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pulm > SM_156a: Diffusion and Gas Transport > Flashcards

SM_156a: Diffusion and Gas Transport Flashcards

1
Q

The oxygen cascade is driven by a ________ gradient

A

The oxygen cascade is driven by a partial pressure gradient

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2
Q

What is Fick’s Law of diffusion?

A

V·= (A/t) * D * ∆P

where D is proportional to solubility / √molecular weight

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3
Q

The diffusion coefficient D for CO2 is ____ times that of O2

A

The diffusion coefficient D for CO2 is 20 times that of O2​

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4
Q

The diffusion path from alveolus to RBC includes the ______, _______, and _______

It is a ______ barrier to diffusion

A

The diffusion path from alveolus to RBC includes the alveolus, respiratory (alveolar-capillary) membrane, and capillary

It is a minimal barrier to diffusion

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5
Q

What are the two general categories of gas transfer between alveolus and capillary?

A
  • Diffusion limited
  • Perfusion limited
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6
Q

What is diffusion limited gas transfer between alveolus and capillary?

A

Gas transfer limited by rate of diffusion

Related to the Fick equation, V· = A/t * D * ∆P, which depends on the surface area available for diffusion and the diffusion distance

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7
Q

What is perfusion limited gas transfer between alveolus and capillary?

A

Gas transfer limited by the ability of the blood flow to deliver gas to the tissue

Related to rate of blood flow

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8
Q

What is diffusion limitation?

A

PA, g ≠ Pc’g where A is alveolar and c’ is end capillary

(example: rate of diffusion from alveolus to capillary is not sufficient to rase Pc‘O2 to PAO2 in a single pass through the lung)

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9
Q

What are the limiting factors to gas exchange described by Fick’s law of diffusion?

A
  • Surface area (pus, water, atelectasis)
  • Diffusion distance (emphysema, pulmonary fibrosis)
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10
Q

A patient briefly inhales 2 different gases, X and Y. Partial pressures of X and Y are then determined in alveoli, mixed venous blood, and end pulmonary capillary blood.

A

Y is diffusion limited, X is not

No equilibration between alveolus and capillary for Y, if increase surface area can increase diffusion rate

(X is perfusion limited)

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11
Q

For a gas (Y), that is diffusion limited, increasing cardiac output will __________

A

Decrease Pc’Y

Increasing cardiac output will decrease the amount of time blood spends in a pulmonary capillary, decreasing Pc’Y

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12
Q

What is perfusion limitation?

A

Rate of diffusion is sufficient so that end capillary partial pressure equals alveolar partial pressure (Pc’ = PA)

Example: nitrous oxide (PN20)

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13
Q

For a gas (Y), that is perfusion limited and with a constant PAY, a small increase in cardiac output will _______

A

For a gas (Y), that is perfusion limited and with a constant PAY, a small increase in cardiac output will have no effect on Pc’Y

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14
Q

Describe the diffusion of oxygen

A

Equilibration rate is between N2O and CO

Normally perfusion limited

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15
Q

What is the formula for diffusion capacity (DL)?

A

DL = V· / (PA - Pc)

1 / DL = resistance

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16
Q

What are the two components of resistance with regards to diffusing capacity?

A

1 / DL = 1 / Dm + 1 / (θ * Vc)

1 / Dm is resistance of alveolar-capillary membrane

1 / (θ * Vc) is resistance due to chemical reactions

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17
Q

What is the resistance due to chemical reactions for O2?

A

Binding of oxygen to hemoglobin

18
Q

What is the resistance due to chemical reactions for CO2​?

A

Conversion of bicarbonate to carbon dioxide

19
Q

Diffusion rate of CO2 ______ that of O2

A

Diffusion rate of CO2 is about equal to that of O2​

20
Q

Describe the diffusion of carbon dioxide

A

Chemical reactions slow equilibration

Perfusion limited

21
Q

How is oxygen transported through the blood?

A
  • Dissolved O2
  • Bound to hemoglobin (HbO2) - more common
22
Q

Which formula describes the transport of dissolved O2?

A

Henry’s Law, C(O2, dissolved) = K * PO2

23
Q

What is the formula for O2 delivery?

A

O2 delivery = O2 dissolved * cardiac output

24
Q

Describe the oxygen dissocation curve

A
  • Amount of O2 dissolved rises linearly w/ PO2 but is a small portion of total O2 (only dissolved O2 gives rise to partial pressure of oxygen)
  • HbO2 rises quickly
25
Q

What is the effect of hypoxia on HbO2 equilibrium?

A

Equilibrium: Hb + 4O2 ⇔ Hb(O2)4

At equilibrium:

  • Free [O2] on left = free [O2] on right
  • PO2 on left = PO2​ on right
  • Free [O2] on left < total [O2] on right

Hypoxia shifts the equilibrium

26
Q

What is the blood O2 capacity?

A

Amount of O2 bound to Hb when Hb is saturated

One gram Hb maximally binds 1.34 mL O2 and Hb is 15 gm% O2

O2 capacity is 1.34 mL/gm * 15 gm/100mL = 20.1 mL/dL

27
Q

What is oxygen content?

A

Amount of O2 carried by the blood, which varies with PO2

28
Q

What is the formula for % saturation?

A

%O2 saturation (SO2) = (O2 content / O2 capacity) * 100

29
Q

What is the HbO2 characterized by?

A
  • O2 binding capacity
  • P50, which is an expression of affinity of Hb for O2
30
Q

Altering [Hb] changes _______ but not ______ or _______

A

Altering [Hb] changes O2 capacity but not P50 or % saturation at any given PO2

31
Q

Which factors increase P50?

A

Curve shifted to the right by increases in

  • Temperature
  • H+ or PCO2 (Bohr effect)
  • 2,3-BPG
32
Q

What is the Bohr effect?

A

Deoxyhemoglobin is a weaker acid than oxyhemoglobin, so deoxyhemoglobin readily accepts H+, which lowers affinity of Hb for O2 in the tissue

33
Q

What is the Haldane effect?

A

Oxyhemoglobin is a stronger acid than deoxyhemoglobin, so oxyhemoglobin has a lower affinity for H+ and CO2, so addition of O2 causes H+ to be released from Hb in the lungs

34
Q

Where does the Bohr effect act?

A

In tissue

35
Q

Where does the Haldane effect act?

A

In lungs

36
Q

Compare O2 versus CO2 in the blood

A
  • CO2 curve is much more linear (never plateaus at physiological levels of CO2)
  • Much more CO2 than O2 in the blood
  • Hb is about 90% saturated w/ O2 at about 60 mmHg
37
Q

How is CO2 transported in the blood?

A
  • Dissolved CO2
  • HCO3- (mainly)
  • Carbamino CO2
38
Q

What is carbamino CO2?

A

CO2 bound to blood proteins (mostly hemoglobin)

39
Q

Higher O2 corresponds to the ______ line for carbamino CO2

A

Higher O2 corresponds to the arterial line for carbamino CO2​

40
Q

Lower O2 corresponds to the ______ line for carbamino CO2​

A

Lower O2 corresponds to the venous line for carbamino CO2​

pulm (32 decks)

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