Physiology of Flight Know the physiology of flight.

Physiology of Flight Know the physiology of flight.
1. Describe the physiological divisions of the flight environment. 2. Define the physical laws of gases according to Boyle’s Law, Dalton’s Law, and Henry’s Law. Lesson Objective: Know the physiology of flight. Samples of Behavior/Main Points: 1. State the layers of the atmosphere and the composition of each. 2. Describe the physiological divisions of the flight environment. 3. Define the physical laws of gases according to Boyle’s Law, Dalton’s Law, and Henry’s Law. 4. Describe the processes for respiration and circulation. 5. State the effects of reduced pressure at altitude. 6. Define spatial disorientation and motion sickness. 7. Describe individual stresses imposed upon a pilot during flight.

Physiology of Flight Know the physiology of flight.
3. Describe the processes for respiration and circulation. 4. State the effects of reduced pressure at altitude. 5. Define spatial disorientation and motion sickness. 6. Describe individual stresses imposed upon a pilot during flight.

Overview 1. Respiration and Circulation
2. Effects of Reduced Pressure at Altitude 3. Rapid Decompression 4. Principles and Problems of Vision In this lesson we will discuss: 1. Nature of the Atmosphere 2. Respiration and Circulation 3. Effects of Reduced Pressure at Altitude 4. Rapid Decompression 5. Principles and Problems of Vision

Overview 6. Spatial Disorientation and Motion Sickness
7. Acceleration and Deceleration: Increased G-Forces 8. Noise and Vibration 9. Heat and Cold During Flight 10. Noxious Gases and Vapors 11. Self-Imposed Stresses 6. Spatial Disorientation and Motion Sickness 7. Acceleration and Deceleration: Increased G-Forces 8. Noise and Vibration 9. Heat and Cold During Flight 10. Noxious Gases and Vapors 11. Self-Imposed Stresses

PRE-TEST

VOCABULARY: Physiology = the organic processes or functions in an organism or in any of its parts.

VOCABULARY: Hypoxia = deficiency in the amount of oxygen delivered to the body tissues

Valsalva = a maneuver to clear your ears to equalize pressure
VOCABULARY: Valsalva = a maneuver to clear your ears to equalize pressure

VOCABULARY: M-1 = a maneuver to constrain your vessels and muscles to keep blood from rushing to your feet during G-loads

Physiology of Flight

Nature of the Atmosphere
Composition of the atmosphere 78% nitrogen, 21% oxygen, 1% carbon dioxide. Nitrogen is not used by body to support life. Blood and other body fluids contain nitrogen. Blood carries oxygen to all parts of the body. Oxygen decreases at higher altitudes. Composition of the atmosphere Consists of roughly 78% nitrogen, 21% oxygen, and 1% carbon dioxide and other gases. Nitrogen is not used by the body to support life. It serves only to dilute the oxygen and supply additional pressure. The same amount of nitrogen is exhaled as is inhaled. Blood and other body fluids contain nitrogen. This gas may change from the liquid to the gaseous state when a person ascends to high altitudes. Oxygen must be taken into the lungs and absorbed into the bloodstream where the blood carries it to all parts of the body. At higher altitudes the amount of oxygen decreases and the temperature and pressure of the atmosphere also changes.

REVIEW: Nature of the Atmosphere
Layers of the atmosphere Troposphere Most weather occurs in this region Stratosphere Very little moisture Ionosphere Major characteristic-ionization Exosphere 600 to 1,200 miles above Earth Layers of the atmosphere The Atmosphere is defined as the gaseous envelope surrounding the Earth. One way to look at the atmosphere is to divide it into 4 regions. Between each region is a transition layer (-pause). The depths of the different layers of air vary with the time of day, the season, and the geographical location. Troposphere - Most weather (i.e. winds, storms, rain, snow, hail, and clouds) occurs in this region. The wind in the troposphere usually increases with altitude. The jet streams are found at higher altitudes near the tropopause. Stratosphere - There is very little moisture in the stratosphere. The supply of oxygen and the pressure of the atmosphere are not adequate to sustain life. Most jet aircraft fly in the lower stratosphere to avoid bad weather. Ionosphere - The atmospheric pressure continues to decrease with height. The name of this region suggests its major characteristic, ionization. In this layer, solar radiation causes the molecules of air to break into particles, some with positive charges and some with negative charges. Exosphere - Extends from about 600 to 1,200 miles above the Earth. Atmospheric density continues to decrease with altitude. A region is reached where particle density is so small that it is called "space". There are so few molecules in this region that they seldom strike each other. Only spacecraft can operate in the exosphere and the ionosphere. The greater the height within the exosphere, the thinner the air.

