United States Army School of Aviation Medicine
Fort Rucker, Alabama
JANUARY 1997
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STUDENT HANDOUT
TITLE: ALTITUDE PHYSIOLOGY
FILE NUMBER: 2/5/9/9E/AA/AC/AD/AE/32-4502-3
PROPONENT FOR THIS STUDENT HANDOUT IS:
United States Army School of Aviation Medicine
ATTN: MCCS-HAF
Fort Rucker, Alabama 36362-5000
FOREIGN DISCLOSURE RESTRICTIONS: The materials contained in this lesson plan have been
reviewed by the instructor/training developer and determined to be public domain
materials. This product is releasable to military students from all requesting foreign
countries without restrictions.
January 1997
ALTITUDE PHYSIOLOGY
TERMINAL LEARNING OBJECTIVE (TLO):
At the completion of this lesson the student will:
ACTION: Manage the physiological effects of altitude.
CONDITION: While serving as an air crew member.
STANDARD: In accordance with AR 95-1, AR 40-8, FM 1-301 and FM 8-2.
SAFETY REQUIREMENTS: Safety requirements will be addressed as NOTES:, CAUTIONS: and WARNINGS:.
RISK ASSESSMENT LEVEL: Low.
ENVIRONMENTAL CONSIDERATIONS: None.
A. ENABLING LEARNING OBJECTIVE (ELO) # 1:
ACTION: Select the physiological zone lethal to humans.
CONDITION: Given a list of the physiological zones of the atmosphere.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Atmosphere
NOTE: The biosphere is that area of our world where life can exist. It includes the atmosphere (air), hydrosphere (water) and lithosphere (earth). All of the atmosphere is not within the biosphere.
(1) Definition - a mixture of gases that surrounds the earth's surface. Consists of a mixture of water vapor and gases that extends from the surface to approximately 1,200 miles. Held in place by gravity, it exhibits few physical characteristics that can be readily observed. Additionally, it shields earth's inhabitants from ultraviolet radiation.
(2) Layers of the atmosphere.
a) Troposphere
1. Lies closest to the earth's surface.
2. Extends to an altitude of about 30,000 feet at the poles and 60,000 feet at the equator. Difference is due to the rising heated air at the equator.
3. Domain of weather - winds, turbulence and convection. Temperature lapse rate is 2° C/1000 feet.
4. Most Army flights take place in this layer.
(b) Tropopause
1. Boundary between troposphere and stratosphere.
2. It has a stable temperature and varies in width.
3. Domain of high winds and highest cirrus clouds.
4. Gradually increases in altitude from the polar regions to the equator.
(c) Stratosphere.
1. Extends upward from the Tropopause to about 50 miles from the earth's surface.
2. Characterized by constant (-55°C) temperature, absence of water vapor and turbulence, cloudless, and has jet streams.
3. Ozone layer at the top.
(d) Ionosphere.
NOTE: The space shuttle orbits at 160 miles above the earth.
1. Extends from the stratosphere to about 600 miles above the earth's surface.
2. Forms a shield around the earth and protects individuals from ultraviolet radiation.
3. Large electron density affects communications.
4. Temperature increases to 1500° C.
(e) Exosphere.
1. Extends from the ionosphere to about 1,200 miles above the earth's surface.
2. Hypothetically true space.
c. Physiological zones of the atmosphere. Man cannot physiologically adapt to all the physical changes of temperature and pressure which occur within the various regions. For this reason, the atmosphere is further divided into three physiological divisions. The primary basis for these physiological zones is the pressure changes which take place in the human body.
(1) Efficient zone.
(a) Extends from sea level to 10,000 feet.
(b) Most individuals are physiologically adapted to this zone.
(c) Oxygen levels within this zone are sufficient for a normal, healthy person without the aid of protective equipment.
(d) Barometric pressure drops from 760mm/hg to 523mm/hg in this zone.
(2) Deficient zone.
