1. Lecture 4 Trapped gas and decompression sickness
Aviation Human Factors

2. 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.

3. 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)

4. TRAPPED GAS

5. PRESSURE DECREASE, VOLUME INCREASE
Boyle’s Law
43,000 feet
25,000 feet
18,000 feet
10,000 feet
Site level
PRESSURE DECREASE, VOLUME INCREASE

6. 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

7. Boyle’s Law

8. 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)

9. 4. Stomach and Intestines
Trapped Gas
2. Sinus
FRONTALS
ETHMOIDS
SPHENOID
MAXILLARY
1. Middle Ear
3. Teeth
4. Stomach and Intestines

10. Anatomy of Ear

11. Anatomy of Ear

12. Ear
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.

13. 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.

14. Trapped Gas Expansion

15. 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)

16. Ear Block

17. 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.

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

19. 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.

20. 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

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

22. 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.

23. Ear Block Prevention Prevention DO NOT FLY WITH A HEAD COLD
“Stay ahead of your ears”
Valsalva during descent

24. 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
Valsalva…
Yawn, Chew, Swallow
Slow descent rate
Post Flight Ear Block:
Caused by absorbsion of O2 within the middle ear
TREATMENT = Frequent Valsalva

25. 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

26. Sinus
FRONTALS
ETHMOIDS
SPHENOID
MAXILLARY
Sinus is the cavity within a bone, especially in the bones of the face.

27. 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

28. The 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.

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

30. The Sinuses Symptoms Treatment 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

31. 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

32. The Teeth (Barodontalgia)
Treatment / Prevention
Descent
Pain medications
Good dental hygiene

33. 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

34. Gastrointestinal

35. Gastrointestinal Tract

36. 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

37. DECOMPRESSION SICKNESS

38. 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.
When the atmospheric pressure is decreased rapidly to certain critical values, the nitrogen pressure gradient between the body and the outside air is such that nitrogen will come out of solution in the form of bubbles
Can occur in the blood, other fluids, or in the tissues
Symptoms do not appear rapidly

39. Henry’s Law
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.
Nitrogen dissolved in the blood responds in same way.

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

41. Decompression Sickness
Type I (Non-Serious)
Bends
Skin Manifestations
Type II (Serious)
Chokes
Neurological Manisfestations

42. 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

43. 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

44. 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

45. 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

46. Factors Affecting DCS Scuba diving Repeated exposures
Length of time at altitude
Rate of ascent
Altitude (18,000ft)

47. 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
Time at altitude.
The longer one is at an excessive altitude, the greater the risk for developing DCS because more bubbles can form and be transported throughout the body.
Rate of ascent.
The more rapid the ascent, the greater the chance of bubble formation because the body has little time to equalize the pressure changes.
Altitude.
4. Age and obesity.
Older people tend to be more susceptible to DCS under minimal conditions. The same is true for obese people whose fat will store more gas and nitrogen. It is also suspected that recent alcohol use can increase the risk.
6. Repeated exposure.
Taking several flights over a short period of time (48 hours) increases the chances of problems. Repeated physiological “insults” to affected organs make them more susceptible.
The threshold for developing DCS problems is usually above 18,000 feet. Increases more rapidly above 26,000 feet.

48. 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

49. 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

50. Prevention
In high-altitude flight, aircrews can be protected against decompression sickness.
Protective measures include:
Cabin pressurization.
Limitation of time at high altitude.

51. 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

52. 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.