Physiological Divisions of the Atmosphere

DRAW THIS IN YOUR NOTES! Physiological Divisions Physiological zone
Extends from sea level to 10,000 feet Physiological-deficient zone Extends from 10,000 to 50,000 feet Space-equivalent zone Extends from 50,000 feet to 120 miles above Earth Total space-equivalent zone Beyond 120 miles above Earth Physiological Divisions - Pressure variations affect the body in different ways. Consequently, the flight environment is divided into four zones. Pressure within the atmosphere is measured with a barometer. It is expressed in terms of the height of a column of mercury (Hg) which could be supported by a given atmospheric pressure. The pressure of the atmosphere at sea level is 760 mm of Hg. Physiological zone - The region of the atmosphere where man is physiologically adapted to flight. Extends from sea level to 10,000 feet. Within this zone there is enough oxygen to allow a normal, healthy person to fly without using special protective equipment. Most small, unpressurized aircraft fly in this zone. A person may experience some dizziness or discomfort in the ears and sinuses when making a rapid ascent or decent, but the changes in the body do not usually produce physiological impairment. During ascent atmospheric pressure drops from 760 mm Hg to 523 mm Hg. Although it is possible to survive above 10,000 feet without an oxygen mask, the Air Force requires its personnel to use supplemental oxygen when flying above 10,000 feet. Physiological-Deficient Zone - Extends from 10,000 feet to 50,000 feet. Because of the reduced atmospheric pressure, there is inadequate oxygen available to sustain normal physiological functions. The body must be supplied with supplemental oxygen provided under pressure. Atmospheric pressure decreases from 523 mm Hg at 10,000 feet to 87 mm Hg at 50,000 feet. Decompression sickness can occur in body tissue and joints. Most military and commercial aircraft flying long distances fly in this zone with the aid of protective equipment. Space-Equivalent Zone - Extends from 50,000 feet above the Earth. Atmospheric pressure is so low that a man would lose consciousness even if supplied with 100% oxygen. Men flying aircraft within this zone must have a completely sealed cabin. The cabin must have its own internally supplied oxygen and the capability to remove carbon dioxide and to purify the air. Pilots must wear pressure suits for additional protection. Total Space-Equivalent Zone - Beyond 120 miles from the Earth is the total space-equivalent zone. Has all the characteristics of true space as far as the human body is concerned. The concern is with the general problems of flight physiology, especially those that arise from reduced atmospheric pressure at altitude.

Nature of the Atmosphere
Physical Laws of Gases Boyle’s Law The volume of a gas is inversely proportional to its pressure if the temperature remains constant. Dalton’s Law The total pressure of a mixture of gases is equal to the sum of the partial pressure of each gas in that mixture. Henry’s Law The amount of a gas in a solution varies directly with the partial pressure that gas exerts on the solution. Physical Laws of Gases Boyle's Law - States that "the volume of a gas is inversely proportional to its pressure if the temperature remains constant." When the pressure of a gas decreases at constant temperature its volume increases, and vice versa. This law explains why gases trapped in the body expand as the atmospheric pressure on the outside of the body decreases with increasing altitude. Dalton's Law - States that “the total pressure of a mixture of gases is equal to the sum of the partial pressure of each gas in that mixture.” Applied in computing the pressure required for an artificial breathing atmosphere used in aircraft and spacecraft. The pressure of a pure-oxygen atmosphere in a spacesuit can be made about the same as the partial pressure of oxygen at sea level. Henry's Law - States that "the amount of a gas in a solution varies directly with the partial pressure that gas exerts on the solution." When the partial pressure of a gas decreases with altitude, that gas evolves, or comes out of the solution from the blood or other body fluids. Henry's law explains why nitrogen and other gases escape from the solution and form innumerable tiny bubbles in the body as the surrounding pressure decreases. The problems caused by evolving nitrogen are among the most serious problems of flying at high altitudes.

Respiration and Circulation
Respiration is the exchange of oxygen and carbon dioxide between an organism and its environment. Closely related to circulation of blood throughout the body. Respiration can be defined as the exchange of oxygen (O2) and carbon dioxide (CO2) between an organism and its environment. The respiration process is closely related to circulation of blood throughout the body. All processes and systems of the body are affected in some way by the stresses of flight. But respiratory and circulatory systems are most directly affected.

