewmembers in 1962. The FAA has enjoyed a very safe history with its chamber flight profiles; undesirable reactions have occurred in just 9.9% of all chamber participants. And most of those reactions were mild (chiefly, earblocks and sinus pain). (CAMIs new altitude chamber delivered in 1998. The only chamber to date that meets the P.V.H.O. standards) (Control Console with manual and computer controls) THE FAA/CAMI ALTITUDE CHAMBER FLIGHT PROFILE 9-2 The chamber profile currently used by CAMI (Civil Aeromedical Institute) was instituted in 1973. It has proven to be a very effective and comfortable flight profile when time, safety, and training effectiveness are considered. The flight profile will consist of: 1. Pre-Flight Briefing This will normally take place in the classroom and is intended to familiarize the student with the flight profile and safety aspects of the altitude chamber 2. Oxygen Equipment Lab This will occur inside the altitude chamber and is intended to familiarize the students with the oxygen equipment they will be using during the flight. Correct donning procedures, mask fitting, and regulator function will be demonstrated by each student. 3. Ear & Sinus Check At this point, the chamber door will be closed and the chamber will ascend at 3,000 feet per minute to a simulated altitude of 6,000 feet. After ensuring the comfort and condition of each student, the chamber will descend at 3,000 feet per minute to 2,000 feet where, once again, the instructor will assess the condition of each student. 4. Rapid Decompression The chamber will ascend to 8,000 feet at 3,000 feet per minute. From 8,000 feet, the chamber will rapidly climb to 18,000 feet in 8 - 10 seconds. This is known as a rapid decompression. 5. Ascent to 25,000 feet The chamber will continue to ascend at 3,000 feet per minute to 25,000 feet for the next demonstration. 6. Hypoxia Demonstration At 25,000 feet, the chamber is at the peak altitude of the flight profile and this is where students will have a chance to experience their personal symptoms of hypoxia. There will be a five minute limit for students to acquire their symptoms. 9-3 9-4 7. Descent to Ground The chamber will descend to ground level at 3,000 feet per minute. (TABLE 22) SPATIAL DISORIENTATION SENSORY ILLUSIONS OF FLIGHT VERTIGO The terms listed in our title are often used interchangeably even though their exact meanings differ somewhat: SENSORY ILLUSION A false or misinterpreted sensory impression; a false interpretation of a real sensory image. VERTIGO A hallucination of movement. A sensation of rotary motion of the external world or of the individual. SPATIAL DISORIENTATION Loss of proper bearings; state of mental confusion as to position, location, or movement relative to the position of the earth. (TABLE 23) Sensory receptors in various parts of the body provide the brain with information relative to your position in your environment. The eyes, vestibular apparatus, and muscle senses practically tell you which way is up. In flying, many conditions you encounter can cause conflicts, or illusions, in these sensory functions. Cockpit confusion might be another term for disorientation, since the information from your senses and from your instruments may be contradictory. To understand the functions of the organs of equilibrium and how interpretations of these senses may lead to sensory illusions and spatial disorientation is a complex but rewarding undertaking. SENSORY SYSTEMS INVOLVED IN EQUILIBRIUM The sensory organs of the body associated primarily with maintaing body equilibrium are the eyes, semicircular canals (vestibular apparatus), and the skeletal muscles (proprioceptors). A. THE EYES The eye acts as the receptor organ for visual sensations. These sensations establish impulses in the cone and rod cells and the impulses travel the optic nerve to the brain for interpretation. The eye is very reliable for orientation, provided adequate reference points are available. When flying, however, you are at a disadvantage when trying to interpret visual cues. An object seen from the air often looks quite different than objects 10-1 seen from the ground. Also, you are used to having the ground extend to the horizon. In the air you lack the visual cues that a continuous background provides for recognizing objects and deciding their size and distance. A very common mistake is in interpreting the lights that you see at night. Pilots can become confused about the relationship between their own motion and the false motion of fixed lights on the ground. Thus, a pilot may decide that a fixed light on the ground is another airplane traveling in the opposite direction. If you cannot see the horizon, you may mistakenly choose some other line as a reference and, for example, may fly parallel to a tilted cloud bank instead of the ground. Consider what happens when no clouds are present and the horizon is obscured by haze or adverse lighting conditions. In