lecture 4-aviation human factors. remember decompression means loss of pressurization. flying with...
TRANSCRIPT
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Lecture 4-Aviation Human Factors
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Remember
Decompression means loss of pressurization.
Flying with the aircraft that loss of pressurization will expose the crew/passengers to: Hypoxia, Hyperventilation, Decompression
sickness, Trapped gas expansion.
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Contents
Hyperventilation Trapped Gas Decompression Sickness (Evolved Gas
Disorders)
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HYPERVENTILATION
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Breathing
Breathing: process of taking air (O2)into the lung and exchanging gas (CO2)to the environment.
CO2 is the gas produce by all living cells It is important for maintaining chemical
balance and control our breathing. Removing of CO2 from the body is limited by
the lung during exhalation. When human expose to situation of
emotional stress, breathing become fast and can cause hyperventilation.
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Hyperventilation
Hyperventilation is simply a matter of rate and depth breathing increases rapidly.
It causes the excessive loss of CO2 from the blood.
This results to degrade the chemical balance in the blood.
Also can affect the brain, as the CO2 levels in the brain reduces.
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Hyperventilation
CAUSES It caused by emotional reaction such as
anxiety, fear, stress and anger.
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Hyperventilation
SYMPTOMPS Dizziness Lightheadedness Blurred Vision Numbness Tingling Hot and cold sensations. Muscle incoordination. Unconsciousness: due to respiratory systems overriding
mechanism to regain control of breathing.
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Hyperventilation & Hypoxia
Hyperventilation: Usually occurs below
10,000. Skin may look pale. As we ascend, it can
occur slowly and gradually over time.
Hypoxia: Usually occurs above
10,000. Skin may look blue
cyanosis. Can occur rapidly.
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Treatment of hyperventilation
Best method is to voluntarily reduce rate of breathing
Normal rate is 12-16 breaths per minute Avoid panic Go to 100% O2 (if available)
Talk or sing (to increase CO2 level) If severe or combined with hypoxia, return to
ground level. Breathing into a bag.
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TRAPPED GAS
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Boyle’s Law
Pressure decrease, Volume increase
Site level
10,000 feet
18,000 feet
25,000 feet
43,000 feet
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Boyle’s Law
Gases within the body are influenced by pressure and temperature changes outside the body
Ascent – pressure is decreased and gases expand.
Descent – pressure is increased and gases contract.
The body can withstand changes in total pressure as long as the air pressure within the body cavities is equalized to ambient pressure
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Trapped Gas
Body cavities most often affected Middle ear Sinuses Teeth Stomach & Intestines (Gastrointestinal
tract)
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Trapped Gas
1. Middle Ear
FRONTALS
ETHMOIDS
SPHENOID
MAXILLARY
2. Sinus
3. Stomach and
Intestines
1. Teeth
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Anatomy of Ear
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The ear is not only an organ of hearing but also one of regulating equilibrium.
When ascending to altitude, aircrew members often experience physiological discomfort during changes in atmospheric pressure.
Ear
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The Middle Ear
Ascent to altitude As ambient pressure decreases with
ascent, gas expands within the middle ear Air escapes through the Eustachian tubes
to equalize pressure As pressure increases, the eardrum bulges
outward until a differential pressure is achieved and a small amount of gas is forced out through eustachian tube and the eardrum relaxes.
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The Middle Ear
Descent to altitude Equalization of pressure does not occur
automatically Eustachian tube performs as a flap valve and allows
gas to pass outward easily, but resists the reverse. During descent the ambient pressure increase, the
flap valve can stop the returning air into the middle-ear to equalize the pressure.
If pressure is not equalized Ear block may occur and it is extremely difficult to reopen
the eustachian tube The eardrum may not vibrate normally and decreased
hearing results (minor hearing lost)
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Middle Ear Block
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Ear Block
Symptoms “Ear congestion” Ringing in the ears. Inflammation. Discomfort. Pain. Temporary
impairment of hearing
Bleeding (severe cases)
Eardrum rupture
Contributing Factors Flying with head
cold Flying with a sore
throat
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Middle Ear Discomfort
A cold can produce enough congestion around the eustachian tube to make equalization difficult.
This causes and ear block causing a build up in pressure that can be very painful.
Severe ear pain and loss of hearing that can last several hours to several days.
Can cause rupture of the ear drum Usually occurs on descent
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Ear Block Treatment
Treatment Yawning or swallowing Performing “Valsalva” Nasal sprays – best used prior to descent Pain medications For infants / children – provide a bottle /
straw to suck Ascend to safe altitude where symptoms
subside and then slowly descend
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Ear Block Prevention
Prevention DO NOT FLY WITH A HEAD COLD “Stay ahead of your ears”
Valsalva during descent
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Delayed Ear Block
Occurs in situations where crew members breath 100% oxygen at altitude, especially if oxygen was maintained during descent to ground level
Symptoms occur 2 to 6 hours after descent Oxygen in the middle ear is absorbed and
creates a decreased pressure Prevention – valsalva numerous times after
altitude exposure to prevent absorption
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Sinus
Sinus is the cavity within a bone, especially in the bones of the face.