(a) Extends from 10,000 feet to 50,000 feet.
(b) Noticeable physiological problems, such as hypoxic hypoxia and evolved gas disorders, occur unless supplemental oxygen is used.
(c) Barometric pressure drops from 523mm/hg at 10,000 feet to 87mm/hg at 50,000 feet.
(3) Space equivalent zone.
(a) Extends upward from 50,000 feet.
(b) Human system is essentially in space. Without an artificial atmospheric environment, this zone is lethal to humans and death will occur rapidly.
d. Composition of the atmosphere. Atmosphere is a mixture of several gases.
(1) Nitrogen (N2): 78%. Most plentiful in the atmosphere. Essential building block of life but not readily used by the body (inert gas).
(2) Oxygen (O2). 21%.
(3) Other gases: 1%. Carbon dioxide (CO2)--contained in the other 1% of gases and is essential to human life. (.03% of that 1% is CO2.)
B. ENABLING LEARNING OBJECTIVE (ELO) # 2:
ACTION: Select the altitude in which total atmospheric pressure is reduced by ½ the pressure found at sea level.
CONDITION: Given a list.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Atmospheric (barometric) pressure - Definition - the pressure due to the weight exerted by the earth's atmosphere.
b. It is an observable characteristic that can be expressed in PSI, mm/Hg, inches of Hg, or in feet as indicated by an altimeter.
c. Percentage composition of atmosphere remains constant but pressure decreases with altitude. This decrease in pressure is responsible for most physiological problems in flight.
d. Standard sea level atmospheric pressure is 760mm/Hg. At 18,000 feet
this atmospheric pressure is reduced to 380mm/Hg or one-half the pressure found at sea
level. The chart shows other significant altitudes and atmospheric pressure reductions.
| ALTITUDE | PRESSURE | |
| FEET | mm/Hg | ATMOSPHERES |
| 18,000 34,000 48,000 63,000 |
380 190 95 47 |
½ ¼ 1/8 1/16 |
e. Dalton's Law of partial pressure.
(1) Definition - the pressure exerted by a mixture of gases is equal to the sum of the partial pressures of each gas in the mixture.
(2) Significance.
(a) The total atmospheric pressure exerted on the body decreases with altitude.
(b) The amount of O2 in a given volume of air decreases with altitude.
(c) The partial pressure of oxygen decreases with increased altitude.
NOTE: While the law states that atmospheric pressure is the sum of pressures of the gases in it, it also means that if the total pressure is decreased, the pressure of each gas must also decrease.
C. ENABLING LEARNING OBJECTIVE (ELO) # 3:
ACTION: Select the component of blood responsible for transporting the majority of oxygen throughout the human system.
CONDITION: Given a list.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Circulation.
(1) Circulatory system - consists of all structures that transport blood throughout the body.
b. Functions.
(1) Oxygen and nutrient (fuel) transport to cells.
(2) Transport of metabolic waste products to organ removal sites.
(3) Assists in temperature regulation.
c. Components of circulatory system.
(1) Arteries - vessels that move blood from the heart to the body tissue.
(2) Veins - vessels that return blood to the heart.
(3) Capillaries.
(a) Connect arteries to veins.
(b) Contact most tissues of the body transferring O2, CO2, nutrients, and waste products between the cells and blood.
d. Components and functions of blood - Makes up approximately 5% of total body weight and is composed of some 45% cells and 55% plasma.
(1) Plasma: 55% of whole blood.
(a) Fluid part of the blood composed mainly of salt, water, and proteins.
(b) One of its important functions is to transport CO2 in the blood.
(2) White blood cells (WBCs).
(a) Differ from RBCs in that they contain no hemoglobin.
(b) Main function is to fight infection or inflammation.
(3) Platelets (Thrombocytes)--small irregular-shaped bodies produced by bone marrow that aid in coagulating the blood.
(4) Red blood cells (RBCs).
