11: Pulmonary Blood Flow And Ventilation

Question 1

PaO2 in arteries in systemic vs pulmonary circulation

Answer 1

Pulmonary PaO2: 40 mmHg

Systemic PaO2: 100 mmHg

Question 2

Pulmonary vs systemic circulation’s response to hypoxia

Answer 2

Pulmonary: vasoconstriction
Systemic: vasodilate

Question 3

Purpose of hypoxic vasoconstriction in lungs

Answer 3

Directs blood to areas of the lungs with better oxygenation

Question 4

Mechanism of hypoxic vasoconstriction

Answer 4

Myogenic - SM vasoconstriction without innervation

Question 5

Mechanism of hypoxia leading to SM contraction

Answer 5

1. Hypoxia -> decreased NADH (energy in general)
2. Low NADH -> decreases leak channels -> less K leaves cell -> depol occurs
3. Depol causes increased L-type Ca channels -> SM contraction

Question 6

Bronchial capillaries (extra-alveolar caps)

Answer 6

Deliver O2 and CO2 to the tissue of the lungs

Question 7

Two paths for bronchial capillaries to return to the heart

Answer 7

1. Flow into azygos vein and other nearby veins -> RV

2. Flow into pulmonary veins -> creates a venous admixture

Question 8

Three things that cause decreases pulmonary vascular resistance in COPD

Answer 8

1. Gas trapping
2. Decreased surface area
3. Hypoxic vasoconstriction

Question 9

Three big chemical modulators of pulmonary blood flow

Answer 9

1. NO
2. Endothelin 1
3. Thromboxane A2

Question 10

What makes NO and what does it cause?

Answer 10

Made by endothelium -> causes SM relaxation and vasodilation

Question 11

Endothelin 1 and thromboxane 2: where they’re made and the function

Answer 11

Made in lungs -> vasoconstrction in pathological conditions

Question 12

What does ACE inactivate?

Answer 12

Bradykinin

Question 13

ACE inhibitors side affect and why

Answer 13

Can cause a cough bc of an accumulation of bradykinin

Question 14

What type of metabolism do the lungs play a role in? What are examples of this?

Answer 14

Metabolism of arachidonic acid metabolites - leukotrienes, prostaglandins E2 and FA, thromboxane a2

Question 15

What is the alveolar gas equation used to calculate?

Answer 15

What inspired O2 is needed to produce a desired alveolar O2 level

Question 16

FiO2

Answer 16

Fraction of inspired O2, is 21% unless otherwise specified

Question 17

What does an increase in A-a O2 gradient indicate?

Answer 17

Diffusion impairment in the alveoli

Question 18

What does it mean if the A-a gradient is normal, but PaO2 and PAO2 are both low

Answer 18

There is a problem outside of the lungs (ex: the pt may be hypoventilating)

Question 19

Intra pleural pressure in lung’s apex vs base

Answer 19

Apex: more negative pressure bc of less intrapleural fluid (-10 cm H2O)
Base: less negative pressure bc of more intrapleural fluid + the force of gravity (-2 cm H2O)

Question 20

V/Q ratio in apex vs middle vs base

Answer 20

Apex: V/Q ratio high (PaO2 = 130, PaCO2 = 28)
Middle: V/Q is about 0.8 (nl)
Base: V/Q ratio is low (PaO2 = 89, PaCO2 = 42)

Question 21

VQ ratio in a space with less alveoli present (ex: in COPD)

Answer 21

High V/Q

Question 22

Mechanism to minimize differences in V/Q ratios in the different zones of the lung

Answer 22

Hypoxic vasoconstrction