Ventilation and Diffusion

Question 1

What is atmospheric pressure? (at sea level)

Answer 1

760mmHg or 101.325 kPa

Question 2

What is partial pressure

Answer 2

The pressure a gas would exert if it occupied the volume of space on its own

Question 3

What percentage of the air is nitrogen?

Answer 3

78.08% (593mmHg)

Question 4

What percentage of the air is oxygen?

Answer 4

20.95% (159mmHg)

Question 5

What percentage of air is CO2?

Answer 5

0.039% (0.29mmHg)

Question 6

What will happen to partial pressure when underwater?

Answer 6

It will increase the deeper you are

Question 7

What can be used to replace high levels of oxygen?

Answer 7

• Trimix: nitrogen-oxygen-helium

- Heliox: Oxygen and helium

Question 8

What does Henry’s law relate to?

Answer 8

Gases dissolving into and out of the plasma

Question 9

How will the gas move if the partial pressure in the liquid is higher than in the air?

Answer 9

The gas will move out of the liquid

Question 10

What is the most soluble gas?

Answer 10

CO2

Question 11

How much more soluble is CO2 in the blood than Oxygen?

Answer 11

20x more

Question 12

How much N2 is in the blood at atmospheric pressure and why?

Answer 12

Negligble amounts because it is very poorly soluble

Question 13

What does the total amount of gas in the liquid include?

Answer 13

The amount dissolved in solution plus what is dissolved and chemically bound in solution (e.g bicarbonate)

Question 14

What differences are there in composition between the atmospheric air and alveolar air?

Answer 14

• O2 is lower (104 mmHg)
• CO2 is higher (40mmHg)
• Water vapour is higher
• Proportion of N2 is lower

Question 15

What is the water vapour pressure?

Answer 15

47 mmHg

Question 16

What is the rate of diffusion of oxygen proportional to?

Answer 16

• Surface area
• Solubility
• Concentration gradient (difference in partial pressure)
• Inversely to tissue thickness
• Inversely to sqroot molecular mass

Question 17

What is the surface area of the lungs?

Answer 17

50 - 100 m^2

Question 18

How many alveoli are there on average?

Answer 18

500 million

Question 19

What is the thickness of the alveoli?

Answer 19

0.2 - 0.5 um

Question 20

What is the conc difference of O2 between the venous blood and alveolar air?

Answer 20

104 mmHg and 40 mmHg

64 mmHg

Question 21

How quickly does it take at rest for blood to pass through pulmonary capillaries?

Answer 21

1 second

Question 22

What is the difference in concentration of PCO2 in alveoli and venous blood?

Answer 22

• 40 mmHg in alveoli

- 45 mmHg in venous blood

Question 23

What must the gas go through in order to reach the blood?

Answer 23

• Must dissolve in aqueous layer
• Must diffuse across the membrane
• Must enter the blood

Question 24

What can reduce gas exchange as a result of decreasing surface area?

Answer 24

Emphysema

Question 25

What increases the thickness of respiratory membranes which can reduce gas exchange?

Answer 25

Pulmonary oedema

Question 26

How does gas move in the tissues?

Answer 26

• Partial pressure gradients are reversed
• Movement if gases in opposite direction than in the lungs
• CO2 moves into blood from tissues
• O2 moves out of blood from tissues

Question 27

How does increased altitude affect the gas exchange?

Answer 27

• PO2 is reduced
• Increase in release of EPO
• Hb levels increase

Question 28

How much does atmospheric pressure increase by every 10m in depth?

Answer 28

760 mmHg (1 atmosphere)

Question 29

Name some of the problems associated with N2 bubbles?

Answer 29

• Can form lethal emboli
• Bubbles in the pulmonary circulation
• In joints - extremely painful
• In brain - stroke
• Decompression sickness

Question 30

What can rapid ascension without exhaling cause?

Answer 30

• Atmospheric pressure decreases when coming up to surface
• Volume of air in lungs increases
• Causes rupture of alveoli and gas bubbles enter circulation (arterial gas embolism)
• Usually lodge in cerebral circulation
• Can cause seizures, fits, unconsciousness etc.