(a) Has an iron-containing compound, hemoglobin, which is responsible for the O2 uptake of these cells.
(b) Transport approximately 98.5% of all O2 in the body; the rest is transported in solution within the plasma.
(c) Bright red color of arterial blood results from the combination of O2 with hemoglobin; darker color of venous blood reflects a hemoglobin that has no O2 attached to it.
(d) Produced in the bone marrow and the number RBCs that an individual has depends largely on their environment.
(e) Persons living above 10,000 feet can have as many as 30% more RBCs than an individual living at sea level.
D. ENABLING LEARNING OBJECTIVE (ELO) # 4:
ACTION: Select the active phase of external respiration.
CONDITION: Given a list.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Respiration - Definition - process by which a living organism exchanges gases with its environment.
b. Functions.
(1) Provide oxygen to the cells of the human body.
(2) Remove carbon dioxide from the cells of the human body.
(3) Assists in maintaining body heat balance.
(4) Assists in maintaining body chemical balance.
c. Processes of respiration.
(1) External respiration - lungs are ventilated during inhalation and exhalation and gases are transferred through the lungs in the bloodstream.
(2) Internal respiration - gases are transported to and from body tissues by the blood. Chemical changes take place within the tissue cells to metabolize the oxygen.
d. Phases of external respiration - the respiratory cycle is an involuntary process that continues unless a conscious effort is made to control it.
(1) Active phase - inhalation.
(2) Passive phase - exhalation.
NOTE: Pressure breathing causes a reversal of the active and passive phases of respiration.
e. Control of respiration.
(1) Controlled by the respiratory centers in the pons and medulla oblongata (lower brain).
(2) The uptake of O2 and CO2 takes place through extensive chemical changes in the hemoglobin and plasma of the blood.
(3) If the chemical pathways are disrupted, the chemical balance of the body changes.
(4) Normal pH level in the body is approximately 7.4 (slightly alkaline).
(5) During respiration, the CO2 elevates, the acidity level increases, and the pH value lowers to less than 7.4
(6) Conversely, too little CO2 causes the blood to become more alkaline and the pH value to rise.
(7) Since the human body maintains equilibrium within narrow limits, any shift in the blood pH and CO2 levels is sensed by the respiratory center of the brain.
(8) When unusual levels occur, chemical receptors trigger the respiratory process to help return the CO2 and pH level to normal limits.
f. Components of respiratory system.
(1) Oral-nasal cavity. The nose is an efficient filter which removes small particles from the air.
(2) Pharynx.
(a) Back of the throat and is connected to oral and nasal cavities and the trachea.
(b) Primarily humidifies and warms the air entering the respiratory system.
(3) Trachea ("Windpipe").
(a) Tube through which air moves down into the bronchi.
(b) From here, air continues to move down through the bronchi and increasingly smaller passages, or ducts, until it reaches the alveoli.
(c) Additional responsibility of expectorating or swallowing mucus moved there by cilia.
(4) Alveoli.
(a) Small sacs surrounded by a network of capillaries.
NOTE: There are about 300 million alveoli in a pair of human lungs.
(b) The capillaries are so narrow that red blood cells move through them in a single file.
(c) Actual gaseous exchange between O2 and CO2 occurs here.
g. Law of gaseous diffusion - this law states that a gas moves from an area of high pressure to an area of lower pressure.
h. Blood gas exchange.
(1) When O2 reaches the alveoli, it crosses a thin cellular barrier and moves into the capillary to reach the RBC. As the O2 enters the alveoli, it has a partial pressure (PO2) of about 100mm/Hg. Within the blood the PO2 of the venous blood is about 40mm/Hg. As the blood flows through the capillary the O2 moves from the area of high pressure within the alveoli to the area of lower pressure within the blood. Thus O2 saturation of RBCs takes place.
