Respiration Lecture 10: Ventilation-Perfusion Relationships

Question 0

5 causes of hypoxemia

Answer 0

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

Question 1

Shunt

Answer 1

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

Question 2

hypoxemia

Answer 2

below normal PaO2 (low BLOOD O2)

Question 3

“hypoxic” means

Answer 3

low O2

Question 4

Hypoxic hypoxemia –> PaO2, PaCO2, PiO2?

Answer 4

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

Question 5

Tx for hypoxic hypoxemia

Answer 5

increase PiO2 (hyperventilate) to lower PaCO2

Question 6

Alveolar hypoventilation –> PaO2, PaCO2?

Answer 6

Low PaO2, High PaCO2

Question 7

Alveolar hypoventilation tx

Answer 7

Increase PiO2, increase Alveolar ventilation (open airway)

Question 8

Diffusion limitation –> PaO2, PaCO2?

Answer 8

Low PaO2, unchanged PaCO2 (still released normally)

Question 9

Diffusion limitation tx

Answer 9

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

Question 10

Shunt –> PaO2, PaCO2?

Answer 10

Low PaO2, slight increase in PaCO2

Question 11

Shunt tx

Answer 11

sx to fix shunt. INCREASING PiO2 HAS NO EFFECT

Question 12

VA/Q Mismatch –> PaO2, PaCO2?

Answer 12

low PaO2, High PaCO2

Question 13

Alveolar hypoventilation

Answer 13

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

Question 14

Diffusion limitation

Answer 14

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

Question 15

Low Pb (barometric pressure) –> PiO2

Answer 15

decreases

Question 16

What should VA/Q be normally?

Answer 16

1

Question 17

Normal PAO2

Answer 17

100mmHg

Question 18

Normal PACO2

Answer 18

40mmHg

Question 19

Normal PaCO2

Answer 19

40mmHg

Question 20

Normal PaO2

Answer 20

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

Question 21

Normal PvO2

Answer 21

40mmHg

Question 22

Normal PvCO2

Answer 22

45mmHg

Question 23

High perfusion with low ventilation –> V/Q?

Answer 23

Decreases

Question 24

Low perfusion with high ventilation –> V/Q?

Answer 24

Increases

Question 25

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

Answer 25

increases

Question 26

Asthma –> V/Q?

Answer 26

decreases

Question 27

why will oxygen therapy not help hypoxemia with shunts?

Answer 27

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

Question 28

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

Answer 28

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

Question 29

Reduced blood flow to alveoli –> PAO2, PACO2?

Answer 29

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

Question 30

Increased blood flow to alveoli –> PAO2, PaO2?

Answer 30

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

Question 31

Increased physiological dead space –> PO2, PCO2?

Answer 31

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

Question 32

respiratory quotient (R) =

Answer 32

oxygen metabolism = VCO2/VO2

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

Question 33

test for VA/Q shunt

Answer 33

discrepancy between O2 and CO2

Question 34

flow limited diffusion

Answer 34

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

Question 35

calculation of expected PAO2 with alveolar gas equation

Answer 35

PAO2 = PiO2 - [PACO2/R]