Lecture 4 Trapped gas and decompression sickness

1. Lecture 4Trapped 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. Boyle’s Law 43,000 feet PRESSURE DECREASE, VOLUME INCREASE 25,000 feet 18,000 feet 10,000 feet Site level

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 bodycavities that often experienced trapped gas are: • Middle ear • Sinuses • Teeth • Stomach & Intestines (Gastrointestinal tract)

9. FRONTALS ETHMOIDS SPHENOID MAXILLARY Trapped Gas 2. Sinus 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

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. FRONTALS ETHMOIDS SPHENOID MAXILLARY Sinus • 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 ethmoidsinuses

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 • 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.

39. 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.

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

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.