Respiratory physiology 3

Question 1

In each alveolar unit, the ventilation to perfusion ratio of each alveolar unit is determined by the

Answer 1

relative pressures between the alveolus (PA), arterial capillary (Pa), venous capillary (Pv), and the interstitial space (Pist)

Question 2

Describe zone 1

Answer 2

dead space
PA>Pa>Pv

Question 3

describe zone 2

Answer 3

waterfall
Pa>PA>Pv

Question 4

Describe zone 3

Answer 4

Shunt: Pa>Pv>PA

Question 5

Describe zone 4

Answer 5

Pulmonary edema: Pa>Pist>Pv>PA

Question 6

Anatomic shunt describes any

Answer 6

venous blood that empties directly into the left side of the heart

Question 7

Sites that contribute to the normal anatomic shunt include the

Answer 7

thebesian, bronchiolar and pleural veins

Question 8

Describe ventilation & perfusion in zone 1.

Answer 8

There is ventilation but there is no perfusion

Question 9

Where does zone 1 occur?

Answer 9

this zone usually does not occur in normal lung

Question 10

Zone 1 is increased by

Answer 10

hypotension, pulmonary embolus, or excessive airway pressure

Question 11

Describe ventilation and perfusion in zone 2.

Answer 11

V/Q=1
blood flow is directly proportional to the difference in Pa-PA

Question 12

Describe perfusion and ventilation in zone 3

Answer 12

Most zone 3 units are “shunt-like”- they are better perfused than they are ventilated (V<Q)

Question 13

What are the two ways in which pulmonary edema in zone 4 can develop?

Answer 13

1. fluid is pushed across the capillary membrane y a significant increase in capillary hydrostatic pressure (fluid overload, mitral stenosis)
2. fluid is pulled across the capillary membrane by a profound reduction in pleural pressure (laryngospasm or negative pressure pulmonary edema)

Question 14

A patient is breathing room air at sea level. The arterial blood gas reveals a PaO2 of 60 mmHg and a PaCO2 of 70 mmHg. Calculate the patient’s alveolar oxygen concentration.

Answer 14

62 mmHg
Alveolar oxygen= FiO2 x (Pb-PH2O)- (PaCOs/RQ)
0.21 x(760-47)- (70/0.8)= 62

Question 15

The alveolar gas equation is used to estimate the

Answer 15

partial pressure of oxygen in the alveoli

Question 16

The alveolar gas equation tells us the maximal ____________ that can be achieved at a given ______________

Answer 16

PAO2 at a given FiO2

Question 17

What 3 points does the alveolar gas equation help us understand?

Answer 17

1. hypoventilation can cause hypoxemia & hypercarbia
2. supplemental oxygen can easily reverse hypoxemia but it does nothing to reverse hypercarbia
3. hypercarbia can go undetected in the patient breathing supplemental oxygen

Question 18

PH2O is assumed to be

Answer 18

47 mmHg

Question 19

The respiratory quotient is assumed to be

Answer 19

0.8

Question 20

An RQ > 1 suggests

Answer 20

lipogenesis which occurs with overfeeding

Question 21

An RQ of 0.7 suggests

Answer 21

lipolysis which occurs with starvation

Question 22

Causes of an increased A-a gradient include: (select 2)
a. hypoventilation
b. V/Q mismatch
c. hypoxic mixture
d. diffusion limitation

Answer 22

B. V/Q mismatch
D. diffusion limitation

Question 23

The A-a gradient is the difference between

Answer 23

alveolar oxygen (PAO2) and arterial oxygen (PaO2)

Question 24

Calculating the A-a gradient helps us diagnose the cause of

Answer 24

hypoxemia by indicating the amount of venous adminixture

Question 25

To complete the A-a gradient calculation, you’ll need to use the

Answer 25

alveolar gas equation (for PAO2) and obtain an ABG (for PaO2)

Question 26

Etiologies of hypoxemia with a normal A-a gradient include

Answer 26

low FiO2 & hypoventilation

Question 27

Etiologies of hypoxemia with an increased A-a gradient include

Answer 27

diffusion limitation, V/Q mismatch, and shunt

Question 28

Supplemental oxygen can improve oxygenation in all cases of hypoxemia, with the exception of

Answer 28

shunt

Question 29

The five causes of hypoxemia include

Answer 29

reduced FiO2
hypoventilation
V/Q mismatch
diffusion impairment
shunt

Question 30

Examples of reduced FiO2 include

Answer 30

hypoxemic mixture
oxygen pipeline failure
high altitude

Question 31

Examples of hypoventilation include

Answer 31

opioid overdose
residual anesthetic agent
residual NMB
neuromuscular disease
obesity hypoventilation

Question 32

Examples of V/Q mismatch include

Answer 32

COPD
One-lung ventilation
impaired hypoxic pulmonary vasoconstriction
embolism

Question 33

Examples of diffusion impairment include

Answer 33

pulmonary fibrosis
emphysema
interstitial lung disease

Question 34

Examples of shunt include

Answer 34

atelectasis
pneumonia
bronchial intubation
intracardiac shunt

Question 35

When breathing room air, the normal A-a gradient is

Answer 35

less than 15 mmHg

Question 36

Things that increase the A-a gradient include

Answer 36

aging
vasodilators
right-to left shunt
diffusion limitation

Question 37

Describe why aging increase the A-a gradient

Answer 37

closing capacity increases relative to FRC

Question 38

Describe why vasodilators increase the A-a gradient

Answer 38

decreased hypoxic pulmonary vasoconstriction

Question 39

Describe why right to left shunts increase the A-a gradient

Answer 39

atelectasis, pneumonia, bronchial intubation
intracardiac defect

Question 40

Explain why diffusion limitation increase the A-a gradient

Answer 40

alveolocapillary thickening hinders O2 diffusion

Question 41

Shunt increases 1% for every __________ of A-a gradient

Answer 41

20 mmHg