Diffusion (Trachte) - W1

Question 1

What 5 things determine diffusion across the blood-gas barrier?

Answer 1

• Pressure difference (driving force)
• Surface area
• thickness
• molecular weight
• solubility of gas in barrier

Question 2

What gradient does diffusion follow?

Answer 2

• goes from high to lower pressure
  
  • concentration has NO EFFECT.
• oxygen goes from alveoli to blood
  
  • 100mmHg in alveoli
• CO2 goes from blood to alveoli
  
  • 45mmHg in blood to 0 in alveoli

Question 3

How does surface area affect the barrier?

Answer 3

more surface area = more diffusion.

If lungs are not inflated all the way the surface area is reduced.

Question 4

How does thickness affect the barrier?

Answer 4

• very small thickness = more diffusion

pulmonary edema could increase the thickness of the barrier leading to less diffusion.

Question 5

how does molecular weight affect diffusion?

Answer 5

LOWER molecular weight = better diffusion.

Question 6

How does solubility of gas affect diffusion?

Answer 6

• more soluble things diffuse better
• CO2 diffuses 20x better than O2
• with hypoxia, see normal CO2 levels but low oxygen since CO2 doesn’t diffuse across the barrier as well

Question 7

What are gases that are perfusion limited?

Answer 7

• Nitrogen - saturated 10% through blood flow
• oxygen - equilibrated 1/3 of the way through the capillaries
• CO2 - not typically perfusion limited. Crosses alveolar well relatively easily.

Question 8

What increases a perfusion limited process?

Answer 8

BLOOD FLOW!

with more blood flow, oxygen has more blood to diffuse into.

Question 9

What is the definition of a perfusion limited process?

Answer 9

EQUALLY soluble in blood and the barrier

Question 10

What are examples of diffusion limited processes?

Answer 10

• Reaction of carbon monoxide with blood.
• oxygen - in disease states.

Question 11

What is the definition of a diffusion limited process?

Answer 11

• UNEQUAL solubility in blood and the blood-gas barrier
• has to be MORE solube in the blood

Question 12

Why is CO diffusion limited?

Answer 12

reacts w/hemoglobin as soon as it crosses the membrane. No bulidup of partial pressure in plasma so only thing limiting it is diffusion.

Question 13

What could cause an increased barrier to diffusion, which makes oxygen diffusion limited?

Answer 13

• higher altitdues w/low PO2
• pulmonary diseases

Question 14

Explain oxygen uptake into the pulmonary capillaries:

Answer 14

• alveolar PO2 = 100, capillary is 40 - leaves gradient of 60.
• If barrier is thickened, it might not reach equilibirium. Blood PO2 would be less than 100, so there would be a smaller gradient.
  
  • higher altitudes make diffusion worse.

Question 15

How do we measure diffusion capacity?

Answer 15

• use carbon monoxide since IT’S NOT PERFUSION LIMITED.
• =volume of CO transferred/partial pressure difference. – Vco/(P1-P2)
• pressure gradient normally fixed at 2.2 and time is 10 sec (.16 minutes). Value that changes is V - how much you breath in and out.
• V will increaes with exercise.

Question 16

What is the resistance of the blood-gas barrier?

Answer 16

• (P1-P2)/V
• Everhting relies on P= FxR
• need pressure difference for oxygen to acutally flow
• opposite of diffusing capacity.