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Pulmonary Week 1 > Gas Exchange > Flashcards

Gas Exchange Flashcards

1
Q

What is the fraction of O2 in air? Nitrogen? Co2?

A

21% O2
78% nitrogen
0.3% CO2

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2
Q

What is the eqn for minute ventilation?

A

Tidal volume*(Respiration rate)

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3
Q

T or F. All inspired air reaches the alveoli

A

F. There are anatomic (and functional) dead spaces

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4
Q

What is alveolar dead space?

A

alveoli that are ventilated but NOT perfused with blood so they cannot participate in gas exchange

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5
Q

What is the physiologic dead space?

A

the anatomic dead space + alveolar dead space

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6
Q

What is the eqn for alveolar ventilation (aka effective ventilation)?

A

minute ventilaton - dead space

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7
Q

Physiologic dead space represents what fraction of tidal volume?

A

25-30%

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8
Q

T or F. Dead space is static

A

F. Dead space increases with lung volume (deep inspiration)

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9
Q

Does dead space increase or decrease in exercise?

A

decrease because the increase in tidal volume is overshadowed by a huge increase in perfusion recruitment

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10
Q

Can increased alveolar dead space ever be a good thing?

A

No, always pathologic (e.g. pulmonary embolism)

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11
Q

R= Respiratory Exchange Ratio.

A

= Vco2 (co2 production)/ Vo2 (O2 consumption)

normal = 200/250= 0.8

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12
Q

What is the eqn for alveolar gas exchange?

A

PAO2= PiO2- (PaCO2/R)

where R = Vco2 (co2 production)/ Vo2 (O2 consumption)

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13
Q

What does hyperventilation do to PacO2?

A

decreases it (you are pushing it off).. so PAO2 increases

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14
Q

How can you calculate arterial oxygen tension (PaO2)?

A

measure directly with arterial blood gas test

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15
Q

How can you calculate alveolar oxygen tension (PAO2)?

A

alveolar gas eqn

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16
Q

What does a widened A-a difference suggest? What is normal?

A

intrinsic lung disease

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17
Q

Eqn for PiO2?

A

(Pb-Ph20)*FiO2

18
Q

T or F. A-a gradient increases with age

A

T. We cant diffuse gas as well

19
Q

What is the formula for a normal A-a gradient?

A

(Age+4)/4

20
Q

What is hypoxemia?

A

decreased PaO2 in blood

21
Q

Hypoxemia with a normal A-a difference suggests what?

A

No lung disease, so either decreased PiO2 or hypoventilation

22
Q

Hypoxemia with a widened A-a difference suggests what?

A

LUNG DISEASE, so either:

  • diffusion limitation
  • R-to-L shunt
  • Ventilation/perfusion (V/Q) mismatch
23
Q

When can decreased PiO2 occur?

A

-altitude

24
Q

Rule of thumb for A-a gradient

A

an increase in A-a gradient of 10% isn’t that indicative of lung disease.. play it case by case

25
Q

Why would a diffusion limitation become evident when walking/exercising?

A

Because normally RBCs take up to 0.75s to transmit a pulmonary capillary while full o2 binding only requires 0.25s but during exercise CO increases and blood moves faster so PaO2 decreases

26
Q

T or F. 100% FiO2 infusion ELIMINATES effects of diffusion limitations

A

T. Normalizes A-a ratio and PaO2

27
Q

What is a shunt?

A

a fraction of venous blood bypasses alveoli and enters systemic circulation de-oxygenated

28
Q

What is a normal physiologic shunt?

A

5%

29
Q

T or F. 100% FiO2 infusion ELIMINATES effects of shunts

A

F. Only cause that doesn’t correct with 100% O2

30
Q

What is the overall V/Q of the lung?

A

0.8

31
Q

T or F. 100% FiO2 infusion ELIMINATES effects of V/Q mismatch

A

T.

32
Q

What are some causes of low V/Q?

A
  • obstructive disease (COPD, asthma)
  • shunt (V/Q=0)**
  • pulmonary edema
33
Q

What are some causes of high V/Q?

A
  • pulmonary embolism

- extreme high is DEAD SPACE

34
Q

T or F. Most lung disease cause V/Q mismatch

A

T. V/Q Mismatch is the most common cause of hypoxemia

35
Q

What is a normal PaO2?

A

100- age*0.3

36
Q

Is FEV1:FVC decreased in asthma?

A

Yes

37
Q

How can you differentiate between COPD and asthma with PFTs?

A

both low FEV1:FVC but only EMPHYSEMA has a low DLCO, normal in asthma and chronic bronchitis

38
Q

How does PAH/PE present on PFT?

A

NORMAL PFT but low DLCO

39
Q

How can you differentiate between interstitial disease and chest wall disease with PFTs?

A

both have normal FEV1:FVC interstitial disease has a low DLCO and chest wall disease is normal

40
Q

What are some things that cause low DLCO?

A
  • anemia
  • interstitial lung disease
  • emphysema
  • pulmonary vascular disease (PAH, pulmonary emboli)
41
Q

What things can produce high DLCO (120+%)?

A
  • Early CHF
  • Obesity
  • Pulmonary Alveolar hemorrhage
42
Q

Eqn for arterial oxygen content of blood

A

= 1.39HbO2sat% + 0.003*PaO2

Pulmonary Week 1 (17 decks)

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