FRONTALS
ETHMOIDS
SPHENOID
MAXILLARY
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The Sinuses
Most often involves frontal sinuses (above each eyebrow) and maxillary sinuses (both cheeks)
Sinus ducts have openings into the nasal passage
Gas escaped with increases upon ascent most often without problems
With descent, air moves back out through the ducts if they are open
If the openings are swollen, a blockage may occur.
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The Sinuses
Symptoms Severe pain Possible referred
pain to teeth
Treatment Equalize pressure as
quickly as possible Valsalva is
sometimes effective Coughing against
pressure is effective Ascent to safe
altitude then slow descent
Nasal sprays may help
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The Teeth
Air trapped within teeth expands with ascent. Pain often increases with altitude. Rarely caused by a root abscess with a small
pocket of trapped gas
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The Teeth (Barodontalgia)
Treatment / Prevention Descent Pain medications Good dental hygiene
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Gastrointestinal Tract
Gastrointestinal: related to stomach and intestines
Most frequently experienced with a rapid ascent (decrease in barometric pressure)
Symptoms result from gas expansion Above 25,000 feet distention could be
large enough to produce severe pain May produce interference with breathing
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Gastrointestinal
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Gastrointestinal Tract
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Sources of Gas Swallowed air (including
gum chewing) Food digestion Carbonated beverages
Treatment Walking or moving Massage the affected
area Loosen restrictive
clothing Use of a gas reducing
agent Descent to a higher
pressure
Gastrointestinal Tract
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DECOMPRESSION SICKNESS
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Henry’s Law
Nitrogen dissolved in the blood responds in same way.
Carbonated drink: Once the seal is opened, the gas that has been under pressure escapes, gas that has been dissolved in the drink also begins to escape by forming bubbles.
Henry’s Law: Pressure of gas decrease, the gas in the in the
liquid also decrease.
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Decompression sickness
Decompression sickness is caused by nitrogen forming as bubbles in the blood.
As pressure decreases, gases (nitrogen) dissolved in body fluids are released as bubbles.
Can occur in the blood, other fluids, or in the tissues
This sickness refer to the nitrogen saturation of the body.
This is related to the inefficient removal and transport of the expanded nitrogen gas volume from the tissues to the lungs.
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Remember
Composition of gas in atmosphere consists of: 78% nitrogen, 21% oxygen and 1% are amounts of other gases.
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Decompression sickness
Tissues and fluid of the body contain from 1 to 1.5 litres of dissolved nitrogen, depending on the pressure of nitrogen in the surrounding air.
As altitude increases, the partial pressure of
atmospheric nitrogen decreases and nitrogen leaves the body to re-establish equilibrium. If the change is rapid, recovery of equilibrium lags, leaving the body supersaturated.
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Decompression Sickness
Type I (Non-Serious) Bends Skin Manifestations
Type II (Serious) Chokes Neurological Manisfestations
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The Bends Generally located around / near
articulating joints of the body Pain from mild to unbearable Factors of exercise, increased altitude,
and increased time of exposure will increase severity of symptoms
Descent to below altitude of onset
Decompression Sickness (DCS)
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Decompression Sickness (DCS)
Skin manifestations Mild Tingling of the skin Believed to be caused by bubbles of gas evolving
under the skin Symptoms themselves are not serious
HOWEVER they are a WARNING that bubbles may form elsewhere
Continued exposure may lead to more serious forms of decompression sickness
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The Chokes Rare but potentially life-threatening Nitrogen bubbles in the blood vessels of the lungs Symptoms
Deep and sharp pain or burning sensation under the sternum
Shortness of breath Dry, progressive, nonproductive cough Feeling of suffocation with decreasing ability to take a
breath Results in hypoxia
Decompression Sickness (DCS)
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Decompression Sickness (DCS)
Neurologic Manifestations (CNS) Very rare Rarely may effect brain or spinal cord More common
Visual disturbances (blind spots, flushing, or flickering vision – Scotoma)
Persistent headache Partial paralysis Inability to speak or hear Loss of orientation
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Factors Affecting DCS
Scuba divingHydration level Repeated exposuresLength of time at altitudeRate of ascentAltitude (18,000ft)
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Severity and Rapidityof Onset Related to
Rate of ascent More rapid = sooner symptoms appear
Altitude Below 25,000 feet is rare Above 25,000 feet may occur after leveling off
Duration of exposure Physical activity
Exercise lowers the threshold for manifestations, particularly the bends
Individual susceptibility Unpredictable
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SCUBA Diving
Greatly lowers threshold altitude for the occurrence of decompression sickness when flying
Cases of decompression sickness have occurred in individuals who fly in cabins as low at 5,000 feet If within 6 hours of diving Recommended at least 24-hour delay
between diving with SCUBA and flying
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Decompression Sickness (DCS)
Emergency Treatment 100% oxygen for everyone onboard Declare an emergency Descent as rapidly as possible Immobilize affected areas Treat shock Land as soon as possible Medical evaluation by a QUALIFIED flight
surgeon / hyperbaric physician ASAP Decompression chamber therapy if required
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Prevention
In high-altitude flight, aircrews can be protected against decompression sickness.
Protective measures include: De-nitrogenation. Cabin pressurization. Limitation of time at high altitude. Aircrew restrictions.
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