Lecture 4-Aviation Human Factors. Remember Decompression means loss of pressurization. Flying with the aircraft that loss of pressurization will expose.

Lecture 4-Aviation Human Factors

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.

Contents

Hyperventilation Trapped Gas Decompression Sickness (Evolved Gas

Disorders)

HYPERVENTILATION

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.

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.

Hyperventilation

CAUSES It caused by emotional reaction such as

anxiety, fear, stress and anger.

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.

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.

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.

TRAPPED GAS

Boyle’s Law

Pressure decrease, Volume increase

Site level

10,000 feet

18,000 feet

25,000 feet

43,000 feet

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

Trapped Gas

Body cavities most often affected Middle ear Sinuses Teeth Stomach & Intestines (Gastrointestinal

tract)

Trapped Gas

1. Middle Ear

FRONTALS

ETHMOIDS

SPHENOID

MAXILLARY

2. Sinus

3. Stomach and

Intestines

1. Teeth

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

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.

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)

Middle Ear Block

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

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

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

Ear Block Prevention

Prevention DO NOT FLY WITH A HEAD COLD “Stay ahead of your ears”

Valsalva during descent

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

Sinus

Sinus is the cavity within a bone, especially in the bones of the face.

FRONTALS

ETHMOIDS

SPHENOID

MAXILLARY

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.

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

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

The Teeth (Barodontalgia)

Treatment / Prevention Descent Pain medications Good dental hygiene

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

Gastrointestinal

Gastrointestinal Tract

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

DECOMPRESSION SICKNESS

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.

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.

Remember

Composition of gas in atmosphere consists of: 78% nitrogen, 21% oxygen and 1% are amounts of other gases.

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.

Decompression Sickness

Type I (Non-Serious) Bends Skin Manifestations

Type II (Serious) Chokes Neurological Manisfestations

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)

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

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)

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

Factors Affecting DCS

Scuba divingHydration level Repeated exposuresLength of time at altitudeRate of ascentAltitude (18,000ft)

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

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

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

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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