Physical Principles of Gas Exchange - Quiz 4

Question 1

In what directions do gas move?

Answer 1

Randomly, both in and out through membranes and fluids of respiratory structure

Question 2

What is the mechanism and rate of molecule transfer dependent on?

Answer 2

Gas Diffusion and Partial Pressure

Question 3

Basis of Gas Diffusion

Answer 3

• Gas molecules free to move across membranes
  
  • molecules not attached to one another
• Dissolve easily into fluids or tissues

Question 4

What is the energy source for gas diffusion?

Answer 4

Kinetic Motion

• Gas molecules move in a line at high velocity, bumping into eachother
• Random movement

Question 5

Net Diffusion of Gas

Answer 5

• When there is a concentration gradient, net diffusion of gas moves in one direction
• Rate of diffusion depends on pressure

Question 6

Composition of Air

Answer 6

• 79% N; 21% O₂
• 1 atm = 760 mmHg

Question 7

Henry’s Law

Answer 7

Solubility of gas in a liquid depends on

Temperature

Partial Pressure of gas over liquid

Nature of Solvent

Nature of Gas

Question 8

In water, ______ is 20x more soluble than ________

Answer 8

CO₂ is 20x more soluble than O₂

Question 9

What is the Rate of Net Diffusion determined by?

Answer 9

Difference of Partial Pressures (pp)

• pp in alveoli > blood = gas moves into blood (oxygen)
• pp in blood > alveoli - gas moves to alveoli (co₂)

Question 10

What is the Vapor Pressure when gas mixture is fully humidified to 37 C?

Answer 10

47 mmHg

• VP depends on temp. Higher temp = higher kinetic energy and more water escaping into gas

Question 11

Partial Pressure of Oyxgen in Upper Airway

Answer 11

713 mmHg * 21% = 150 mmHg

Question 12

Factors that Affect Gas Diffusion Rates

Answer 12

Pressure Differences

Gas Solubility in Fluid

Area of Fluid

Distance for gas diffusion

Molecular Weight of Gas

Temperature of Fluid (constant in body)

Question 13

D is __________ proportional with solubility and __________ proportional to the sq. root of the gas’ molecular weight.

Answer 13

Directly, Inversely

Question 14

What are respiratory gases highly soluble in?

Answer 14

Lipids

Question 15

What limits the rate of gas movement into tissues?

Answer 15

Diffusion rate of gas through tissue water

Movement of gas into/out of tissues = diffusion rate of gas through water

Question 16

Why is Alveolar air different from Atmospheric Air?

Answer 16

• Alveolar air is partially replaced by atm. air with each breath.
• O₂ constantly going to blood and CO₂ to alveoli
• Air entering lung is humidified, diluting gas partial pressures

Question 17

What concept prevents sudden changes in gas concentrations and allows respiratory stability?

Answer 17

The way alveolar air is renewed - multiple breaths needed to exchange alveolar air.

• 350 ml of air/breath
• FRC = 2500 mL
• Each breath replaces a seventh of FRC
• prevents sudden changes in gas concentrations
• allows more respiratory control

Question 18

How long does it take for normal breathing to remove 1/2 of alveolar gas

Answer 18

17 Seconds

Question 19

What is normal alveolar PO₂

Answer 19

100 mmHg

Question 20

What is normal alveolar PCO₂?

Answer 20

40 mmHg

Alveolar PCO₂ increases in proportion to CO₂ excretion

Question 21

When is Dead Space Air and Alveolar Air expired?

Answer 21

Dead Space Air expired in first portion and alveolar air is expired at end of exhalation

Question 22

Factors that affect rate of gas diffusion through respiratory membrane

Answer 22

Thickness of Resp. Membrane

Surface area of Resp. Membrane

Coefficient (D)

Pressure Difference across Resp. Membrane

Question 23

Rate of diffusion is ______ proportional to membrane thickness

Answer 23

Inversely

Increase in thickness by 2-3x significantly interferes

EX: Edema, Fibrosis

Question 24

How does decreasing membrane surface area effect Diffusion Rate?

Answer 24

Decreasing surface area by 1/4 impedes gas significantly

EX: Removing Lung tissue or Emphysema (5x decrease)

Question 25

How much faster does CO₂ diffusion in relation to O₂

Answer 25

CO₂ diffuses 20x faster than O₂

Question 26

How much faster does O₂ diffuse in relation to Nitrogen

Answer 26

O₂ diffuses twice as fast as Nitrogen

Question 27

What is Diffusion Capacity

Answer 27

Volume of gas that will diffuse through the resp. membrane each minute for a pressure difference of 1 mmHg

Question 28

In what terms is the ability to exchange gas b/t alveoli and pulmonary blood expressed?

Answer 28

In Quantitative Terms

Question 29

Factors that affect diffusion rate through resp. membrane also affect what?

Answer 29

Diffusion Capacity

Question 30

What is the diffusion capacity for O₂

Answer 30

21 mL/min/mmHg

Question 31

What is the mean oxygen pressure difference across the resp. membrane

Answer 31

11 mmHg

Question 32

How is the Total Quantity of O₂ diffusing across membrane per minute calculated?

Answer 32

Total amt. of O₂ diffusing = Pressure Difference X Diffusing Capacity

Question 33

How is Diffusing Capacity effected by Exercise?

Answer 33

Increases 3-5x to Max (65 mm/min/mmHg)

d/t more recruitment and better V/Q

Question 34

Resting Diffusing Capacity of CO₂

Answer 34

400 mL/min/mmHg

Question 35

Diffusing Capacity of CO2 with Exercise

Answer 35

1200 mL/min/mmHg

Question 36

Carbon Monoxide Method for Measuring Diffusing Capacity

Answer 36

Used to calculate O2 Diffusion Capacity

1. Measure alveolar CO pressure
2. Multiply CO diffusing capacity by 1.23

Question 37

What is the quantity of V/Q if there is perfusion, but no ventilation

Answer 37

V/Q = 0

Question 38

What is the quantity of V/Q when there is ventilation, but no perfusion?

Answer 38

V/Q = Infinity

Question 39

What is the PO₂ and PCO₂ in normal deoxygenated Blood?

Answer 39

PO₂ = 40 mmHg

PCO₂ = 45 mmHg

Question 40

When is V/Q Below Normal

Answer 40

Shunt: Perfusion, no Ventilation

Question 41

When is V/Q greater than Normal?

Answer 41

Dead Space: Ventilaton, no Perfusion

Question 42

Diffusing Capacity of CO

Answer 42

17 mm/min/mmHg