(2) CO2 diffuses from the blood to the alveoli in the same manner. The PCO2 in the venous blood is around 46mm/Hg in the alveoli. As the blood moves through the capillaries, the CO2 moves from the high PCO2 in the capillaries to an area of lower PCO2 in the alveoli. The CO2 is then exhaled during the next passive phase of respiration (exhalation).
NOTE: The exchange of O2 and CO2 between tissue and capillaries occurs the same as it does between the alveoli and capillaries.
(3) The amount of O2 transferred across the alveolar-capillary membrane into the blood depends primarily on the alveolar pressure of O2 in relation to the venous pressure of O2. O2 transport in the blood is a pressure dependent phenomena.
(4) This pressure differential is critical to the crew member because O2 saturation in the blood decreases as altitude increases due to the decreasing partial pressure of oxygen in the atmosphere.
(5) This decrease in O2 saturation can lead to hypoxia.
E. ENABLING LEARNING OBJECTIVE (ELO) # 5:
ACTION: Match the types of hypoxia with their respective causes.
CONDITION: Given a list of hypoxia types and a list of hypoxia causes.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Hypoxia - Definition - a condition that results from an insufficient amount of oxygen (O2) in the body.
b. Types of hypoxia: Hypemic, Stagnant, Histotoxic, and Hypoxic.
(1) Hypemic hypoxia - caused by a reduction in the O2-carrying capacity of the blood. Anemia and blood loss are the most common cause of this type. Carbon monoxide from smoking and exhaust fumes are potentially dangerous to the aviator. Nitrates, and sulfa drugs also cause this type by forming compounds with hemoglobin that block its ability to attach O2 for transport.
(2) Stagnant hypoxia - reduction in systematic blood flow or regional blood flow. Such conditions as heart failure, shock and the venous pooling of blood encountered during positive-G maneuvers predispose the individual to stagnant hypoxia. In addition, environmental extremes, prolonged sitting and restrictive clothing can produce local stagnant hypoxia.
(3) Histotoxic hypoxia - results when there is interference with the use of O2 by body tissues. Alcohol, narcotics, carbon monoxide and certain poisons such as nicotine and cyanide interfere with the cells' ability to use an otherwise adequatesupply of O2.
NOTE: Carbon monoxide is a very dangerous chemical composition as it attacks the body’s blood and tissues simultaneously. Hemoglobin has an affinity for CO3 200 times greater than O2.
(4) Hypoxic hypoxia - occurs when there is insufficient O2 in the air that is breathed or when conditions prevent the diffusion of O2 from the lungs to the blood stream. This is the type that is most likely to be encountered at altitude. It is due to the reduction of the PO2 at high altitudes. See the chart in paragraph d under ELO #2.
c. Signs and symptoms.
(1) Symptoms are observable by the individual air crew member in themselves. They vary from one person to the next, and are therefore considered subjective in nature. Examples include, but are not limited to the following:
(a) Air hunger or breathlessness.
(b) Apprehension (anxiety).
(c) Fatigue.
(d) Nausea.
(e) Headache.
(f) Dizziness.
(g) Hot and cold flashes.
(h) Euphoria.
(i) Belligerence (anger).
(j) Blurred vision.
(k) Tunnel vision.
(l) Numbness.
(m) Tingling.
(n) Denial.
NOTE: Each person will usually experience similar symptoms each time hypoxia occurs. This is why the altitude chamber is an excellent training aid.
(2) Signs are observable by the other air crew members and therefore, are considered objective in nature. Examples include but are not limited to the following:
(a) Increased rate and depth of breathing.
(b) Cyanosis.
(c) Mental confusion.
(d) Poor judgment.
(e) Loss of muscle coordination.
(f) Unconsciousness.
(g) Slouching.
d. Stages of hypoxia - indifferent, compensatory, disturbance, and critical.
(1) Indifferent stage.
(a) Altitude - sea level to 10,000 feet (equivalent altitude with 100% O2 - 34,000 to 39,000 feet) with ambient barometric pressure.
