Phys - Ventilation/Perfusion Relationships

Question 1

How does pulmonary vascular resistance compare to systemic vascular resistance?

Answer 1

Lower

Question 2

Pulmonary artery pressure v. aortic pressure

Answer 2

14 mmHg v. 100 mmHg

Question 3

Right ventricular output =

Answer 3

Left ventricular output = CO

Question 4

Amount of blood entering pulmonary artery in 1 min

Answer 4

5 L
(= CO since LV output = RV output)

Question 5

So pressure and resistance are both lower in the pulmonary vasculature compared to systemic vasculature but the flow is the same. How is this possible?

Answer 5

Q=P/R; pressure and resistance in pulmonary vasculature decrease proportionally, so the ratio, hence the flow, is the same in both vascular beds

Question 6

PBF =

Answer 6

(P_pulm artery - P_LV)/R

Question 7

High/low at apex:
Palv
Pa
Q
R

Answer 7

Palv- high
Pa- low
Q- low
R- high

Question 8

High/low at base:
Palv
Pa
Q
R

Answer 8

Palv- low
Pa- high
Q- high
R- low

Question 9

Which zone?

Pa>PA>Pv

Answer 9

Zone 2

Question 10

Which zone?

PA>Pa>Pv

Answer 10

Zone 1

Question 11

Which zone?

Pa>Pv>PA

Answer 11

Zone 3

Question 12

Besides blood flow, why is keeping pulmonary arterial pressure low important?

Answer 12

Keeps lungs dry

Question 13

Promote fluid movement into or out of capillary: interstitial fluid pressure

Answer 13

Out

Question 14

Promote fluid movement into or out of capillary: oncotic pressure of plasma proteins

Answer 14

In

Question 15

Promote fluid movement into or out of capillary: Capillary hydrostatic pressure

Answer 15

Out

Question 16

Promote fluid movement into or out of capillary: interstitial oncotic pressure

Answer 16

Out

Question 17

3 things causing hypoxic vasoconstriction of pulmonary vasculature

Answer 17

1. Hypoxia
2. Hypercapnia (increased CO2)
3. Acidosis
   (remember CO2 and H+ right shift O2-Hb curve)

Question 18

What is the purpose of hypoxic vasoconstriction?

Answer 18

Reduce PBF to alveoli that are not well ventilated (hence hypoxic) to not waste blood flow

Question 19

Mechanism of hypoxic vasoconstriction

Answer 19

O2 diffuses from alveoli to SMC of arteriole; if SMC senses PO2<70, depolarizes; Ca2+ entry; constriction

Question 20

Vasoconstriction (increases, decreases) resistance, thus (increases, decreases) flow

Answer 20

Increases
Decreases (Q=P/R)

Question 21

Name 2 conditions under which hypoxic vasoconstriction would be global

Answer 21

1. High altitude

2. Fetal circulation (doesn’t breathe, so PO2<70)

Question 22

Average V/Q

Answer 22

0.8

80% of blood is ventilated

Question 23

O2 v. CO2 content: high V/Q

Answer 23

More O2

Question 24

O2 v. CO2 content: low V/Q

Answer 24

More CO2

Question 25

High or low V/Q: Apex

Answer 25

High; perfusion is low at apex

Question 26

High or low V/Q: Base

Answer 26

Low; perfusion is high at base

Question 27

O2 v. CO2: Hypoperfusion

Answer 27

More O2

Question 28

O2 v. CO2: Hypoventilation

Answer 28

More CO2

Question 29

Positive A-a gradient means:

Answer 29

Problem with perfusion (a)

Question 30

Negative A-a gradient means:

Answer 30

Problem with ventilation (A)

Question 31

Supplemental O2 will not fully correct:

Answer 31

Shunt

Question 32

Which affects PACO2 more: V/Q mismatch or shunt?

Answer 32

NEITHER!!!!

Question 33

Only thing that affects PACO2

Answer 33

Production of CO2 relative to ventilation of CO2

remember alveolar gas equation: PaCO2 = VCO2/Valv

Question 34

How to treat if PaO2 is low and PaCO2 is low

Answer 34

Supp O2

Question 35

How to treat if PaO2 is low and PaCO2 is high

Answer 35

Hyperventilate