Alveolar Gas Exchange I

Question 1

In referring the the exchange of gases between alveolar air and blood, what is the total time for transfer referring to?

Answer 1

sum of diffusion time and chemical reaction time

Question 2

How long is the total time for transfer for blood passing through the pulmonary capillary?

Answer 2

0.75 s

Question 3

What is the driving force behind rate of diffusion in referring to the alveolar-capillary diffusion?

Answer 3

Partial pressure difference (∆P) between alveoli and pulmonary capillary blood for each gas (not concentration difference)

Question 4

What factors determine rate of diffusion?

Answer 4

1. Ease of diffusion
2. Driving force

Question 5

What factors determine ease of diffusion?

Answer 5

1. Surface area
2. Diffusion Distance (ΔX)
3. Diffusion coefficient (D)

Question 6

What does surface area of alveolar capillary diffusion refer to?

Answer 6

the alveolar area available for diffusion

Question 7

What type of diseases will surface area available for diffusion decrease? When will it increase

Answer 7

• degenerative lung diseases and pulmonary embolism
• Increases in deep inspiration (i.e exercise)

Question 8

What does diffusion distance refer to when talking about alveolar-capillary diffusion?

Answer 8

the alveolar-capillary membrane has several compartments but all are normally thin (even interstitial space)

Question 9

What conditions are able to increase diffusion distance?

Answer 9

pulmonary edema and pneumonia

Question 10

What does the diffusion coefficient mean?

Answer 10

depends on molecular weight of the gas** (not normally a major factor) and its **water solubility (major factor).

Question 11

Which has a higher diffusion coefficient? Oxygen or CO₂?

Answer 11

CO2

Question 12

What is possible in cases of decreased diffusion rate?

Answer 12

hypoxia may occur much faster than hypercapnia

Question 13

What is Fick’s Law Equation?

Answer 13

Question 14

What is the diffusing capacity for lungs equation?

Answer 14

Units in (ml/(min*mmHg)

Question 15

How do you calculate flow of gas across a barrier?

Answer 15

The flow of gas across a barrier (Vx) is proportional to its diffusing capacity(DL) and to its partial pressure gradient across the barrier

Question 16

What is the DO2 at rest? At exercise?

Answer 16

Do₂ = 21 ml/min/mmHg at rest, 30-60 ml/min/mmHg in exercise (probably due to an increase in diffusion area as pulmonary capillaries open)

Question 17

What is the D_CO2 at rest?

Answer 17

Dco₂ = 450 ml/min/mmHg (at rest)

Question 18

What is the D_CO?

Answer 18

Dco = Do₂ / 1.23 or Do₂ = 1.23 x Dco

Question 19

D_CO is a good measurement for what?

Answer 19

estimating diffusion capacity of the lungs

Question 20

What is the driving force (O2 P gradient) for pulmonary exchange of oxygen?

Answer 20

PA-o₂ - Pv-o₂ = 100 mmHg – 40 mmHg = 60 mmHg

Question 21

For normal Do₂ O₂ requires how much time to reach equilibrium?

Answer 21

0.25 s

Question 22

What is capillary reserve time?

Answer 22

- the portion of the erythrocyte transit time in which no further diffusion of oxygen occurs: 0.75 – 0.25 = 0.5 sec.

Question 23

PO2 in normal arterial blood is lower or higher than alveolar air?

Answer 23

lower (non equilibration) 97

Question 24

How does Hyperventilation and Hypoventilation affect P_AO₂, P_aO₂ and A-a gradient?

Answer 24

Hyperventilation: ↑ P_AO₂ and P_aO_2, N A-a gradient.

Hypoventilation: ↓ P_AO₂ and P_aO₂, N A-a gradient

Question 25

Driving force of P_CO2 in pulmonary exchange of CO_2.

Answer 25

PA-co₂ - Pv-co₂ = 46 mmHg – 40 mmHg = 6 mmHg

Question 26

How does high Dco2 effect alveolar and pulmonary capillary blood gas exchange?

Answer 26

High Dco2 almost always permits complete equilibration of CO2 between alveolar gas and pulmonary capillary blood

Question 27

What are the limitations of pulmonary diffusion of gases? (Give examples)

Answer 27

Transfer of gases is limited by the availability of the gas for diffusion and diffusion rate – end capillary gas tension is less than alveolar gas partial pressure

- CO

- O2 in strenuous exercise and abnormalities of respiratory membrane (emphysema, fibrosis)

- CO2 in severe alveolo-capillary abnormality

Question 28

T/F The amount of gas entering the body is limited by the blood flow in the pulmonary capillaries (perfusion) as the blood equilibrates with alveolar gas early in its passage through the capillary

Answer 28

True

Question 29

PO2 in normal arterial blood is lower or higher than in alveolar air?

Answer 29

lower (97 mmHg) non equilibration

Question 30

Which of the following statements most accurately describes the graphs on the right?

a. for the line labeled “normal”, O2 is a perfusion limited gas with normal arterial hemoglobin saturation
b. for the line labeled “normal”, O2 is a diffusion limited gastric with normal arterial hemoglobin saturation
c. for the line labeled “fibrosis” O2 is a perfusion limited gas with below-normal arterial hemoglobin saturation
d. for the line labeled “fibrosis”, O2 is a diffusion limited gas with below-normal arterial hemoglobin saturation
e. for both lines, O2 is a diffusion limited gas with below-normal arterial hemoglobin saturation

Answer 30

d. For the line labeled “fibrosis”, O2 is a diffusion limited gas with below-normal arterial hemoglobin saturation

Question 31

Answer the following question related to the graph.

Answer 31

D. Venous admixture