(b) Symptom - only significant effect of mild hypoxia in this stage is that night vision deteriorates at about 4,000 feet. The retina of the eye and the central nervous system have a great requirement for oxygen. To begin compensating for this your heart and breathing rate increase at about 4000 feet to improve circulation to brain and heart.
(c) Decrease of visual sensitivity of up to 28% at 10,000 feet, varying among individuals.
(d) Hemoglobin saturation - 98% at sea level decreasing to 87% at 10,000 feet.
NOTE: Symptoms of hypoxia become evident at 87% hemoglobin saturation.
(2) Compensatory stage. The circulatory system, and to a lesser degree, the respiratory system, provide some defense against hypoxia in this stage. Pulse rate, systolic blood pressure, circulation rate, and cardiac output increase.
(a) Altitude--10,000 feet to 15,000 feet (equivalent altitude with 100% O2 - 39,000 feet to 42, 000 feet) with ambient barometric pressure.
(b) Symptoms.
1. Impaired efficiency.
2. Drowsiness.
3. Poor judgment.
4. Decreased coordination.
CAUTION: Failure to recognize symptoms and take corrective action may result in an aircraft mishap.
(c) Hemoglobin saturation - 87% to 80%.
(3) Disturbance stage. In this stage, the physiological responses can no longer compensate for the O2 deficiency.
(a) Altitude - 15,000 feet to 20,000 feet (equivalent altitude with 100% O2 - 42,000 feet to 44,800 feet) with ambient barometric pressure.
(b) Symptoms.
1. Sensory.
a. Vision - peripheral and central vision are impaired and visual acuity is diminished.
b. Touch and pain - diminished or lost.
c. Hearing - one of the last senses to be lost.
2. Mental - intellectual impairment is an early sign that often prevent an individual from recognizing disabilities.
a. Memory.
b. Judgment.
c. Reliability.
d. Understanding.
3. Personality - may be a release of basic personality traits and emotions as with alcohol intoxication.
a. Happy drunk.
b. Mean drunk.
4. Performance (psychomotor functions).
a. Coordination.
b. Flight control.
c. Speech.
d. Handwriting.
e. Decision making/problem solving.
CAUTION: Failure to recognize symptoms and take corrective action may result in an aircraft mishap.
(c) Signs.
1. Hyperventilation.
2. Cyanosis.
(d) Hemoglobin saturation - 65-80%.
(4) Critical stage. Within 3 to 5 minutes, judgment and coordination deteriorate.
(a) Altitude - 20,000 feet and above (equivalent altitude with 100% O2 - 44,800 feet and above) with ambient barometric.
(b) Signs.
1. Loss of consciousness.
2. Convulsions.
3. Death.
(c) Hemoglobin saturation--less than 65%.
WARNING: When hemoglobin saturation falls below 65%, serious cellular dysfunction occurs; and if prolonged, can cause death.
NOTE: The factors increasing the chance of hypoxia are crucial in the academic development of the new aviator.
e. Factors modifying hypoxia symptoms.
(1) Pressure altitude - determines the PO2 in the lungs.
(2) Rate of ascent - at rapid rates, high altitudes can be reached before serious symptoms are noticed.
(3) Time at altitude (exposure duration) - usually the longer the duration of exposure, the more detrimental the effect of hypoxia. The higher the altitude, the shorter the exposure time required before hypoxia symptoms occur.
(4) Temperature - exposure to cold weather extremes reduces the tolerance to hypoxia by virtue of the increase in metabolic workload. Hypoxia may develop a lower altitudes than usual.
(5) Physical activity - when physical activity increases, the body demands a greater amount of O2. This increased O2 demand causes a more rapid onset of hypoxia.
(6) Individual factors - an individual's susceptibility to hypoxia is greatly influenced by metabolic rate, diet, nutrition, and emotions (probably most inconsistent factor).
