Trapped Gas and Decompression Sickness

Question 1

What are the 2 aircraft pressurization techniques? Give an aircraft for both

Answer 1

Isobaric Control (constant value over altitudes, C-17)
Differential Control (>23,000 ft 5 psid difference, Oxygen mask at all times, CF-18)

Question 2

What cabin altitude is maintained by most transport and commercial aircraft?

Answer 2

6,000-8,000ft

Question 3

What is one advantage and disadvantage of aircraft pressurization?

Answer 3

Pro: Reduce risk of hypoxia/DCS
Con: Increased weight reduces efficiency

Question 4

What are two types of decompression?

Answer 4

Rapid (loud, 2-15 seconds, compounds hypoxia effect)
Slow (insidious, difficult to notice)

Question 5

What is Boyle’s Law?

Answer 5

Volume of a gas is inversely proportional to pressure (balloon becomes bigger as we rise in altitude, less pressure means more gas moves around)

Question 6

What are 3 factors determining decompression rate?

Answer 6

Cabin volume (large cabin takes longer)
Orifice area (bigger hole, faster decompression)
Pressure ratio (between cabin and outside air)

Question 7

What are 4 physical indications of decompression?

Answer 7

Loud noise
Drop in temperature
Objects moving around, may depart
Fog

Question 8

Rapid Decompression can shorten EPT by _________

Answer 8

1/3 to 1/2 (so 3-5 mins can suddenly become ~1-2)

Question 9

Why is slow decompression so dangerous?

Answer 9

It is insidious

Question 10

What are 5 areas in the body affected by Trapped Gas?

Answer 10

Gastrointestinal
Ears
Sinuses
Teeth
Lungs

Question 11

If you experience pain on descent, what maneuver can you do?

Answer 11

Valsalva manuever

Question 12

If you experience pain on ascent, what maneuver should you NOT do?

Answer 12

Valsalva maneuver

Question 13

What are the 3 maneuvers?

Answer 13

Valsalva (most effective), Toynbee, Frenzel

Question 14

What is the Valsava maneuver?

Answer 14

Pinch your nose and try to blow through it (with HA/LP mask, close right port and cough)

Question 15

What law governs Decompression Sickness?

Answer 15

Henry’s Law

Question 16

What is Henry’s Law?

Answer 16

Amount of gas in a solution varies with partial pressure (opening a carbonated beverage, the gases get excited and exit, making a hissing sound)

Question 17

Are Trapped Gas and DCS the same thing?

Answer 17

No, Trapped Gas is gas stuck inside (compression) whereas DCS is gas unable to leave (forming nitrogen bubbles in body)

Question 18

What is the most common symptom of DCS?

Answer 18

The Bends, 80%, affects joint or muscle pain

Question 19

What factors affect DCS?

Answer 19

• Altitude (18,000 ft)
• Level of activity (moving around)
• Exposure time

Question 20

What are prevantative measures to DCS

Answer 20

• Denitrogenation (Pre-breathe, have 100% O2 for a while)
• Aircraft pressurization

Question 21

T or F: If you experience DCS, any airfield is good to land at

Answer 21

False, land at the nearest airfield with a Hyperbaric Treatment chamber

Question 22

What are 3 ways to treat DCS?

Answer 22

• Descend as soon as practical
• 100% Oxygen (stay on)
• Hyperbaric treatment