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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0
Q

5 causes of hypoxemia

A

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

1
Q

Shunt

A

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

2
Q

hypoxemia

A

below normal PaO2 (low BLOOD O2)

3
Q

“hypoxic” means

A

low O2

4
Q

Hypoxic hypoxemia –> PaO2, PaCO2, PiO2?

A

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

5
Q

Tx for hypoxic hypoxemia

A

increase PiO2 (hyperventilate) to lower PaCO2

6
Q

Alveolar hypoventilation –> PaO2, PaCO2?

A

Low PaO2, High PaCO2

7
Q

Alveolar hypoventilation tx

A

Increase PiO2, increase Alveolar ventilation (open airway)

8
Q

Diffusion limitation –> PaO2, PaCO2?

A

Low PaO2, unchanged PaCO2 (still released normally)

9
Q

Diffusion limitation tx

A

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

10
Q

Shunt –> PaO2, PaCO2?

A

Low PaO2, slight increase in PaCO2

11
Q

Shunt tx

A

sx to fix shunt. INCREASING PiO2 HAS NO EFFECT

12
Q

VA/Q Mismatch –> PaO2, PaCO2?

A

low PaO2, High PaCO2

13
Q

Alveolar hypoventilation

A

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

14
Q

Diffusion limitation

A

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
Q

Low Pb (barometric pressure) –> PiO2

A

decreases

16
Q

What should VA/Q be normally?

A

1

17
Q

Normal PAO2

A

100mmHg

18
Q

Normal PACO2

A

40mmHg

19
Q

Normal PaCO2

A

40mmHg

20
Q

Normal PaO2

A

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

21
Q

Normal PvO2

A

40mmHg

22
Q

Normal PvCO2

A

45mmHg

23
Q

High perfusion with low ventilation –> V/Q?

A

Decreases

24
Q

Low perfusion with high ventilation –> V/Q?

A

Increases

25
Q

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

A

increases

26
Q

Asthma –> V/Q?

A

decreases

27
Q

why will oxygen therapy not help hypoxemia with shunts?

A

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
Q

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

A

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

29
Q

Reduced blood flow to alveoli –> PAO2, PACO2?

A

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
Q

Increased blood flow to alveoli –> PAO2, PaO2?

A

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
Q

Increased physiological dead space –> PO2, PCO2?

A

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

32
Q

respiratory quotient (R) =

A

oxygen metabolism = VCO2/VO2

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

33
Q

test for VA/Q shunt

A

discrepancy between O2 and CO2

34
Q

flow limited diffusion

A

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

35
Q

calculation of expected PAO2 with alveolar gas equation

A

PAO2 = PiO2 - [PACO2/R]

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