Diffusion and Perfusion

Question 1

True or False: Oxygen is poorly soluble in blood

Answer 1

True: this is why it binds to hemoglobin and most o2 binding sites on Hb are saturated

Question 2

What portion of arterial oxygen does PaO2 relate to?

Answer 2

This only represents the partial pressure of freely dissolved oxygen, not oxygen that is bound to hemoglobin

Question 3

What is the relationship between hemoglobin O2 and PaO2?

Answer 3

indirectly proportional through oxygen dissociation curve

Question 4

How does hemoglobin affect Ficks law? (FLUX = Change P x (A/d) x K)

Answer 4

hemoglobin binding to oxygen keeps the change P high so that there is a gradient for diffusion

Question 5

What is a normal value for Pv02?

Answer 5

40 torr

Question 6

How much of the lung space capillaries does venous blood need to pass through to return arterial oxygen to 100 torr?

Answer 6

1/3 of the lung space is required to return venous blood to arterial blood oxygen levels. Decreases in this curve (more lung space required) are caused by exercise and moderate disease

Question 7

Why is it good that only 1/3 of the lung is required to return venous oxygen levels to arterial oxygen levels?

Answer 7

because if you are exercising or have moderate lung disease, you have extra lung space to compensate and return to normal

Question 8

What does interstitial dz do to cause diffusion disease?

Answer 8

there is an increase in diffusion distance

Question 9

What does emphysema do to cause diffusion disorder?

Answer 9

there is decreased area for oxygen exchange

Question 10

Why does severe disease not normally effect the diffusion of CO2?

Answer 10

because the solubility of CO2 in the blood is high so it diffuses readily

Question 11

Why is oxygen diffusion affected by disease?

Answer 11

because oxygen must be unbound from hemoglobin and dissolve into the blood before it can diffuse

Question 12

What are 4 factors that affect perfusion?

Answer 12

• O2 tension
• Hypoxic pulmonary vasoconstriction
  - when low O2 is present, vasoconstriction occurs
• Capillary recruitment
  - in exercise, vessels open due to increased CO
• Gravity
  - blood pools at base of lung so increased Q at base

Question 13

What is an ideal V/Q?

Answer 13

1

Question 14

Why does a high V/Q result in marginal increase in O2 concentration in blood?

Answer 14

Because oxygen saturation of hemoglobin limits how much oxygen high V/Q branch can add

Question 15

What happens to PaO2 with low V/Q (V/Q mismatch)? PaCO2?

Answer 15

PaO2 will decrease

PaCO2 will remain unchanged

Question 16

What results with the highest V/Q possible?

Answer 16

dead space

Question 17

what results with the lowest V/Q possible?

Answer 17

shunt

Question 18

what is a shunt?

Answer 18

volume of blood that does not engage in gas exchange

Question 19

V/Q mismatch due to gravity results in how much torr difference between PAO2 and PaO2?

Answer 19

5-10 torr