Ventilation and Compliance

Question 1

Define tidal volume and state the normal TV

Answer 1

Volume of air breathed in and out in one breath

500ml

Question 2

Define expiratory reserve volume and state normal ERV

Answer 2

Maximum volume of air expelled from lungs at end of normal expiration
1100ml

Question 3

Define inspiratory reserve volume and state normal IRV

Answer 3

Maximum volume of air able to draw into lungs at the end of a normal inspiration
3000ml

Question 4

Define residual volume and state normal RV

Answer 4

Volume of gas lift in lungs at end of normal inspiration

1200ml

Question 5

Define vital capacity and state normal VC

Answer 5

TV+ERV+IRV

4600ml

Question 6

Define total lung capacity and state normal TLC

Answer 6

VC+RV

5800ml

Question 7

Define inspiratory capacity and state normal IC

Answer 7

TV+IRV

3500ml

Question 8

Define functional residual capacity and state normal FRC

Answer 8

ERV+RV

3300ml

Question 9

Define FEV1

Answer 9

Forced Expiratory Volume in one second

Question 10

Define FEV1/FEV

Answer 10

Fraction of FEV expired in 1 second

Question 11

Define pulmonary (minute) ventilation

Answer 11

Movement of air in and out lungs

Question 12

Define alveolar ventilation and how it is measured

Answer 12

Fresh air available to alveoli and thus exchanged.

Measured in L/min

Question 13

Explain the concept of anatomical dead space and alveolar ventilation in terms of volumes

Answer 13

The air in airways above alveoli is stale air and only the air in alveoli is exchanged.
For every 500ml of air, 350mls is fresh air that is exchanged and 150mls is stale air in the anatomical dead space

Question 14

State how alveolar ventilation is calculated

Answer 14

(Tidal Volume - 150) x Respiratory Rate

NEED TO DIVIDE BY 1000 TO GET IN L/min

Question 15

Calculate normal ventilation

Answer 15

(500-150) x 12 = 4200 = 4.2L/min

Question 16

Calculate hypoventilation if respiratory rate is 20 breaths per minute and tidal volume is 300ml

Answer 16

(300-150) x 20 = 3000 = 3 L/min

Question 17

Calculate hyperventilation if RR is 8 breaths per minute and tidal volume is 750ml

Answer 17

(750-150) x 8 = 4800 = 4.8L/min

Question 18

Define partial pressure

Answer 18

The pressure of gas in gas mixture equivalent to the percentage of that gas in that mixture multiplied by the pressure of the whole gas mixture.
E.g. if 21% of a mixture is O2 and the pressure of the whole mixture is 760mmHg then the partial pressure of O2 in that mixture will be 160mmHg

Question 19

What is the consequence of all gas molecules exerting the same pressure?

Answer 19

This means that pressure increases if the concentration of gases in a mixture increases.

Question 20

Define normal atmospheric PO2 and normal alveolar PO2

Answer 20

Atmospheric = 160mmHg
Alveolar = 100mmHg

Question 21

Define normal alveolar PO2 and normal alveolar PCO2 in mmHg and pKa which are mirrored in arterial blood

Answer 21

PO2 = 100mmHg / 13.3pKa
PCO2 = 40mmHg / 5.3pKa

Question 22

State the partial pressures of O2 and CO2 in hypo and hyperventilation in mmHg

Answer 22

HYPOVENTILATION
PO2 = 30mmHg PCO2 = 100mmHg

HYPERVENTILATION
PO2 = 120mmHg PCO2 = 100mmHg

Question 23

What is surfactant?

Answer 23

Detergent like substance made by Type II alveolar cells

Reduces surface tension.

Question 24

Define surface tension and state it’s effect on alveoli

Answer 24

Surface tension is the attraction of water molecules together when there is a water-air interface.
This creates an inwardly directed pressure which causes the alveoli to collapse

Question 25

Describe how surfactant reduces the work of breathing

Answer 25

Surfactant reduces surface tension thus increasing compliance and reducing the tendency of the lungs to recoil (and the alveoli collapsing)

Question 26

Why is surfactant more effective in small alveoli?

Answer 26

Surfactant is more effective in small alveoli because surfactant molecules are closer together making it more concentrated.

Question 27

How does the Law of LaPlace explain why air is more likely to flow into large, as opposed to small alveoli? How does surfactant equalise this?

Answer 27

Law of LaPlace P=2T/r which means that pressure is greater in the smaller alveolus because the radius is less. This means that air is more likely to flow into larger alveoli at a lower pressure which reduces the SA that can absorb air. Surfactant lowers the surface tension making the smaller alveoli easier to inflate by reducing their tendency to recoil.

Question 28

Define compliance

Answer 28

Change in volume relative to the change in pressure. | The stretchability of the lungs

Question 29

When is compliance high?

Answer 29

When there is a large increase in volume for a small decrease in intrapleural pressure

Question 30

When is compliance low?

Answer 30

When there is a small increase in volume for a large decrease in in intrapleural pressure

Question 31

Why is a greater change in pressure from required in inflate the lungs in comparison to deflating them?

Answer 31

Because the surface tension needs to be overcome during inspiration

Question 32

What is the effect of restrictive lung diseases on compliance

Answer 32

Fibrosis reduces compliance

Question 33

What is the effect of obstructive lung disease such as emphysema on compliance?

Answer 33

Loss of surface tension due to alveolar loss leads to highly compliant but expiration is much more difficult

Question 34

Define the normal FEV1 to FVC ratio

Answer 34

4/5=80%

Question 35

Describe the FEV1 to FVC ratio in obstructive lung disease

Answer 35

1.3/3.1=43% Airway resistance is increased so air is obstructed on expiration. Air gets out much more slowly so FEV1 is reduced. FVC is also reduced to a greater extent and FRC will be higher

Question 36

Describe the FEV1 to FVC ratio in restrictive lung disease

Answer 36

2.8/3.1 =90% Difficulty in lung expansion due to fibrosis. Lack of surfactant means that the total volume is reduced and large volume can't be expelled in 1 second so the ratio stays the same. This is a limitation of spirometry

Question 37

Define forced expiratory flow (FEF25-75)

Answer 37

Air expired in 1 second in middle of FVC. Correlates with FEV1 but changes more striking.

Question 38

List the three factors that determine compliance

Answer 38

Elastic forces Surface tension at alveolar air-liquid interface Airway resistance

Question 39

How do ventilation and compliance vary from apex to base?

Answer 39

At the base of the lung the volume change is greater for a given change in pressure Alveoli are also more compliant at the base of the lung than at the apex because they are more compressed between the weight of the lung and the diaphragm meaning a small change in ip pressure will have the greatest effect on volume here.