Respiratory physiology 2

Question 1

The Vd/Vt ratio tells us the percentage of the

Answer 1

total tidal volume that is allocated to dead space

Question 2

In the spontaneously ventilating patient, the Vd/Vt ratio approximates

Answer 2

0.33

Question 3

In the mechanically ventilated patient, the Vd/Vt ratio approximates

Answer 3

0.50

Question 4

Factors that increase the ratio of Vd to Vt include

Answer 4

a facemask
atropine
neck extension

Question 5

Factors that decrease the ratio of Vd to Vt include

Answer 5

ETT
LMA
neck flexion

Question 6

Physiologic dead space can be calculated with the

Answer 6

Bohr equation
compares the partial pressure of CO2 in the blood vs. the partial pressure of CO2 in exhaled gas

Question 7

The most common cause of increased Vd/Vt under general anesthesia is a reduction in

Answer 7

cardiac output

Question 8

What pathophysiology will increase Vd?

Answer 8

decreased cardiac output
COPD
PE (thrombus, air, amniotic fluid)

Question 9

What surgical position will increase Vd?

Answer 9

sitting

Question 10

What surgical position will decrease Vd?

Answer 10

supine
Trendelenburg (head down)

Question 11

Does increasing the length of the circuit increase dead space?

Answer 11

No; in the circle system dead space begins at the y-piece and anything proximal does not influence dead space

Question 12

What is the A-a gradient equation?

Answer 12

PAO2-PaO2

Question 13

A patient is in the sitting position. When compared to the apex of the lung, which of the following are higher in the base?
a. blood flow
b. partial pressure of alveolar oxygen
c. V/Q ratio
d. partial pressure of alveolar carbon dioxide

Answer 13

a. blood flow
d. partial pressure of alveolar carbon dioxide

Question 14

What is the normal V/Q ratio?

Answer 14

0.8

Question 15

Alveolar compliance is defined as

Answer 15

a change in alveolar volume for a given change in pressure

Question 16

Alveolar ventilation is greatest in the lung

Answer 16

base due to greater alveolar compliance

Question 17

Alveolar perfusion is greatest in the lung

Answer 17

base due to higher pulmonary blood flow

Question 18

In the sitting position, which lung region is the dependent lung and which is the non-dependent lung?

Answer 18

base- dependent
apex- non-dependent

Question 19

Identify the statements that represent the MOST accurate understanding of V/Q mismatch. (Select 2)
a. bronchioles constrict to minimize zone 1
b. the A-a gradient is usually small
c. blood passing through under-ventilated alveoli tends to retain CO2
d. hypoxic pulmonary vasoconstriction minimizes dead space

Answer 19

a. bronchioles constrict to minimize zone 1
c. blood passing through underventilated alveoli tends to retain CO2

Question 20

The normal ratio of ventilation to perfusion is

Answer 20

0.8

Question 21

Dead space occurs when there is

Answer 21

ventilation but no perfusion (V/Q= infinity)

Question 22

Shunt occurs when there is

Answer 22

perfusion but no ventilation (V/Q= 0)

Question 23

The most common cause of hypoxemia in the PACU is

Answer 23

atelectasis

Question 24

Atelectasis leads to

Answer 24

right to left shunt
V/Q mismatch
hypoxemia

Question 25

Patients with V/Q mismatch tend to have more trouble with _________ than with ______________

Answer 25

oxygenation than with CO2 elimination

Question 26

CO2 retention suggests a

Answer 26

severe V/Q mismatch

Question 27

Treatment for atelectasis includes

Answer 27

humidified O2 & maneuvers designed to reopen the airways (mobility, coughing, deep breathing, and incentive spirometry)

Question 28

What happens in under-ventilated alveoli?

Answer 28

blood passing through underventilated alveoli tends to retain CO2 and is unable to take in enough oxygen

Question 29

What happens in over-ventilated alveoli?

Answer 29

blood passing through over-ventilated alveoli tends to give off an excessive amount of CO2; remember that CO2 diffuses 20 times faster than oxygen

Question 30

To combat dead space is zone 1, the body

Answer 30

constricts the bronchioles to minimize ventilation of poorly perfused alveoli

Question 31

To combat shunt in zone 3, the body engages

Answer 31

hypoxic pulmonary vasoconstriction to reduce pulmonary blood flow to the poorly ventilated alveoli

Question 32

Variables described by the law of LaPlace include all of the following EXCEPT:
a. tension
b. pressure
c. radius
d. density

Answer 32

d. density

Question 33

The law of Laplace describes the relationship between

Answer 33

pressure, radius, and wall tension

Question 34

____ equalizes the effect of surface tension by keeping alveolar pressures constant

Answer 34

Surfactant

Question 35

Surfactant prevents

Answer 35

smaller alveoli from collapsing and emptying into larger alveoli

Question 36

What is the law of Laplace for spherical shapes?

Answer 36

P= 2T/R

Question 37

The tendency of an alveolus to collapse is directly proportional to

Answer 37

surface tension (more tension= more likely to collapse)

Question 38

The tendency of an alveolus to collapse is inversely proportional to

Answer 38

alveolar radius (smaller radius= more likely to collapse)

Question 39

A thin layer of _____ coats the alveoli, increasing _______ & promoting alveolar collapse

Answer 39

water; surface tension

Question 40

________________ produce surfactant

Answer 40

Type 2 pneumocytes

Question 41

When do type 2 pneumocytes produce surfactant?

Answer 41

between 22-26 weeks with peak production occurring at 35-36 weeks

Question 42

Fetal lung maturity (in the setting of premature labor) can be hastened by

Answer 42

corticosteroids

Question 43

What is the law of Laplace for cylinder shapes?

Answer 43

tension = pressure x radius
think blood vessels