(7) Physical fitness - an individual who is physically conditioned will normally have a higher tolerance to altitude problems than one who is not. Physical fitness raises an individual's tolerance ceiling.
(8) Self-imposed stresses - smoking and alcohol increase an individual's physiological altitude and therefore reduces their tolerance ceiling.
f. Expected Performance Time (EPT) - The time a crew member has from the interruption of the O2 supply to the time when the ability to take corrective action is lost.
(1) The EPT varies with the altitude at which the individual is flying.
ALTITUDE EPT__________
FL 500 & Above 9-12 seconds
FL 430 9-12 seconds
FL 400 15-20 seconds
FL 350 30-60 seconds
FL 300 1-2 minutes
FL 280 2½-3 minutes
FL 250 3-5 minutes
FL 220 8-10 minutes
FL 180 20-30 minutes
(2) EPT for a crew member flying in a pressurized cabin is reduced approximately one-half following loss of pressurization such as in a rapid decompression (RD).
g. Prevention of hypoxia (hypoxic).
(1) Limit time at altitude (AR 95-1).
(2) Use supplemental O2.
(3) Use pressurized cabin.
h. Treatment of hypoxia.
(1) O2.
(2) Descend to a safe altitude.
F. ENABLING LEARNING OBJECTIVE (ELO) # 6:
ACTION: Select the symptoms of hyperventilation.
CONDITION: Given a list.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Hyperventilation - Definition - an excessive rate and depth of respiration leading to abnormal loss of CO2 from the blood.
b. Causes.
(1) Emotions.
(a) Fear.
(b) Apprehension.
(c) Excitement.
(2) Pressure breathing.
(3) Hypoxia.
c. Symptoms--similar to those of hypoxia.
(1) Tingling sensations.
(2) Muscle spasms.
(3) Hot and cold sensations.
(4) Visual impairment.
(5) Dizziness.
(6) Unconsciousness.
d. Physiology (reason for symptoms).
(1) Stores of CO2 (necessary for proper pH of the body) are depleted.
(2) Alveolar gases are exchanged more rapidly during hyperventilation thus lowering PCO2 in the alveoli.
(3) CO2 from the blood diffuses rapidly into the alveoli causing the pH of the blood to increase.
e. Significance of hyperventilation.
(1) Can incapacitate a healthy crew member.
(2) Can be confused with hypoxia.
f. Prevention.
(1) Don't panic (easier said than done).
(2) Control rate and depth of respiration.
g. Corrective action.
(1) Above 10,000 feet--assume hypoxia and treat accordingly.
(a) 100% O2--if available.
(b) Descend to a safe altitude.
(2) Below 10,000 feet--assume hyperventilation and treat accordingly. Voluntary reduction in rate and depth of respiration.
ENABLING LEARNING OBJECTIVE (ELO) # 7:
ACTION: Identify the treatment of an ear or sinus trapped gas dysbarism.
CONDITION: Given a list of treatments.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Dysbarism - Definition - syndrome resulting from the effects, excluding hypoxia, of a pressure differential between ambient barometric pressure and the pressure of gases in the body.
b. Two types of dysbarism
(1) Trapped gas dysbarism.
(2) Evolved gas dysbarism.
c. Trapped gas dysbarism.
(1) Boyle's Law - The volume of a gas is inversely proportional to its pressure, temperature remaining constant.
(2) Dry gas conditions - Under dry gas conditions, the atmosphere is not saturated with moisture. Basically, under conditions of constant temperature and increased altitude, the volume of a gas expands as pressure decreases.
(3) Wet gas conditions - Gases within the body are saturated with water vapor. Under constant temperature and at the same altitude and barometric pressure, the volume of a wet gas is greater than the volume of a dry gas.
(4) Types of trapped gas disorders.
(a) Trapped gas disorders of the gastrointestinal tract.