such a situation you are apt to be completely without reference, which amounts to flying blind. In Alaska and other similar areas, this problem is particularly severe due to haze and light reflected from the snow covered ground. Under such conditions, sensory illusions in flight are only part of the problem; a noticeable loss of depth perception increases the hazard. All these illusions are mistakes in interpretation caused by inadequate information on which to establish a reference. Your eyes are reporting correctly to your brain, but there isn't enough information for the brain to interpret. This situation is worse at night than during the day, for your eyes are furnishing less information. Under such conditions your eyes can send false messages to the brain. Have you ever been stopped at a traffic signal and then had another automobile pull along side? Although you were stopped, did you have the illusion your car was backing up slowly only to find that you were indeed stopped and the other car was moving up slowly? This is one simple illustration of sensory illusions. There are numerous others that can and do occur while flying aircraft in both Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) conditions. B. PERCEPTION of the SKELETAL MUSCLES The tension of the various muscles in your body assist you in determining your position within a frame of reference, as well as any motion with respect to this reference. Compared to the eyes and vestibular apparatus, however, these muscles (known as the proprioceptors) play a very small role in determining orientation. However, no matter how small a part the proprioceptors play in determining perceived direction in the air, they can give some indication of position by the pressure of your body in the seat of the aircraft and the sensation that gravity is being applied along a line from the earth passing vertically through the seat. The feeling can occur regardless of the aircraft's reference point to the earth. This means that even though the muscle sense indicates to the pilot that the aircraft is flying a straight and level course, the aircraft may actually be in a coordinated turn. 10-2 C. THE VESTIBULAR APPARATUS The Inner Ear consist of an auditory and non-auditory portions. The latter is primarily associated with equilibrium and contains the three semicircular canals. The semicircular canals are filled with a thick fluid and each canal lies at an approximate 90 degree angle to the other. One end of each canal is enlarged and in this area is a mound of sensory hair cells. Angular acceleration, or rotation, of the body along either the yaw, pitch, or roll axis will move the fluid in a respective canal. This movement displaces the sensory hairs and an impulse is sent to the brain to be interpreted as motion about a known axis. The hairs that project into the fluid are extremely fine, light, and sensitive. Any acceleration greater than 2 degrees per second will cause the hairs to displace and an impulse is sent to the brain that indicates which way the hairs are bent, the brain then figures out the plane of rotation. Since the canals lie in different planes, they can report movement in all three dimensions (yaw, pitch, and roll). This system works fine for sudden, short turns, but, if the turn continues at a constant rate for a period of time, (approximately 25 seconds) the motion of the fluid catches up to the speed of the canal walls, and the hairs are no longer bent. In this scenario, a pilot would initially feel a turn to the right, but, after 25 seconds, as long as the rate of the turn is constant, the pilot would feel as though the turn has stopped, when in actuality, this pilot is still turning to the right. Once the turn to the right is detected, and the turn is stopped, the fluid in the canal will continue to move. In this situation, the hairs that were straight because the fluid and canals were moving at the same rate, would suddenly bend in the opposite direction. This would cause an opposite sensation as though one was now turning hard to the left. An untrained pilot in this situation would, more than likely, turn the aircraft back to the right to compensate for the perceived left turn. As a result, a pilot would try to counteract this imaginary motion by turning back into the original turn or spin. This is the physiology behind the classic Graveyard Spin or Spiral. 