Trachte: Diffusion

Question 1

What is diffusion? What happens to CO2? O2?

Answer 1

Process by which O2 moves from higher to lower pressure

CO2 goes form blood to alveoli
O2 goes from blood to alveoli

Question 2

What is diffusion proportional to? Inversely proportional to?

Answer 2

SA

Barrier thickness

Question 3

What is surface area?

Answer 3

50-100 m2

Question 4

What reduces SA?

Answer 4

COPD

atelectasis- Collapse of alveoli

Question 5

What is thickness of the alveoli?

Answer 5

Less than 1 um

Question 6

What would increase the thickness?

Answer 6

Water layer
fibrosis
Biofilm from bacteria

Question 7

What is the driving force of diffusion?

Answer 7

Concentration differences (partial pressure differences)

Question 8

How do molecular weight and solubility affect diffusion?

Answer 8

Molecular weight- bigger things don’t diffuse well

solubility- more soluble things diffuse better

Question 9

How does CO2 diffusion differ from O2 diffusion?

Answer 9

CO2 diffusion is 20x better

Question 10

How does CO react with the blood? What type of gas is it?

Answer 10

RBC affinity is SO great that CO equilibrate w/ the RBC immediately so there is NO increase in PP

DIFFUSION LIMITED gas (the blood alveolar membrane is the only constraint on gas transfer)

Question 11

When can oxygen transfer by diffusion be limited?

Answer 11

Pulmonary diseases–> increased thickening of blood-gas barrier

Pneumonia
Decreased PP of O2 (high altitude)

Question 12

What are the three diffusion limited processes?

Answer 12

1. Reaction of CO with blood
2. Limited in pulmonary diseases
3. Different solubilities in blood and the blood gas barrier

Question 13

What are perfusion limited processes?

Answer 13

1. Reaction of N20 w/ blood
2. Oxygen reaction w/ blood
3. Gases w/ similar solubilities in blood and the blood gas barrier
4. CO2 is a gas that is not typically diffusion limited

Question 14

Does N20 react w/ RBC?

What happens to PP of N20 as it passes through capillaries? When is it saturated?

Answer 14

Does NOT react w/ RBC

Builds as blood goes through capillaries–saturated 10% of way through the capillary

Question 15

What limits N2O saturation?

Answer 15

Blood flow NOT the alveolar barrier

Question 16

Why is CO2 NOT diffusion limited?

Answer 16

crosses the alveolar wall easily

VERY soluble

Question 17

What is venous O2 pressure normally? What is alveolar O2 pressure? What does this cause? How long does it normally take to reach saturation?

Answer 17

40 mmHg

100 mmHg

O2 to move from alveoli to capillary

.25 sec

Question 18

How long does it take for O2 to totally traverse the pulmonary capillary?

Answer 18

.75 sec

Question 19

What might happen to the traverse during exercise? What happens if you have COPD or HF?

Answer 19

Reduced by .25 sec

still reaches EQUILIBRIUM in the capillary BUT if the diffusion barrier is INCREASED it may NOT reach equilibrium–> blood PO2 less than 100 mmHg

Question 20

What is the easiest example of diffusion limitation?

Answer 20

Breathing low PO2 (high altitude)

Question 21

What is the driving force of diffusion if alveolar PO2 is 60 mmHg?

Answer 21

20–> less diffusion

Question 22

How do you measure diffusing capacity?

Answer 22

Use CO b/c it’s NOT Perfusion limited

Question 23

What is the formula for diffusion capacity?

Answer 23

DC = Vco/ (P1-P2)

Question 24

What is normal DC??

Answer 24

25 ml/min/mmHg

Question 25

What happens to diffusion capacity during exercise?

Answer 25

INCREASES (recruitment and distension of pulmonary capillaries)

Question 26

How long does it take for O2 to combine w/ RBC?

Answer 26

.2 sec

Question 27

What is the formula for resistance of hte blood gas barrier?

Answer 27

Resistance = (P1-P2) / V

P=FXR

Question 28

What are diffusion limited gases?

Answer 28

CO and O2

Question 29

What are perfusion limited gases?

Answer 29

N2O, O2 and CO2