1. Mechanism - the stomach and intestines contains gas which expands during ascent causing gas pains.
2. Prevention.
a. Watch your diet (if a crew member has difficulty relieving abdominal gas pains the diet should be adjusted to avoid gas-producing foods).
b. Avoid carbonated beverages and large amounts of water before going to altitude.
c. Don't chew gum during ascent.
d. Keep regular bowel habits.
3. Treatments.
a. Belching.
b. Passing flatus.
c. Descent to a lower altitude (if pain persists).
(b) Ear blocks (trapped gas disorders of the middle ear).
1. Mechanism.
a. As the barometric pressure is reduced during ascent, the expanding air in the middle ear is intermittently released through the eustachian tube.
b. As the inside pressure increases, the eardrum bulges until an excess pressure of approximately 12 to 15mm/Hg is reached.
c. At this time, a small bubble of air is forced out of the middle ear and the eardrum resumes its normal position.
d. During ascent, the change in pressure within the ear may not occur automatically.
e. With the increase in barometric pressure during descent, the pressure of the external air is higher than the pressure in the middle ear and the eardrum is forced inward.
f. If the pressure differential increases appreciably, it may be impossible to open the eustachian tube. The eardrum could rupture because the eustachian tube cannot equalize the pressure.
2. Prevention.
a. The most common complaint of crew members is the inability to ventilate the middle ear.
b. This inability frequently occurs when the eustachian tube or its opening is swollen shut as the result of an inflammation or infection due to a head cold, sore throat, middle ear infection, sinusitis, or tonsillitis.
c. Unless absolutely necessary, crew members with colds or sore throats should not fly.
3. Treatments - same as sinus block.
(c) Sinus blocks (trapped gas disorders of the ).
1. Mechanism.
a. Like the middle ear, sinuses can also trap gas during flight.
b. Sinuses are air-filled, relatively rigid, bony cavities lined with mucus membranes.
c. Sinuses are connected with the nose by means of one or more small openings.
d. If the openings into the sinuses are normal, air passes into and out of these cavities without difficulty and pressure equalizes.
e. If these openings become obstructed it may become difficult or impossible to equalize the pressure.
2. Prevention - avoid flying with a cold or congestion.
3. Treatment (ear/sinus block).
a. Stop descent of aircraft and attempt to clear by valsalva.
b. If the condition is not cleared, climb to altitude until cleared by pressure change or valsalva.
c. Reduce rate of descent and equalize ear/sinus frequently during descent.
(d) Barodontalgia (trapped gas disorders of the teeth).
1. Mechanism - change in barometric pressure can cause a toothache.
EXAMPLE: Air may be trapped in the tooth by recent dental work. Air under the filling material will expand during ascent causing pain.
2. Prevention--avoid flying following dental restoration or when in need of restoration.
3. Treatment - descent usually brings relief.
4. Referred pain.
a. Nerve endings for sinuses and the upper teeth are in close proximity in the maxilla.
b. On occasion, the sinuses will block but the pain will be referred to the upper teeth.
c. Condition must be treated as a sinus block.
H. ENABLING LEARNING OBJECTIVE (ELO) # 8:
ACTION: Identify the type of evolved gas dysbarism which occurs in body joints.
CONDITION: Given a list of evolved gas dysbarism.
STANDARD: IAW FM 1-301 and FM 8-2.
a. Evolved Gas Dysbarism (decompression sickness).
(1) Henry's Law - The amount of gas dissolved in a solution is directly proportional to the pressure of the gas over the solution. This is similar to gas being held under pressure in a soda bottle. When the cap is removed, the liquid inside is exposed to a lower pressure; therefore, gases escape in the form of bubbles. Nitrogen (N2) in the blood behaves in the same manner. Evolved gas disorders are also known as decompression sickness (DCS).
(2) Mechanism.
(a) Inert gases in body tissues (principally N2) are in pressure equilibrium with the same gases in the atmosphere.
(b) When barometric pressure decreases, the partial pressures of atmospheric gases decrease proportionally, leaving the tissues temporarily supersaturated.
