VQ ratios and expired gases - exam 3

Question 1

Normal V/Q ratio

Answer 1

4200 mL air/5000 mL blood = 0.80

Question 2

If there is an issue with ventilation, PO2 will be ___ and PCO2 will be ___

Answer 2

PO2 40 mmHg, PCO2 45mmHg - match the blood gases coming into the pulmonary artery (same as blood leaving the alveoli - no gas exchange)

Question 3

If there is an issue with perfusion, PO2 will be ___ and PCO2 will be ___

Answer 3

PO2 150 mmHg, PCO2 0 mmHg - same as inspired air

Question 4

If there is an issue with ventilation, the V/Q ratio will ________

Answer 4

decrease

Question 5

If there is an issue with perfusion, the V/Q ratio will ________

Answer 5

increase

Question 6

The upper and lower limits of the V/Q ratio are _____

Answer 6

infinity and zero

Question 7

a way to describe blood flow through a non-ventilated alveolus is a _______

Answer 7

shunt

Question 8

a way to describe ventilation through an unperfused alveolus is _______

Answer 8

dead space

Question 9

an area with more perfusion would have what changes to O2 and CO2?

Answer 9

lower oxygen, higher CO2

Question 10

an area with more ventilation would have what changes to O2 and CO2?

Answer 10

higher oxygen, lower CO2

Question 11

The base of the lung has _____ ventilation and ____ blood flow compared to the apex of the lung

Answer 11

more and more

Question 12

at the base of the lung, ventilation is _____ than blood flow

Answer 12

less

Question 13

at the apex of the lung, ventilation is _____ than blood flow

Answer 13

more

Question 14

between blood flow and ventilation, which has greater regional differences?

Answer 14

blood flow

Question 15

the top of the lung compared to the bottom CO2 vs O2

Answer 15

base - lower O2, higher CO2
top - higher O2, lower CO2

Question 16

Compare the effects of age on V/Q ratios

Answer 16

younger (22 yoa) - good V/Q matching
older (44 yoa) - poorer V/Q ratios; higher blood flow and lower ventilation

Question 17

Anesthesia results in what change to the V/Q ratio?

Answer 17

atelectasis/dead space - dec ventilation

Question 18

What can resolve the negative changes of anesthesia to V/Q matching?

Answer 18

PEEP

Question 19

describe LaPlace’s Law

Answer 19

ventilation will be uneven: air will move to the alveoli with more air/less pressure (move from smaller to larger spheres) until the larger alveoli is 80-90% full

Question 20

When is LaPlace’s law applicable?

Answer 20

Unhealthy patients - don’t have surfactant

Question 21

How does surfactant affect LaPlace’s law?

Answer 21

surfactant is less spread out with less air in an alveolus, resulting in a higher concentration of surfactant to surface area, dec surface tension, corrects LaPlace’s law - healthy patients

Question 22

anatomic dead space is usually _____ mL

Answer 22

150 mL or 1 mL/lb of ideal body weight

Question 23

mixed expired gas is…?

Answer 23

a collection of the entire expired breath; including alveolar air and dead space air

Question 24

What are the normal values of oxygen, CO2, nitrogen, and water of mixed expired air?

Answer 24

PEO2: 115-120 mmHg
PECO2: 27-28 mmHg
PEN2: 566 mmHg
PEH2O: 47 mmHg

Question 25

If there is dead space in the lungs, mixed expired air will have what change?

Answer 25

dec PECO2

Question 26

How is PECO2 calculated?

Answer 26

1. Determine the partial pressure of the gas (40/760 = 5.3%) 2. Multiply by volume (5.3% * 350 mL = 18.42) 3. volume of CO2/total volume = new concentration of gas (18.42/500 = 3.7%) 4. new concentration of gas * total pressure = PECO2 (3.7%*760 = 28 mmHg)