LECTURE 4TRAPPED GAS AND DECOMPRESSION

SICKNESSAviation Human Factors

Review on Last Chapter

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.

Introduction

Human physiology is evolutionary adapted to be efficient up to 12,000ft above sea level.

Outside this zone, physiological compensatory mechanism may not be able to cope with the stresses altitude.

Besides hypoxia, the changes in pressure will result in air or flight sickness which are: Trapped Gas Decompression Sickness (Evolved Gas

Disorders)

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

Ascend – pressure is decreased and gases expand.

Descend – 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

Boyle’s Law

Trapped Gas

Trapped gas means the gas can’t be released especially by our body cavities part.

Our body cavities that often experienced trapped gas are: Middle ear Sinuses Teeth Stomach & Intestines (Gastrointestinal

tract)

Trapped Gas

1. Middle Ear

FRONTALS

ETHMOIDS

SPHENOID

MAXILLARY

2. Sinus

4. Stomach and

Intestines

3. Teeth

Anatomy of Ear

Anatomy of Ear

Ear12

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.

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.

Trapped Gas Expansion

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)

Ear Block

Processes: How middle ear is affected when a person is flying into higher altitude Middle ear is on of the part of body

cavities that being affected by the trapped gas.

When the aircraft ascent to high altitude, the atmospheric pressure drop causing the gases within the body to expand.

The expanded gas escape from body through the Eustachian tube located at middle ear to equalize the pressure.

The eardrum will bulge outwards to allow the gases escape from the body until the differential of the pressure is achieved and then back to it form after several force that push the gasses outward to achieve the equilibrium.

When the aircraft descend, the sudden change of increasing of atmospheric pressure will force the gasses within the body to contract.

Processes: How middle ear is affected when a person is flying into higher altitude

This will cause the body lose it equilibrium because the pressure outside the body is higher than within the body.

One way to achieve it is that, the gasses will be push through Eustachian tube.

Since Eustachian tube act like a flap valve, it will function to prevent the gasses from losing.

If the Eustachian tube is blocked , the middle ear block will happen and it is extremely difficult to re-open the Eustachian tube.

The person will feel uncomfortable and pain.

Processes: How middle ear is affected when a person is flying into higher altitude

Ear Block – Contributing Factor Contributing Factors

Flying with head cold 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.

Flying with a sore throat

Ear Block - Symptoms

Symptoms “Ear congestion” Ringing in the ears. Inflammation. Discomfort. Pain Temporary impairment of hearing Bleeding (severe cases) Eardrum rupture

Middle Ear Discomfort

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 more critical during descent compare to ascend.

Ear Block Prevention

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

Valsalva during 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

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

Like the middle ear, sinuses can also trap gas during flight.

The sinuses are air-filled, relatively rigid, bony cavities lined with mucous membranes.

They connect with the nose by means of one or more small openings.

The two frontal sinuses are within the bones of the forehead; the two maxillary sinuses the two ethmoid sinuses

If the openings into the sinuses are normal, air passes into and out of these cavities without difficulty and pressure equalizes during ascent or descent.

Swelling of the mucous membrane lining, caused by an infection or allergic condition, may obstruct the sinus openings

These conditions may make it impossible to equalize the pressure.

The Sinuses

Change of altitude produces a pressure differential between the inside and the outside of the cavity, sometimes causing severe pain.

The Sinuses

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

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

DECOMPRESSION SICKNESS

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.

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.

Remember

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

Decompression Sickness

Type I (Non-Serious) Bends Skin Manifestations

Type II (Serious) Chokes Neurological Manisfestations

Decompression Sickness (DCS) The Bends (Pain in large joints)

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

Decompression Sickness (DCS) Skin manifestations

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

Decompression Sickness (DCS) 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 Feeling of suffocation with decreasing ability to take a

breath Results in hypoxia

Decompression Sickness (DCS) Neurologic Manifestations

Very rare Rarely may effect brain More common

Visual disturbances (blind spots) Persistent headache Partial paralysis Inability to speak or hear Loss of orientation

Factors Affecting DCS

Scuba divingRepeated exposuresLength of time at altitudeRate of ascentAltitude (18,000ft)

Severity and Rapidity of 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

Prevention50

In high-altitude flight, aircrews can be protected against decompression sickness.

Protective measures include: Cabin pressurization. Limitation of time at high altitude.

Quick notes about evolved gas disorders

Rate of ascent, altitude, body fat, exercise, duration and repeated exposure are factors that increase the risk of having an evolved gas disorder

pressurized cabins and denitrogenation are recommended for prevention

if it occurs, get the individual to ground level immediately, give him 100% O2 seek medical attention and compression therapy

Summary

Trapped Gas: Expanding gases within the body cannot escape to allow the equalization of body pressures.

Decompression Sickness: Occurs when gases dissolved in body fluids are released as bubbles.