Decreasing oxygen pressure places stress on the body affecting the respiratory system first. Made up of the lungs, bronchi and their small branches, windpipe, mouth, and the nose. Air enters the nasal passages where it is warmed and moistened and foreign matter removed. Decreasing oxygen pressure places stress on the body affecting the respiratory system first. The respiratory system is made up of the lungs, bronchi and their small branches, windpipe, mouth, and the nose. Air first enters the nasal passages where it is warmed and moistened and small particles of foreign matter removed. The air then passes down the throat, through the windpipe, into the bronchial tubes, and then into the lungs.

Once inside the lungs, the air goes through many thousands of small tubes that branch off from the large tube. Located at the very end of each branch are air sacs, known as the alveoli. Surrounding the thin, moist wall of each alveolus are tiny blood vessels, or capillaries. Because the walls of the alveoli and the capillaries are very thin, gases in solution can readily pass back and forth into and out of the blood that flows through the capillaries. Oxygen passes from the alveoli into the bloodstream because the partial pressure of oxygen in the alveoli is greater than that in the bloodstream. Air, like water, seeks its level, passing from an area of higher pressure into one of lower pressure. Once the supply of oxygen enters the bloodstream from the lungs, it is circulated by the action of the heart. The arteries carry the oxygen-rich blood away from the heart to the body tissues. The veins carry the deoxygenated blood back from the tissues to the heart.

The amount of carbon dioxide in the blood has an important effect on the action of the heart. As carbon dioxide in the blood increases, the heart rate speeds up so the heart can send more oxygenated blood to the tissues. When carbon dioxide in the blood decreases, the heart rate slows because tissues need less oxygen. The amount of carbon dioxide in the blood has an important effect on the action of the heart. As concentrations of carbon dioxide in the blood increases, it causes the heart rate to speed up so that the heart can send more oxygenated blood to the tissues. When the amount of carbon dioxide in the blood decreases, the heart rate is slowed because the tissues need less oxygen.

The respiratory system acts to keep the amount of oxygen in the body tissues constant. The respiratory system acts to keep the amount of oxygen in the body tissues constant. To make up for reduced oxygen pressure at altitude, the human body begins to inhale more rapidly. Inhalation occurs when air in the lungs reaches the same pressure as the ambient air, the muscles relax and the diaphragm moves upward, causing the thorax to contract. With decreased volume, the pressure of the gases in the thorax and lungs increases, forcing the air out of the lungs. Exhalation has occurred.

Effects of Reduced Pressure at Altitude
As the body goes to high altitude it must make adjustments to the reduced atmospheric pressure in order to keep the body tissue constant. If the pressure outside the body is greatly reduced and the body is not adequately protected, it cannot make the necessary adjustments. As the body goes to high altitudes, it must make adjustments to the reduced atmospheric pressure in order to keep the body tissue constant. If the pressure outside the body is greatly reduced and the body is not adequately protected, it cannot make the necessary adjustments.

Hypoxia - a deficiency of oxygen in the body cells or tissue. Most frequently the result of decreased pressure on an unprotected body. In flight is usually caused by an insufficient amount of oxygen in the inhaled air. Greatest danger when pilot becomes engrossed in duties and doesn’t notice the first symptoms. Hypoxia can be defined as a deficiency of oxygen in the body cells or tissues. It is the most frequent result of decreased pressure on an unprotected body. In flight it is usually caused by an insufficient amount of oxygen in the inhaled air . It may be aggravated by other conditions, such as anemia, poor circulation of the blood, or the presence of poison or alcohol in the body. The greatest danger of hypoxia in flight occurs when the pilot or aircrew member becomes too engrossed in duties to notice the first symptoms of hypoxia. At first the symptoms may include an increased breathing rate, dimming of vision, headache, dizziness, poor coordination and impairment of judgment, loss of vision and changes in behavior (euphoria or belligerence). Whenever a pilot notices the first symptoms of hypoxia, he must use additional oxygen or if oxygen is not available, make an emergency descent to a lower altitude.

