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Respiratory 1 > Alveolar Gas Exchange > Flashcards

Alveolar Gas Exchange Flashcards

1
Q

Factors that determine the diffusion rate of gas across a barrier (alveoli) (4 total)

A
  1. Membrane Surface Area
  2. Membrane Thickness
  3. Pressure Gradient
  4. Solubility of Gas molecules
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2
Q

Law that explains the diffusion of a gas across the blood-gas barrier

A

Fick’s Law

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3
Q

(Oxygen vs. Carbon Dioxide) is relatively less soluble in water and tissue, and has much lower permeability across the blood:gas barrier

A

Oxygen

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4
Q

(Oxygen vs. Carbon Dioxide) is very soluble in water and tissue, and is so permeable across the blood:gas barrier that it is virtually always in equilibrium across the barrier

A

Carbon Dioxide

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5
Q

PAO2

A

Partial pressure of Oxygen in the alveoli

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6
Q

PaO2

A

Partial pressure of oxygen in the arteries/arterioles

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7
Q

Gradient for PO2 between the alveolar air and pulmonary capillary blood (mixed venous) is

A

64 mmHg

  • 104 mmHg (PAO2) - 40 mmHg (venous PO2) = 64
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8
Q

Gradient for PCO2 between the alveolar air and pulmonary capillary blood (mixed venous) is

A

6 mmHg

  • 46 mmHg (PACO2) - 40 mmHg (venous PCO2) = 6
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9
Q

Surface area of all of the alveoli in an adult human lung

A

70 sq. meters (large due to total of 300 million alveoli)

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10
Q

CO2 production on a typical mixed diet

A

200 mL/min

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11
Q

What tissues/cellular compartments does oxygen have to pass during gas exchange? (7)

A 
Alveolar Air
Surfactant
Alveolar Type 1 Cell
Lung Interstitium
Endothelial Cell
Blood Plasma
Red Blood Cell
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12
Q

Thickness of the blood-gas barrier

A

2 um

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13
Q

Why do PO2 and PCO2 equilibrate in almost the same amount of time across the blood:gas barrier if CO2 is much more permeable?

A

the oxygen gradient is about 10x higher than CO2

  • drives gas exchange despite its lower solubility
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14
Q

Why is it beneficial for oxygen and carbon dioxide to have equilibrated before the end of the pulmonary capillary (before the RBC leaves)?

A

there is reserve time for additional gas exchange (exercise or reduced O2 gradient at high altitudes)

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15
Q

PO2 is the pressure of oxygen bound to Hemoglobin (True or False)

A

False: when O2 is bound to Hb, it does not exert a partial pressure and is “taken out” of the partial pressure determination. The pressure sensed is “dissolved O2”.

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16
Q

Why is N2O (laughing gas) considered perfusion limited?

A

Gas exchange of N2O across blood-gas barrier is limited by blood flow through pulmonary capillaries (perfusion)

  • N2O is Highly permeable, does not bind to Hb, and equilibrates quickly
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17
Q

Why is CO considered diffusion limited?

A

Gas exchange of CO across blood-gas barrier is limited by diffusion process.

  • CO has a very low permeability; binds tightly to Hb; doesn’t equilibrate
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18
Q

When blood leaves the pulmonary capillary before it is equilibrated with a particular gas, the condition is termed…

A

Diffusion limited

  • Under normal conditions, CO behaves as diffusion limited.
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19
Q

When blood leaves the pulmonary capillary fully equilibrated with a particular gas, the condition is termed…

A

Perfusion limited

  • Under normal conditions, N2O, CO2, and O2 behave as perfusion limited.
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20
Q

How can pulmonary fibrosis affect the blood-gas barrier?

A

Thickened interstitium due to collagen deposition

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21
Q

How can pulmonary edema affect the blood-gas barrier?

A

Thickened interstitium due to excess fluid with or without alveolar flooding

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22
Q

Pulmonary fibrosis and edema can cause a _________ limited gas to become a _________ limited gas

A

Perfusion limited to diffusion limited

  • Can result in the O2-abnormal curve
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23
Q

Causes of Pulmonary edema

A
  1. Inc. permeability (damage via toxins, oxygen toxicity or RDS)
  2. Inc. Hydrostatic pressure (Pulmonary HTN, IV fluids, high central venous pressure)
  3. Dec. Osmotic pressure (Proteinuria, dilution by IV fluids)
  4. Dec. Lymphatic drainage (tumors)
24
Q

2/3 of the oxygen brought into the body is consumed by what organs in equal amounts?