10-3 As angular acceleration begins, the canal(s) wall will rotate as the body rotates. The fluid in the canal will lag behind causing the sensory hairs to deviate from their normal erect position (see example A). As the rotation continues at a constant rate for approximately 25 seconds, the fluid will move at the same rate as the canal, the sensory hairs will come back to the erect position, and the sensation of turning will not be felt (see example B). If the rate of the turn decreases or if the turn stops, the fluid, due to inertia, will continue to move and will bend the sensory hairs in the opposite direction (see example C). When the brain perceives angular motion from a canal, it will cause the eyes to react to the motion. In an attempt to keep everything in your visual field during rotation, the eyes will sweep opposite of the plane of rotation. So in the example of the person turning to the right, the eyes would sweep to the left. This system works well during the rotation. The problem is that when the angular acceleration stops, and the fluid in the canals continues to, the eyes continue the sweeping motion for up to 30 seconds of completion of rotation. This condition is called nystagmus. A pilot in this situation could, for example, be turning onto a final approach. After the turn is completed, the pilot, who is trying to scan VASI bars for example, would find that the bars are sweeping side to side, making them very tough to scan. During angular acceleration in one plane of motion, the pair of canals (one in each ear) lying in that plane will be the only ones stimulated. But if one were to deviate one's head position during angular acceleration, another canal would be stimulated. This would send two conflicting impulses to the brain. The brain would have a difficult time trying to process the information coming from the two canals, and would find a "happy medium" to accommodate the signal. This gives a person a very strong illusion called Coriolis. In this scenario a pilot would be turning to a new heading, if the pilot moves the head during this turn by looking down at an approach plate or up at a switch or toggle, this could give the pilot a sensation that the aircraft is making a violent roll or pitch. An untrained pilot may possibly put the aircraft into an unusual attitude. If an aircraft slowly tips to one side while a pilot is distracted, the rate of the roll can be so slow that the pilot may not detect it. This is called Sub-Threshold Acceleration and can be a very dangerous illusion. Any angular acceleration greater than 2 degrees per second will be detected by the semicircular canals. If the rotation is slower than this rate, angular accelaration may go unnoticed. This is the basic physiology behind a common illusion called the leans. A pilot in this situation would, as mentioned above, slowly roll to the right or left. The rotation, if less than 2 degrees per second (sub threshold), would be unnoticed. Once the pilot checks the instrument panel and detects the roll, the pilot would attempt to go straight and level. When the pilot comes about level there will be a strong sensation of rolling to the opposite side. An untrained pilot may put the aircraft back into the initial roll because that "feels normal." FLIGHT FACTORS CONTRIBUTING TO SPATIAL DISORIENTATION 1. Changes in angular acceleration. 10-4 2. Flying in Instrument Flight Rules (IFR) conditions. 3. Low level flight over water. 4. Frequent transfer from Visual Flight Rules (VFR) to IFR conditions. 5. Unperceived changes in aircraft attitude (Sub-Threshold Acceleration) WHAT TO DO TO BEAT SPATIAL DISORIENTATION From all this you can see that, individually treated, each type of illusion can cause a great deal of trouble. Since this is precisely what may happen if you are not careful, let's see what you can do to beat these illusions. First of all, you probably appreciate the fact that sensory illusions or vertigo are problems that usually show up under instrument conditions. Whenever the visibility is poor enough to prevent you from double-checking your equilibrium sense with your eyes, your equilibrium system is undependable. That is why your aircraft provides you with an artificial equilibrium system for indicating bank angle (turn & bank indicator), aircraft attitude (attitude indicator), pitch angle (VSI), and so forth. This system is much more reliable than anything you are equipped with, but it's not easy to use, primarily because you were not born with it. All your life on the ground you have been navigating by your eyes, and you are accustomed to doing what they tell you to do. Now, when you fly by instruments, you are told to ignore your senses and put your faith in dials and indicators. 1. Use Your Head. There are several points to remember about instrument flying. The first is that you can learn to do it, but you have to use your head. Flying by instruments is a skill that can be highly developed. You have to read and interpret the instruments and act accordingly. At the same time, you must have confidence in the instruments and ignore any other signals your body gives you. This procedure usually slows you down a bit. Tests show that flyers interpret the actual horizon about one-fifth of a second faster than they interpret instruments. Furthermore, pilots make a recovery from a dive about one and a half second faster under VFR conditions as opposed to IFR conditions. Pilots are also more susceptible than usual to the stresses of flight such as fatigue, oxygen lack, and anxiety. These stresses may reduce the pilot's ability to think straight, so there is the danger of forgetting to use instruments when things get tough. Anything that produces an emotional upset is likely to disrupt conscious mental processes and make the pilot much more susceptible to illusions or false sensation. 