Physical Principles of Gas Exchange

Question 1

Composition of air

Answer 1

79 nitrogen 600mmHg
21 oxygen 160mmHg
1atm= 760mmHg

Question 2

Rate of net diffusion is determined by ___

Answer 2

Difference in partial pressures
If pp of gas in alveoli> blood, gas goes into blood
If pp of gas in blood> alveoli, gas moves into alveoli

Question 3

Vapor pressure of water from humidified airways

Answer 3

47mmHg when gas mixtures is fully humidified at 37 C
Thus, 47mmHg due to water, so airway- 713mmHg is air, thus 713x.21= 150mmHg

Question 4

Factors which affect gas diffusion rates

Answer 4

Pressure differences
Gas solubility
Area of fluid
Distance which must be diffused across
Molecular weigh
Temperature of fluid

Question 5

Graph of gas removal X and Y axis

Answer 5

X- time
Y- concentration of gas
Slopes down like a 1/4 circle

Question 6

How much gas does normal ventilation remove?

Answer 6

1/2 in 17 seconds

Question 7

Temperature effect on solubiltiy

Answer 7

Lower temp- gas goes more into fluid

Question 8

1/2 normal ventilation removes __ gas in 34 seconds

Answer 8

1/2 (2x slower than normal ventilation)

Question 9

Twice normal ventilation removes ___ gas in 8 seconds

Answer 9

1/2 (compared to normal which removes 1/2 gas in 17 seconds)

Question 10

Normal alveolar PO2

Answer 10

100mmHg

Question 11

Normal PCO2

Answer 11

40mmHg

Question 12

When is alveolar air expired?

Answer 12

End of exhalation- its the furthest!

Question 13

Factors that affect rate of gas diffusion through respiratory membrane

Answer 13

Thickness of respiratory membrane (increased thickness significantly intereferes with respiratory exchange)
Surface area of respiratory membrane (direct correlation)
Diffusion coefficient (of any given molecule like oxygen, co2, nitrogen)
Pressure difference across respiratory membrane

Question 14

What does emphysema do to alveoli?

Answer 14

Decreases surface area by 5x, significantly decreases rate of gas diffusion

Question 15

Diffusing Capacity

Answer 15

The ability to gas exchange between alveoli and pulmonary blood in quantitative terms

Question 16

Diffusing capacity for Oxygen and CO2

Answer 16

O2- 21ml/min/mmHg (max 65)
CO- 17
CO2- 400 (max 1200)

Question 17

Carbon monoxide method

Answer 17

Measuring of Carbonmonoxide used to calculate O2 diffusing capacity
Partial pressure of CO measured in alveolar gas sample
CO binds tightly to hemoglobin (blood partial pressure = Zero)
Pressure difference of CO = alveolar partial pressure
Diffusing capacity of CO converted to O2 by multiplying by factor of 1.23

Question 18

O2 consumption in body

Answer 18

250ml/minute
1L of o2 per 4 minutes

Question 19

Deoxygenated blood PO2 and PCO2

Answer 19

40
45

Question 20

Alveolar gas partial pressures when V/Q= infinity

Answer 20

PO2 150
CO2 0

Question 21

inspired air composition

Answer 21

PO2 150
CO2 0

Question 22

Venous blood composition at pulmonary capillary

Answer 22

PO2 40
PCO2 45

Question 23

Normal alveolar partial pressures (inspired air + blood)

Answer 23

alveolar PO2 100
Alveolar PCO2 40

Question 24

Pulmonary arteries PP

Answer 24

O2 40
CO2 46

Question 25

Pulmonary veins PP

Answer 25

Equals pulmonary vein pressures
O2 100
CO2 40

Question 26

VQ in shunts

Answer 26

Decreased from increased perfusion but not ventilation

Question 27

VQ greater than normal

Answer 27

Dead space ventilation
Anatomical dead space + wasted ventilation

Question 28

Henrys law

Answer 28

Solubility of a gas in a liquid increases as temperature decreases

Question 29

How much more soluble is CO2 than O2?

Answer 29

20

Question 30

How many breaths to remove alveolar air?

Answer 30

16 or more?

Question 31

What effects alveolar PO2?

Answer 31

Exercise, respiratory rate, oxygen pressure