Hyperventilation A person affected by hypoxia tends to increase breathing rate in an attempt to take in more oxygen. May result from great emotional tension or anxiety. Hyperventilation A person affected by hypoxia tends to increase his breathing rate in an attempt to take in more oxygen. He continues to gasp until hyperventilation, or overbreathing occurs. Hyperventilation may also result from great emotional tension or anxiety, such as a pilot is likely to experience under the stresses of high altitude. As aviators gasp for air, they "blow off" an excessive amount of carbon dioxide from the lungs and "wash out" carbon dioxide from the bloodstream. A certain level of carbon dioxide must be kept in the bloodstream at all times to signal the respiratory center in the brain to bring in more oxygen. When the blood has too little carbon dioxide, the respiratory center in the brain ceases to function properly. Insufficient oxygen is then brought into the blood. The aviator usually has symptoms similar to those of hypoxia. These include dizziness, hot and cold sensations, nausea, muscle tightness and twitching, paleness, cold clammy skin, and finally unconsciousness.

Trapped Gases-Ear Block Trapped Gases - Ear Block The middle ear is part of the ear that trapped gases will most likely affect during flight. Problems occur more often at altitudes closer to the Earth's surface where there are greater pressure changes. The middle ear connects with the back wall of the throat and outside air through a short slit-like tube called the eustachian tube. As a person ascends or descends during flight, air must escape or be replenished through the eustachian tube. Otherwise, the pressure in the cavity of the middle ear will be different than the outside atmosphere. This adjustment is usually made automatically during ascent, but has to be made consciously during descent. The eustachian tube allows air to pass outward with ease but resists passage of air in the opposite direction. Air can usually be pushed through the eustachian tube during decent by swallowing, yawning, or tensing the muscles of the throat at intervals. This causes the pressure of the air within the middle ear to equalize with the outside atmosphere. An ear block is characterized by congestion, inflammation, discomfort, pain, and is usually followed by a temporary impairment of hearing. Inflammation or infection from a head cold, allergy, sore throat, infection of the middle ear, sinusitis or tonsillitis will restrict the eustachian tube opening. The most effective way to equalize the pressure in the middle ear is the use of the Valsalva maneuver. Force air into the middle ear by closing the mouth, pinch the nosed closed and forcefully exhale. This force pushes air through the previously closed eustachian tube and equalizes the pressure differential between the middle ear and the atmosphere.

Trapped Gases-Sinus Block Trapped Gases - Sinus Block At high altitudes the sinuses may also become blocked. The sinuses are rigid bony cavities filled with air and lined with mucous membrane. There are four sets of sinuses. Each sinus connects with the nasal cavity by means of one or more small openings. Under normal conditions, the air can pass freely in and out of the sinus cavities equalizing pressure. If an ascent or descent is made too rapidly or if the openings to the sinuses are blocked because the mucous membrane is swollen, pressure builds up within the sinuses. The frontal sinuses are the ones most often blocked. Pressure in them causes a pain above the eyes that may become severe. When maxillary sinuses are affected, a pain develops in the upper jaw. The Valsalva maneuver will usually alleviate the problem. If necessary, relief from pain can be obtained by ascending to an altitude where pressure equalization can be accomplished.

Trapped Gases-Tooth Pain Untreated cavities where pulp is exposed may be the cause of tooth pain at altitude. The toothache often disappears at the same altitude that if was first observed on ascent. Gases may be trapped in the teeth at altitude in abscesses. Trapped gases - Tooth Pain Untreated cavities, especially those under restorations and where pulp has become exposed, may be the cause of tooth pain at altitude. The toothache often disappears at the same altitude that it was first observed on ascent. Gases may be trapped in the teeth at altitude in abscesses, imperfect fillings and inadequate root canals. Good dental hygiene is the most practical way to prevent tooth problems at altitude.

Trapped Gases-Stomach and Intestines In flights above 25,000 feet the expanding gases may cause severe pain, lowering blood pressure and eventually shock. Usually air that has been swallowed. When barometric pressure falls the partial pressures of the gases in the body fluids decrease. The escaping gases cause decompression sickness. Gases Trapped in Stomach and Intestines In flights above 25,000 feet the expanding gases in the stomach and intestines may cause severe pain, lowering blood pressure and eventually bringing on shock. The gas trapped in the stomach and intestines is usually air that has been swallowed. But other gas, or flatus, may develop in the digestive process. Crewmembers who fly to high altitudes and astronauts are careful about the foods they select for their preflight meal. During flight, they do not eat foods that form gas in the stomach and intestines. Other gases that cause problems in flight are those that have evolved or changed from a liquid back to a gas. When the barometric pressure falls during ascent, the partial pressures of the gases in the body fluids decrease. The decreases are in proportion to the amount of each gas in the fluid, according to Henry's law. The gases that are in the highest degree of concentration begin to leave the body fluids. They escape in the form of tiny bubbles. These escaping gases cause a number of disturbances known collectively as decompression sickness. Nitrogen is the gas found in the greatest proportion in the body. It is the first gas to come out of solution in the body as pressure decreases. It is, therefore, the first gas to come out of solution in the body as pressure decreases. Evolved nitrogen causes the bends, the chokes, and other forms of decompression sickness.

