Respiratory: Physiology - Ventilation

Question 1

Normal tidal volume

Answer 1

500ml

Question 2

Normal minute ventilation (assume RR 15/min)

Answer 2

7.5L/min

Question 3

Normal volume of anatomic dead space

Answer 3

150ml

Question 4

Normal pulmonary blood flow

Answer 4

5L/min

Question 4

Normal volume pulmonary capillary blood

Answer 4

70ml

Question 5

Normal alveolar ventilation

Answer 5

5.25L/min

Question 6

What lung volumes cannot be measured using a spirometer?

Answer 6

TLC, FRC, RV

Question 7

Normal total lung capacity

Answer 7

6L

Question 8

Normal vital capacity

Answer 8

4.8L

Question 9

Normal residual volume

Answer 9

1.2L

Question 10

Normal inspiratory reserve volume

Answer 10

3L

Question 11

Normal expiratory reserve volume

Answer 11

1.2L

Question 12

By which two methods can FRC, RV and TLC be measured?

Answer 12

1. Helium dilution
2. Body plethysmography

Question 13

Describe the process of helium dilution. Why is helium chosen?

Answer 13

Helium chosen as is insoluble in blood
Concentration of helium is measured before and after inspiration (concentration equilibrates between spirometer and lungs)
V2 = V1 x [(C1-C2)/C2]

Question 14

Describe the process of body plethysmography. Which law does it rely on?

Answer 14

Pt inhales against closed mouthpiece, reducing pressure in lungs and therefore increasing pressure in closed box
Uses Boyle’s law which states that pressure x volume is constant at constant temperature

Question 15

Boyle’s law

Answer 15

Pressure x volume is constant at constant temperature

Question 16

Which is more accurate for measuring TLC in diseased lung: helium dilution or body plethysmography?

Answer 16

Body plethysmography: can measure “trapped air”

Question 17

Why is inspired volume slightly greater than expired volume?

Answer 17

More O2 goes in than CO2 out

Question 18

How can alveolar ventilation be determined?

Answer 18

CO2 production divided by fractional CO2 concentration in expired gas

Question 19

What is the difference between anatomic and physiologic dead space? When do these differ?

Answer 19

Anatomic: volume of conducting airways
Physiologic: volume of gas not equilibrating with blood
Usually equal in normal healthy lung, physiologic increased in acute and chronic disease states

Question 20

Which method (equation) is used to calculate physiologic dead space?

Answer 20

Bohr’s method
(VD/VT) = [(PACO2 - PECO2)/PACO2]

PACO2 = PaCO2 in healthy people

Question 21

How is anatomic dead space measured?

Answer 21

Via Fowler’s method
Following test inspiration of 100% O2, N2 rises to a plateau representing pure alveolar gas during expiration (dead space washed out)

Question 22

Describe regional differences in ventilation

Answer 22

Lower regions of lung ventilate better than upper

Question 23

What is the reason for regional differences in ventilation?

Answer 23

Intrapleural pressures are lower in upper lung to counteract the effects of gravity and weight of the lung
Higher intrapleural pressures in lower lung causes reduced volumes at rest, and therefore increased compliance of this portion of lung

Question 24

Describe the difference in intrapleural pressure between upper and lower lung

Answer 24

Upper: -10mmHg
Lower: -2.5mmHg

Question 25

List five factors that increase CO2 production

Answer 25

1. Exercise
2. Nutritional intake
3. Fever
4. Infection
5. Seizures

Question 26

List two factors that decrease CO2 production

Answer 26

1. Hypothermia
2. Fasting