Physiology

Question 1

What atmospheric characteristics create challenges to survival at high altitudes?

Answer 1

Air Temperature
Humidity
Air Density 
Oxygen Availability 
Solar Radiation

Question 2

At what temperature rate does a parcel of air cool through adiabatic cooling?

Answer 2

0.65 degrees per 100m or 26 degrees per 4000m

Sea level - 15 degrees

4000m (13123ft) - minus 11 degrees

Question 3

What is the temperature and altitude of the Tropopause.

Answer 3

-56.6 degrees in ISA
average of 36000 ft in ISA
(20000ft over the poles and 60000ft over equator)

Question 4

What are the layers of the atmosphere and what level do they occur

Answer 4

Toposphere - 0 to 36000ft
Tropopause - 36000 to 50000ft
Stratosphere - 50000 to ……

Question 5

What is Humidity

Answer 5

Water vapour suspended in air, present in a gaseous state and not normally visible to the naked eye.

Question 6

What is relative humidity?

Answer 6

The amount of water vapour present compared to the total amount of water vapour the same volume of air can hold at a given temperature, expressed as a percentage.

Question 7

What is the relationship between relative humidity and altitude?

Answer 7

As altitude increases, relative humidity decreases due to the reduction in temperature and air density.

Question 8

What are the effects of low humidity?

Answer 8

Dry or cracked skin
lining of the nasal passage to dry and become susceptible to Rhinoviurs and nose bleeds
Respiratory discomfort
Aggravated allergens in some individuals
Fatigue and low levels of alertness due to dehydration
Drying eyes

These can be similar to the effects at a high humidity. Continue to consume water and keep well hydrated

Question 9

What gasses make up the earths atmosphere?

Answer 9

78. 08% Nitrogen
79. 95% Oxygen
80. 93% Argon
81. 04% Other gasses

Question 10

What is Boyles law

Answer 10

Pressure/Volume at a constant Temp

Increase in pressure = Decrease in Volume

Question 11

Charles Law

Answer 11

Temperature/Volume at a constant Pressure

Increase in Volume = Increase in Temperature

Question 12

Gay-Lussac Law

Answer 12

Pressure/Temperature at a constant volume

Increase in Pressure = Increase in Temperature

Question 13

What happens to Density with the increase in altitude?

Answer 13

As altitude increase density decrease due to the reduction temperature and weight of the air above it.
We assume it is Linear for ease of calculation but in reality the earths atmosphere is not an ‘Ideal Gas’ hence the variable density and temperature.

Question 14

What is the % of Oxygen at 45000ft?

Answer 14

20.95%
It doesn’t change, due to there being very little ‘weight’ of all the air above it, the partial pressure of the air at 45000ft is low and its ability successfully complete gas exchange within our lungs is decreased.

Question 15

At what altitude has the atmospheric pressure and inspired oxygen pressure reduced to 50% of its sea level value?

Answer 15

50% effectiveness = 5500m or 18050ft

30% effectiveness = 8900m or 29200ft

It is almost a linear decrease with altitude.

Question 16

What is Time of Useful Consciousness (TUC)?

Answer 16

The elapsed time from an interruption of normal air supply or exposure to an oxygen poor environment until the time when the ability to function is likely to be lost. At this point an affected individual would no longer be capable of taking normal corrective or protective action.
It is not the time to unconsciousness!

Question 17

At what altitude does casa require a pilot to be on 100% oxygen and secured in the pilot seat at all times?

Answer 17

45000ft

Question 18

What is more dangerous, a rapid decompression or a gradual decompression?

Answer 18

They are both dangerous for different reasons.
Rapid - commands immediate attention as the TUC will short at high altitudes.
Gradual - TUC will slowly decrease as cabin altitude increases. If the decompression goes unnoticed it can be equally as dangerous as the TUC runs out.

Question 19

What is the TUC at 25000ft, 30000ft, 35000ft 40000ft, 45000ft?

Answer 19

25000ft = 3 - 5mins or 1.5 - 2.5min post rapid decompression

30000ft = 1 - 2mins or 30sec - 1min post rapid decompression

35000ft = 30sec - 1min or 15 - 30sec post rapid decompression

40000ft = 15 - 20sec or nominal post rapid decompression

45000ft = 9 - 12 sec or nominal post rapid decompression

Question 20

What factors effect an individuals TUC?

Answer 20

• Total lung surface area for gas exchange (smoking can cause mucus to form in the lungs, reducing the surface area resulting in reduce performance)
• Total Haemoglobin available in the blood to bind the oxygen (smoking can cause the haemoglobin to carry carbon monoxide resulting in reduce performance)
• Oxygen consumption rate at rest (relating to body mass index)
• The ability to extract oxygen from the blood (genetic)
• Physical activity at altitude (will reduce TUC as you use oxygen faster)
• Fatigue (reduces bodies resistance to hypoxia)
• Diet (the brain feeds from glucose/blood sugar. If blood sugar is low/hypoglycaemic, the brain is predisposed to hypoxia)
• Alcohol (blood alcohol level induces a hypoxic state, a state which is rapidly elevated with increased altitude)
• Medications (some cause cells not to utilise oxygen effectively)
• smoking, poor physical health and illness decrease the TUC

Question 21

What is relative humidity?

Answer 21

The amount of water vapour present compared to the total amount of water vapour the same volume of air can hold at a given temperature, expressed as a percentage.