The Bends Release of nitrogen into the joints of the body. The Bends develop from the release of nitrogen into the joints of the body, causing pain. The pain is generally localized in and around the joints of the body. The smaller joints can be involved; however, the larger joints like the shoulders, elbows, knees, and ankles are usual sites. The pain is variable in nature and may occur suddenly. It is usually a deep and dull pain. Factors such as exercise, time at altitude, and increased altitude may influence the degree of pain. Descent below the altitude of occurrence will usually decrease or resolve the pain.

The Chokes Another form of decompression sickness. Deep, sharp pains under the sternum. Increased expansion of the lungs causes the pain to increase. Chokes are another form of decompression sickness. They are rare, but potentially very dangerous because of the existence of bubbles in the smaller blood vessels in the lungs and in the tissue of the trachea (windpipe). The symptoms are deep, sharp pains under the sternum, a dry progressive cough, and difficulty with inspiration. Increased expansion of the lungs causes the pain to increase and there is a sense of suffocation and apprehension.

Skin Symptoms Type of decompression sickness that involves sensations of the skin. Small bubbles of nitrogen under the skin produce itching, hot and cold feelings and tingling. The rash does not disappear with descent and may last for hours. Skin symptoms are a type of decompression sickness that involves sensations of the skin that may be accompanied by a rash. Very small bubbles of nitrogen under the skin producing itching, hot and cold feelings, and tingling cause this rash. The rash may be localized in a small area or may be diffused over the body. The rash does not disappear with descent and may last for hours. Skin symptoms warn that continued exposure may result in more serious decompression sickness.

Treatment of Decompression Sickness As decompression sickness becomes more severe, the pain caused by escaping gas bubbles becomes more intense. As symptoms appear in flight, 100% oxygen should be administered. If symptoms still exist after landing, compression therapy will be administered at the nearest hyperbaric facility. Treatment of decompression sickness As decompression sickness becomes more severe, the pain caused by the escaping gas bubbles becomes more intense. Faintness, dizziness, and nausea may result. The victim will go into shock and become unconscious. Anytime an occupant of an Air Force aircraft appears to be experiencing the symptoms of decompression sickness, 100% oxygen should be administered and the affected area immobilized. The aircraft should land at the nearest suitable installation where medical assistance can be obtained. If symptoms still exist after landing, compression therapy will be administered at the nearest hyperbaric facility. Compression therapy results in reduction of the size of the nitrogen bubbles and resolves decompression sickness.

Rapid Decompression Rapid decompression at a high altitude brings on an explosion as the pressure suddenly decreases. At 63,000 feet or above body fluids boil if exposed to the ambient atmosphere. The time of useful consciousness may be reduced by 60% if the decompression is rapid and the air is forced out of the lungs due to rapid expansion. Occasionally an aircraft cabin loses pressure (decompresses) during flight. If decompression should occur, the aircraft occupants are immediately exposed to the inherent hazards of high altitude. Rapid decompression at a high altitude brings on an explosion as the pressure suddenly decreases. This exposes the occupants of the cabin to extremely low temperatures, flying debris, and possibly windblast. In an aircraft or spacecraft flying at 63,000 feet or above, there is an additional hazard. The blood and other body fluids boil if exposed to the ambient atmosphere at this level. At sea level water boils at 212o F. As more heat is applied to the water, bubbles and steam form, and the temperature of the boiling water remains at 212o F. At higher altitudes, the barometric pressure falls. This decreases the boiling point and evaporation takes place at a lower temperature. The body contains blood and other fluids that are largely water. The body keeps these fluids at a temperature of about 98.6o F. Since the boiling point of water decreases with altitude, a point is finally reached at which the boiling point of water (and body fluids) becomes 98.6o F. (63,000 ft.) Only military aircrew members and astronauts fly at such high altitudes. If a space cabin undergoes rapid decompression at levels below 63,000 ft, the chief danger is from hypoxia, or lack of oxygen. A normal healthy person can survive relatively severe decompression without harm to the body if the air passages in the lungs remain open. The time of useful consciousness may be reduced by 50 to 60 percent if the decompression is rapid and the air is forced out of the lungs due to rapid expansion.

