L6 Gas diffusion across the repiratory membrane

Question 1

What are the requirements for constant gas transfer in the blood ?

Answer 1

1. Constant diffusion across respiratory membrane ( by maintaining a constant lung pressure )
2. Constant perfusion of blood in pulmonary circulation

Question 2

How the lung is maintaining his pressure constant ?

Answer 2

By not changing his volume a lot in one breath .. it takes 16 times to fully replace lung air with new air

Question 3

What are the components of respiratory unit/lobule ?

Answer 3

1. Respiratory bronchiole
2. Alveolar duct
3. Atria
4. Alveoli

Question 4

What are the components or respiratory membrane ?

Answer 4

1. This layer of fluid
2. Epithelium of the alveoli
3. Fused basement membrane
4. Endothelium of the capillaries

Question 5

What does the rate of diffusion of a gas depends on :

Answer 5

1. Gas solubility in the membrane
2. Gas solubility in the blood
3. Difference in partial pressures between alveoli and Blood (P1-P2)
4. Thickness of the membrane.(T)
5. Surface of the membrane (A)

Question 6

What is diffusion limited and what is perfusion limited ?

Answer 6

1. DIFFUSION LIMITED —> long equilibrium time
   - CO has low solubility in the membrane but very high in the blood and Hb … so it mainly depends on how much it will diffuse
2. PERFUSION LIMITED —

Question 7

Which gas transfer will be affected in the fibrosis ?

Answer 7

Oxygen mainly will be affected and will be changed from perfusion limited do diffusion limited

Question 8

What is the time for blood to be oxygenated in the capillaries ?

Answer 8

0.75 s however, normally at rest you need only 1/3 (0.25) and the rest is reserve

Question 9

What does the diffusion capacity depends on ?

Answer 9

1. Surface area
2. Thickness of membrane
3. Difference in the pressure
4. Perfusion
5. Hemoglobin in the blood

Question 10

Why the DLCO has a wide range ? When it increase and when it decrease ?

Answer 10

As CO binds very tightly to Hb and any increase or decrease in Hb amounts will affect the percentage of DLCO

Increase :

1. Pulmonary hemorrhage
2. Polycythemia
3. LHF
4. Left to right shunt

Decrease :

1. Anemia
2. Pulmonary artery obstruction

Question 11

What are the three main reasons which could lead to abnormal AaDO2?

Answer 11

1. Abnormal DLCO
2. Abnormal shunt ( anatomical or functional )
3. Ventilation / perfusion mismatch