2. Rare Sensations 10-5 10-6 The second point to remember is that the illusions that have been described in this section are relatively rare. Believe it or not, this can actually be a disadvantage. You learn to adjust to the sensations of normal flight as you gain flying experience, but the possibility remains that you will suddenly encounter a vivid illusion you have never experienced before. If you don't know what the illusion is or how you can handle it, you are likely to get panicky and let your emotions take over. When this happens, you are putting your life in the hands of your senses, and under such conditions they may prove to be inadequate. 3. Trust Your Instruments. Last, but not least, remember that many accidents occur as a result of indecision about going on instruments. With poor visibility you may begin to go on instruments too late and then sensory illusions can make you believe your instruments are wrong. There is just one way to beat false interpretation of motion. Put your faith in your instruments and not your senses. Know what kind of tricks your senses can play on you, keep calm, and have confidence in your instrument panel. Once you have acquired this confidence, you can fly at night and in weather as easily as if you were following railroad tracks, two creeks, and a cornfield back to the airport. The moral is simple: The transition from VFR to IFR must be a complete and trusting transition. CONCLUSION Anytime there is low or no visual cue coming from the outside of the aircraft, you are a candidate for spatial disorientation. Developing the dicipline to trust your instruments is achieved through training practice. Trusting what your instruments are telling you and disreguarding what your body is telling you is the key to control disorientation and its dangerous illusions. SELF IMPOSED STRESS In defining self imposed stress it is necessary first to define stress. In the DORLAND'S ILLUSTRATED Medical Dictionary, stress is defined as "the sum of the biological reactions to any adverse stimulus, physical, mental, or emotional, internal or external, that tends to disturb the organism's homeostasis (body's natural balance)". Should these compensating reactions be inadequate or inappropriate, they may lead to disorders. It is difficult to measure the full effect that stress can have, but we are aware of some of the contributing factors that can increase the amount of stress one is experiencing. These contributing factors are known as self-imposed stresses. Among these factors is the use of alcohol, drugs, tobacco, physical fitness, diet, fatigue, and disruption of the circadian rhythm problems. As we determine the effects of each of these stresses, it is also important that we point out how each might affect your job performance, or in this case, your ability to perform your flying duties efficiently. We are all aware of the dangerous side effects that alcohol has on your driving ability. It's not difficult to figure out then that alcohol, in any quantity, can have an adverse effect on your flying capabilities. Before we get too in deeply into the effects of alcohol, it is important to note how it generally affects the human organism. The active ingredient in beverages, such as beer, wine, and liquor is ethyl alcohol. Alcohol itself is considered an anesthetic drug that, when ingested in any quantity, is considered a depressant. As a result, cell metabolism is depressed which is most noticeable in the brain. Since cell metabolism is depressed, so too is the utilization of oxygen being delivered to the cells. What is experienced as a result is histotoxic hypoxia. Below is a list of performance losses caused by alcohol: - Judgment (Normal cautionary attitudes are lost) - Efficiency of eye movement and hearing - Speed and strength of muscular reflexes. - Sense of responsibility - Inhibitions and worries lessens - Relevance of response - Skill reactions and coordination - Ability to see under dim illumination - Insight into existing capabilities - Memory and reasoning ability - Judgment, comprehension, fine attention - Altered perception to situation - Dehydration 11-1 Since every individual is physiologically different, the symptoms experienced from the ingestion of alcohol will vary in severity and intensity. One reason for this variance is the rate of alcohol absorption, which depends on such things as the following: - Type and quantity of food in the stomach - Degree of dehydration - Concentration of alcohol in the beverage - How fast it is consumed - Body weight Another factor is the rate of absorption of the alcohol. On average, our liv