Principles and Problems of Vision
Structure and Physiology of the Eye - The cornea and lens refract (bend) light and focus it on the retina in a manner similar to the lens of a camera. Photoreceptors in the retina are stimulated and messages are sent to the brain, via the optic nerve, where the process of perception takes place. The retina is the innermost layer of tissue in the eye, containing millions of photoreceptors (rods and cones) allowing an image to be seen. The rods and cones are distributed over the entire retina, except where the optic nerve and blood vessels exit the eyeball. This site is the optic disk or blind spot. The optic disks are located in different locations in each eye. Since there are no photoreceptors at this site, it is effectively an anatomical blind spot. Therefore, when the eyes are being used simultaneously, the nerve impulses from the retina provide the brain with an image negating the effects of the blind spot. The blind spot will only be noticed when an object is being viewed with one eye. This situation can occur when a canopy rail, oxygen mask, or even your nose obstructs one eye. When this blind spot occurs, the brain "fills in" the "missing" visual information with "surrounding" visual information. This process is hazardous if you are scanning for other objects and there is an obstruction in your field of view exposing one of the blind spots. If you look at an object and it's focused on your blind spot, you will not "see" the object. If the object happens to be another aircraft, you won't see the aircraft until the image grows large enough on the retina to fall on the photoreceptors surrounding the optic disk. The fovea is next to each optic nerve. It is a tiny pit containing only cones and the natural point on the retina where the lens focuses an image. Our best color vision and maximum visual acuity are in the fovea. The fovea of each eye is offset to help a person have stereoscopic depth perception to roughly 200 meters.

Spatial Disorientation and Motion Sickness
Spatial disorientation - the inability to accurately orient yourself with respect to the Earth’s horizon. We use four sensory systems to maintain our orientation and equilibrium (balance). Spatial disorientation is defined as the inability to accurately orient oneself with respect to the Earth's horizon. Four sensory systems are used to maintain orientation and equilibrium (balance). Information from each sensory system is sent to the brain, which coordinates all the input. If the input from each system agrees with the others, the individual is "oriented". If there is a mismatch between systems the individual becomes disoriented, motion sick or both will occur.

The Visual System Eyes provide the strongest and most reliable orientation information during flight. When the horizon is not correct, your vestibular disorientation disappears; you may still experience visual illusions caused by false horizon. The Visual System The eyes provide the strongest and the most reliable orientation information during flight. If you become disoriented flying in clouds (because of confusing vestibular input), and then fly out of the clouds and acquire an accurate horizon, the disorientation disappears almost instantly. When the horizon is not correct, your vestibular disorientation disappears. You may still experience visual illusions caused by the false horizon. Use your focal vision by concentrating on the flight instruments to ensure the aircraft flies correctly.

The Vestibular System The Vestibular System The vestibular system is located in the inner ear and consists of two subsystems, the semicircular canals and the otolith organs. The semicircular canals- there are three canals in each ear, oriented at right angles to one another in the pitch (vertical), roll (lateral), and yaw (horizontal) axes. They measure angular acceleration caused when the head is turned or tilted. Each semicircular canal contains a fluid called endolymph that is stimulated into motion when the head accelerates in the axis of the canal. When the head is accelerated, the fluid in the canal lags behind because of inertia. This motion causes a concentration of specialized nerve cells called the cupula to bend in the direction of the fluid motion. The bending of the cupula sends a signal to the brain that interprets the signal as changes, position, or attitude.

The Vestibular System The Vestibular System The otolith organs are located near the base of the semicurcular canals and sense linear acceleration. They consist of a base of nerve cells with hair like appendages that are embedded in a gelatinous substance containing calcium carbonate crystals. As you tilt your head forward or back, the crystals slide in that direction and the nerves signal the brain that the head is tilted in that direction. If you accelerate forward, the crystals slide to the rear and, in the absence of a visual horizon, you sense the aircraft is pitching up.

The Somatosensory System Consists of tactile pressure receptors in the skin, muscles, tendons and joints. Often called the “seat-of-the-pants” sense. The Somatosensory system consists of tactile pressure receptors in the skin, muscles, tendons and joints. The pressure receptors are used to help maintain posture and balance. The somotosensory system is often called the "seat-of-the-pants" sense. In-flight, the somotosensory system is useless as an orientation system in the absence of correct visual cues. Because most flight maneuvers are made in the positive-G environment, there are no variations in pressure cues. Therefore, the somotosensory system does not receive adequate input to tell the somotosensory receptor if the aircraft is in a bank, nose up, nose down or inverted attitude.