A

Skeletal muscle
Brain
Liver

25
Q

What factors shift the oxygen-hemoglobin curve to the right, facilitating the release of O2 in metabolizing tissues?

A

low pH, high CO2, high temperature favor O2 unloading

26
Q

Why are the Oxyhemoglobin dissociation curves sigmoidal?

A

Due to the cooperativity between the four tetramers that form the Hb molecule as it binds four molecules of O2 in a stepwise fashion (one binds, makes it easier for others to bind) (one leaves, the rest want to leave as well)

27
Q

Normal arterial (PO2 vs. PCO2) is age dependent, decreasing with age

28
Q

Main “carrier” for CO2 in the blood

A

Plasma (bicarbonate)

29
Q

Main carrier for O2 in the blood

A

Hemoglobin

30
Q

the most convenient and common way to gain clinical information on oxygenation status; does not detect CO poisoning, but a lot easier than an arterial stick

A

Pulse oximetry

  • gives both pulse and Hb saturation
31
Q

Diffusion of a gas across the blood-gas barrier is directly proportional to

A
  1. SA
  2. pressure gradient
  3. permeability of the gas
32
Q

Diffusion of a gas across the blood-gas barrier is inversely proportional to the

33
Q

Which gradient is larger? PO2 or PCO2

A

PO2

  • Larger O2 pressure gradient helps drive gas exchange despite its lower solubility
34
Q

Estimated total number of alveoli in adult human lungs

A

300 million

35
Q

Estimated total number of capillaries in adult human lungs

A

280 billions

36
Q

About _____ second is required for O2 to react with Hb and this is relatively _____ amount of time.

A

0.2; large

37
Q

Why do starving kids have swollen belly?

A

Due to protein starvation which leads to a decrease in plasma oncotic pressure. Low plasma oncotic pressure opposes the retaining of fluid in the capillary circulation.

38
Q

What measures the diffusing capacity of the lung using CO?

A

DL-CO testing

39
Q

What factors can affect DL-CO?

A
  1. SA (decrease in SA by a disease will decrease diffusion)
  2. Permeability of CO (decrease in permeability will decrease diffusion)
  3. Hb status (anemia, smoker can affect the value)
  4. Body position, stress, exercise
40
Q

O2 is carried in the blood in what 2 forms?

A
  1. dissolved O2

2. bound to Hb

41
Q

At PaO2 = 100 mmHg, _____% of O2 is bound to Hb and _____% of O2 is dissolved O2.

42
Q

At PaO2 = 100 mmHg, Hb is ____% saturated

43
Q

What factors shift the oxygen-hemoglobin curve to the left, facilitating the binding of O2 in metabolizing tissues?

A

high pH, low CO2, cold temperature favor O2 loading

44
Q

Glycolysis product ______________ increases under hypoxic condition to decrease the affinity of Hb for O2 to facilitate oxygen release at tissue sites (where it is most needed).

45
Q

Oxygen-hemoglobin curve (arterial or venous blood) is more shifted to the right?

46
Q

CO2 is carried in plasma in what 3 forms?

A
  1. dissolved gas (10%)
  2. Bound to Hb as carbamino Hb (30%)
  3. MAINLY as HCO3- (bicarbonate) (60%)
47
Q

What enzyme carries out CO2 hydration reaction?

A

Carbonic Anhydrase (CA)

48
Q

Memorize CO2 hydration reaction

A

CO2 + H2O –> H2CO3 –> HCO3- + H+

49
Q

Unlike dissociation curve of oxygen, CO2-dissociation curve is

50
Q

What is the effect when oxygenation of Hb promotes the release of CO2?

A

the haldane effect

51
Q

B/C CO2-dissociation curve is linear, hypoventilation (halving ventilation) will cause alveolar PCO2 to

A

increase (double CO2 content)

52
Q

B/C CO2-dissociation curve is linear, hyperventilation (doubling ventilation) will cause alveolar PCO2 to

A

decrease (halving CO2 content)

53
Q

In Pulse Oximetry, Oxy Hb absorbs _______ and passes_______

A

infrared light; red light

54
Q

In Pulse Oximetry, Deoxy Hb absorbs _______ and passes_______

A

red light; infrared light

55
Q

Pulse oximetry is less accurate in

A

people with more darkly pigmented skin

Respiratory 1 (11 decks)

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