(c) Responding to the supersaturating, the body attempts to establish a new equilibrium by transporting the excess gas volume in the venous blood to the lungs.
(d) However, this is an inefficient system of removal and could lead to an evolved gas disorder.
(3) The four types of evolved gas disorders.
WARNING: Evolved gas disorders are considered serious and medical treatment/advice must be sought immediately.
(a) Bends.
1. Occurs when the N2 bubbles become trapped in the joints. At the onset of bends, pain may be mild but it can become deep, gnawing, penetrating, and eventually intolerable.
2. Severe pain can cause loss of muscular power of the extremity involved and, if allowed to continue, may result in bodily collapse.
3. The larger joints, such as the knee or shoulder, are most frequently affected. The hands, wrists, and ankles are also common sites.
4. It may occur in several joints simultaneously and worsen with movement.
(b) Parathesia (creeps/tingles).
1. Tingling and itching sensations on the surface of the skin are the primary symptoms of parathesia. It is caused by N2 bubbles forming along the nerve tracts leading to the affected areas.
2. A mottled red rash may appear on the skin.
(c) Chokes.
1. Symptoms occurring in the thorax are probably caused by innumerable small N2 bubbles that block the smaller pulmonary vessels.
2. At first, a burning sensation is noted under the sternum. As the condition progresses, the pain becomes stabbing with deep inhalation. The sensation in the chest is similar to what one experiences after completing a 100 yard dash. Short breaths are necessary to avoid distress.
3. There is an uncontrollable desire to cough, but the cough is ineffective and nonproductive.
4. Finally, there is a sensation of suffocation; breathing becomes more shallow and the skin has a bluish coloration.
(d) CNS disorder.
1. In rare cases when aircrews are exposed to high altitude, symptoms may indicate that the brain or the spinal cord is affected by N2 bubble formation.
2. The most common symptoms are visual disturbances which vary from blind spots to the flashing or flickering of a steady light.
3. Other symptoms may be a dull-to-severe headache, partial paralysis, the inability to hear or speak, and the loss of orientation.
4. Paresthesia, or one-sided numbness and tingling, may also occur.
(4) Influential factors - evolved gas disorders do not happen to everyone who flies. Certain factors tend to increase the chance of evolved gas problems and reduce the altitude at which problems can occur.
(a) Rate of ascent - the more rapid the rate of ascent, the greater the chance that evolved gas disorders will occur; the body does not have time to adapt to the pressure changes.
(b) Altitude - below 25,000 feet symptoms are less likely to occur; above 25,000 feet they are more likely to occur.
(c) Body fat - fat has a higher nitrogen content than other body tissues. Obesity predisposes and individual to DCS 5 times greater than a healthy individual.
(d) Age - evidence suggests that individuals in their mid-thirties are more susceptible than those in their early twenties.
(e) Exercise - physical exertion during flight lowers the altitude at which evolved gas disorders occur.
(f) Duration of exposure - the longer the exposure, especially above 20,000 feet, the more likely that evolved gas disorders will occur.
(g) Repeated exposure - the more often individuals are exposed to altitude above 18,000 feet (without pressurization), the more they are predisposed to evolved gas disorders.
(5) Prevention.
(a) Denitrogenation.
(b) Pressurization of cabin.
(6) Treatment.
(a) Descend to ground level.
(b) 100% O2.
(c) Seek medical advice/assistance.
(d) Compression therapy.
(7) Aircrew restrictions.
(a) According to AR 40-8, crew members will not fly for 24 hours after SCUBA diving.
(b) During SCUBA diving, excessive nitrogen uptake by the body occurs in using compressed air.
(c) Flying at 8,000 feet within 24 hours after SCUBA diving at 30 feet subjects an individual to the same factors a non-diver faces when flying unpressurized at 40,000 feet. N2 bubbles form in the circulatory system.