Acceleration and Deceleration: Increased G-Forces
When military flight crews perform maneuvers or when astronauts are launched or recovered they may be subjected to severe stress from the effects of acceleration and deceleration. The stresses are felt as increases in weight or gravity forces (G-Forces). The effects of acceleration and deceleration during commercial flights may cause some passengers to experience disorientation and motion sickness. But these effects are not prolonged and are not severe enough to be classed as flight stress. When military flight crews perform maneuvers or when astronauts are launched or recovered, they may be subjected to severe stress from the effects of acceleration and deceleration. When the body is subjected to large amounts of acceleration or deceleration during flight, the stresses are felt as increases in weight or gravity force or G-forces.

Acceleration and Deceleration: Increased G-Forces
The direction of force determines the type of G-force you experience. They are transverse G, negative F, and positive G. Transverse G force is the force applied to the front or back of the body. These forces are normally experienced during takeoffs, acceleration in level flight, and landing. Negative G force is the force being applied from the feet towards the head. Negative G force is not tolerated well by humans and is seldom experienced in high levels during normal flight. Normally negative G force is experienced when the nose of the aircraft is lowered during a "pushover" or when experiencing turbulence. The physical symptoms are a sense of weightlessness, congestion in the head and face, headache, visual blurring and if sustained long enough, a visual anomaly called red-out when the person experiences a reddening of vision. Positive G force is a force applied from the head towards the feet. It occurs during turns and dive recoveries and is the G force most often experienced by crewmembers. Under a positive 4 G-force, a seated crewmember who weighs 150 pounds on the ground would weigh 600 pounds. A person of this weight would be pulled down into the seat. Their arms and legs would feel like lead, their cheeks would sag, and they would be incapable of free movement.

Noise and Vibration Cause flyers more inconvenience than any other factor in flight. Sound intensity or loudness is measured in decibels. Vibrations are measured in frequency. One effect of vibration is blurred vision. Noise and Vibration Noise and vibration probably cause flyers more inconvenience and annoyance than any other factor in flight. Both have an important part in producing headaches, visual and auditory fatigue, airsickness, and the general discomfort experienced at the end of a long flight. Sound intensity or loudness is expressed in decibels (dB). The decibel scale is a relative one that expresses how much greater one sound's intensity is than another. The ear senses sound not only by its intensity, but also by audiowave frequency. The safe level of noise for a crewmember or astronaut varies with the individual. The frequency of the noise, as well as its intensity, must be taken into consideration. The longer the time a person is exposed to a noise and the more intense it is, the greater the danger of damage to the ear. Vibrations are measured in frequency. Vibrations are side-to-side and up-and-down motions. The usual source of vibration in aircraft and spacecraft is the power plant. One effect of vibration in aircraft is blurred vision. At subsonic speeds the principle effect of vibration is to cause fatigue and irritability. Another possible effect is the crewmember may become hypnotized as a result of rhythmic monotonous vibration.

Heat and Cold During Flight
The largest amount of heat is generated on the skin of aircraft and spacecraft as it travels at high speeds through the atmosphere. An aircraft flying at Mach 2 has skin temperatures increased by about 400o F as a result of aerodynamic heating. There are two dangers associated with exposure of the body to cold. High-performance aircraft and spacecraft must dissipate heat to keep the cabin comfortable. Within a closed cabin, heat builds up as it is given off by the human body and the power systems. The largest amount of heat, however, is generated on the skin of the aircraft and spacecraft as it travels at high speeds through the atmosphere. An aircraft flying at Mach 2 (twice the speed of sound) has skin temperatures increased by about 400oF as a result of aerodynamic heating. The Apollo module, as it reentered the atmosphere upon return from the moon, reached 5,000oF. To keep astronauts comfortable within an enclosed cabin or cockpit systems have been designed to keep temperatures at 70 to 75oF and to control humidity. The human body maintains an internal temperature of about 98.6oF and a skin temperature of about 92oF. Aircrew members regulate the temperature of the body by the kind of flight clothes they wear. If the environmental control system and the clothing do not keep the body at comfortable temperatures, the body makes adjustments. The body does this through processes of shivering, perspiring, and enlarging the blood vessels to bring more blood close to the surface of the skin. There are two dangers associated with exposure of the body to cold. The most immediate danger is frostbite on hands, feet, face, and ears. Frostbite is the actual freezing of fluids in the body tissue. The second danger is that the continued exposure to low temperature will reduce efficiency to the point where safe operation of the aircraft or spacecraft is impossible. The temperature at which the cold seriously interferes with human efficiency depends upon air circulation, length of exposure time, clothing, and general physical condition. At temperatures over 85oF, discomfort, irritability, and loss of efficiency are pronounced. High temperatures also reduce ability to cope with other stresses, such as increased G-forces and hypoxia.

