Respiration Lecture 10: Ventilation-Perfusion Relationships Flashcards Preview

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Flashcards in Respiration Lecture 10: Ventilation-Perfusion Relationships Deck (36):
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Shunt

flow of blood from R to L heart bypassing the gas exchange area

1

5 causes of hypoxemia

1)Hypoxic hypoxemia
2)alveolar hypoventilation
3) diffusion limitation
4)shunt
[5)VA/Q mismatch]

2

hypoxemia

below normal PaO2 (low BLOOD O2)

3

"hypoxic" means

low O2

4

Hypoxic hypoxemia --> PaO2, PaCO2, PiO2?

Low PaO2, LOW PaCO2, low PiO2. Low PaCO2 because of low PiO2

5

Tx for hypoxic hypoxemia

increase PiO2 (hyperventilate) to lower PaCO2

6

Alveolar hypoventilation --> PaO2, PaCO2?

Low PaO2, High PaCO2

7

Alveolar hypoventilation tx

Increase PiO2, increase Alveolar ventilation (open airway)

8

Diffusion limitation --> PaO2, PaCO2?

Low PaO2, unchanged PaCO2 (still released normally)

9

Diffusion limitation tx

Increase PiO2 to increase conc. gradient for O2 to flow in

10

Shunt --> PaO2, PaCO2?

Low PaO2, slight increase in PaCO2

11

Shunt tx

sx to fix shunt. INCREASING PiO2 HAS NO EFFECT

12

VA/Q Mismatch --> PaO2, PaCO2?

low PaO2, High PaCO2

13

Alveolar hypoventilation

decreased ventilation that doesn't provide sufficient refreshening of the alveolar gas to maintain PACO2

14

Diffusion limitation

increasing the difficulty for O2 to diffuse from alveoli to blood by thickening the diffusion barrier such as pulmonary edema. Rarely causes clinical hypoxemia

15

Low Pb (barometric pressure) --> PiO2

decreases

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What should VA/Q be normally?

1

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Normal PAO2

100mmHg

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Normal PACO2

40mmHg

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Normal PaCO2

40mmHg

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Normal PaO2

functionally 100mmHg (actually 95mmHg in a normal shunt)

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Normal PvO2

40mmHg

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Normal PvCO2

45mmHg

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High perfusion with low ventilation --> V/Q?

Decreases

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Low perfusion with high ventilation --> V/Q?

Increases

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Restriction of blood flow to alveolar space --> physiological dead space

increases

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Asthma --> V/Q?

decreases

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why will oxygen therapy not help hypoxemia with shunts?

Hb is already saturated on functional side, and oxygen can't get to non-functional side to saturate the Hb, so at most there is a slight improvement in Hb saturation with oxygen therapy

28

Why will increased PiO2 help when airway is restricted but not blocked off?

Some O2 can still get down to alveoli and participate in gas exchange, which will raise PO2

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Reduced blood flow to alveoli --> PAO2, PACO2?

Increased PAO2 because there isn't enough blood going by to draw out the O2 from the alveoli. Decreased PACO2 because less blood is flowing by to drop off its CO2

30

Increased blood flow to alveoli --> PAO2, PaO2?

PAO2 is normal, PaO2 is decreased because there is too much blood flowing by to oxygenate all of it and same amount of O2 is pulled from the alveoli

31

Increased physiological dead space --> PO2, PCO2?

High ventilation, low perfusion. PO2 increases because there is more O2 coming into alveoli than leaving. PCO2 drops because low perfusion allows less CO2 to be deposited back in alveoli

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respiratory quotient (R) =

oxygen metabolism = VCO2/VO2

A fx of diet: carbs are most efficient, proteins least efficient. fat moderately efficient

33

test for VA/Q shunt

discrepancy between O2 and CO2

34

flow limited diffusion

when flow rate becomes high enough to pass blood through the gas exchange are before equilibrium is reached, resulting in lower PaO2

35

calculation of expected PAO2 with alveolar gas equation

PAO2 = PiO2 - [PACO2/R]

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