Noxious Gases and Vapors
Inside an enclosed cabin, noxious gases and vapors may accumulate. The breathing atmosphere can easily become contaminated from inside sources if care is not taken. Carbon Monoxide. In aircraft cabins that are not completely closed the problems of noxious gases and vapors are not serious. Inside an enclosed cabin, noxious gases and vapors may accumulate. In aircraft that fly above 50,000 feet and in spacecraft, the cabin is completely closed. In this kind of cabin the "atmosphere" must be recirculated and reused over and over again. Maintaining a pure breathing atmosphere is especially important in spacecraft, as the astronauts remain in them for extended periods. In spacecraft there is an environmental control system for cleaning and deodorizing the environment and removing toxic materials. The breathing atmosphere can easily become contaminated from inside sources if care is not taken. Harmful gases and vapors may come in from such sources as the byproducts of human respiration and body wastes. Other sources are exhaust gases, fire extinguishers, fuels, hydraulic fluid, and anti-icing fluid. Carbon monoxide is a lethal gas that is colorless, and tasteless. When carbon monoxide is inhaled, it passes into the lungs through the alveolar wall into the bloodstream. If the air within an enclosed cabin is not purified, carbon dioxide soon accumulates from human breathing. Concentrations of carbon dioxide can impair vision and hearing, as well as affect respiration. High concentrations could result in loss of consciousness and death.

Self-Imposed Stresses
Alcohol One drink at 10,000 feet can have the same effect as two or three drinks at sea level. Tobacco Smoking at 10,000 feet produces effects equivalent to those experienced at 14,000 feet without smoking. Drugs Aspirin, nasal decongestants, tranquilizers or sedatives. Aircrew members must not neglect self-imposed stress because of the effects on their flying proficiency. Self-imposed stresses include excessive or unwise use of drugs, alcohol, or tobacco. Practices that cause no apparent harm to the body on the ground may place stresses on the body at altitude because they interfere with the intake of oxygen. Alcohol - The effect of an alcoholic drink is magnified at altitude. Even at relatively low levels of 10,000 to 12,000 feet, crewmembers' performance would suffer from taking only one drink. One drink at 10,000 feet can have the same effect as two or three drinks at sea level. Clear minds and judgement are necessary to make important decisions instantly. Tobacco - Cigarettes contain harmful nicotine, and carbon monoxide makes up 2.5 percent of the volume of cigarette smoke, and more of cigar smoke. This will reduce ability to see clearly and to adapt your eyes to the dark at sea level to the same extent as in a person experiencing mild hypoxia at 8,000 feet. Smoking at 10,000 feet produces effects equivalent to those experienced at 14,000 feet without smoking. The carbon monoxide in the blood causes a drop in the amount of oxygen that leads to hypoxia. Drugs - Aspirin is probably the most frequently used drug sold over the counter. It causes no toxic effects when used in moderation on the ground. If used excessively at altitude, however, it can interfere with absorption of oxygen by the blood and cause problems. Nasal decongestants, if used excessively, can cause self-imposed stresses at altitude. Tranquilizers or sedatives should not be used by crewmembers before flight. They cause dizziness and dulling of judgement at altitude.

Summary 1. Nature of the Atmosphere 2. Respiration and Circulation
3. Effects of Reduced Pressure at Altitude 4. Rapid Decompression 5. Principles and Problems of Vision 6. Spatial Disorientation and Motion Sickness In this lesson we discussed: 1. Nature of the Atmosphere 2. Respiration and Circulation 3. Effects of Reduced Pressure at Altitude 4. Rapid Decompression 5. Principles and Problems of Vision 6. Spatial Disorientation and Motion Sickness

Summary 7. Acceleration and Deceleration: Increased G-Forces
8. Noise and Vibration 9. Heat and Cold During Flight 10. Noxious Gases and Vapors 11. Self-Imposed Stresses 7. Acceleration and Deceleration: Increased G-Forces 8. Noise and Vibration 9. Heat and Cold During Flight 10. Noxious Gases and Vapors 11. Self-Imposed Stresses

Physiology of Flight Know the physiology of flight.

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Physiology of Flight Know the physiology of flight.

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