Ventilation and Compliance

Question 1

Tidal volume (TV)

Answer 1

The volume of air breathed in or out of the lungs at each breath (500ml).

Question 2

Expiratory reserve volume (ERV)

Answer 2

The maximum volume of air that can be expelled from the lungs at the end of a normal expiration (1100ml).

Question 3

Inspiratory reserve volume (IRV)

Answer 3

The maximum volume of air that can be drawn into the lungs at the end of a normal inspiration (3000ml).

Question 4

Residual volume (RV)

Answer 4

The volume of gas in the lungs at the end of a maximal expiration (1200ml).

Question 5

Vital capacity (VC)

Answer 5

VC = TV + IRV + ERV

Question 6

Total lung capacity (TLC)

Answer 6

TLC = VC + RV

Question 7

Inspiratory capacity (IC)

Answer 7

IC = TV + IRV

Question 8

Functional residual capacity (FRC)

Answer 8

FRC = ERV + RV

Question 9

FEV1

Answer 9

Forced expired volume in 1 second.

Question 10

FEV1:FVC

Answer 10

Fraction of FVC in 1 second.

Question 11

Describe pulmonary (minute) ventilation

Answer 11

Total air movement into and out of the lungs (functionally insignificant).

Question 12

Describe alveolar ventilation

Answer 12

Fresh air getting into alveoli and thus, available for gas exchange (functionally significant).

Question 13

Define partial pressure

Answer 13

The pressure of a gas in a mixture of gases is equivalent to there percentage of that particular gas in the entire mixture multiplied by the pressure of the whole gaseous mixture.
All gas molecules exert the same pressure, so partial pressure increases with increasing conc. of gas mixture.

Question 14

What is the normal value for the partial pressure of oxygen in alveolar and arterial gas?

Answer 14

O2 = 100mmHg, 13.3kPa

Question 15

What is the normal value for the partial pressure of carbon dioxide in alveolar and arterial gas?

Answer 15

CO2 = 40mmHg, 5.3kPa

Question 16

State the role of pulmonary surfactant

Answer 16

Surfactant is a detergent-like fluid produced by type II alveolar cells.

• Reduces surface tension on the alveolar surface membrane, thus reducing tendency for alveoli to collapse
• Increases distensibility (lung compliance)
• Reduces lung’s tendency to recoil
• Makes work of breathing easier

Question 17

State the Law of Laplace

Answer 17

P = 2T/r

Where P = pressure, T = surface tension and r = radius

Question 18

Define compliance

Answer 18

Change in volume relative to change in pressure. It represents the stretchability of lungs, not elasticity.

Question 19

List factors that affect compliance

Answer 19

Changes in disease states/age.
Emphysema (obstructive) - loss of elastic tissue means expiration requires effort.
Fibrosis (restrictive) - inert fibrous tissue means effort of inspiration increases.

Question 20

Describe the pressure-volume relationship in terms of respiration

Answer 20

In inspiration, a bigger change in pressure is required to reach a particular lung volume, than to maintain that volume in expiration. This is because the work of inspiration is recovered in expiration due to elastic recoil.

Question 21

Summarise the basic characteristics of obstructive lung disease

Answer 21

• Obstruction of air flow, especially on expiration
• Increased airway resistance
  e. g. asthma, COPD, chronic bronchitis, emphysema

Question 22

Summarise the basic characteristics of restrictive lung disease

Answer 22

• Loss of lung compliance: lung stiffness, incomplete lung expansion
  e. g. pulmonary fibrosis, IRDS, oedema, pneumothorax

Question 23

Describe the tests used to identify abnormal lung function

Answer 23

Spirometry;

• Static: consider only volume exhaled
• Dynamic: consider time to exhale a certain volume
• Can measure TV, IRV, ERV, IC and VC

Question 24

How does an obstructive lung disease affect spirometry?

Answer 24

• Rate of exhalation much slower
• FRC is reduced
• FEV is reduced more so than FRC, due to major effect on airways
• FEV1:FRC is reduced

Question 25

How does an restrictive lung disease affect spirometry?

Answer 25

• Absolute rate of air flow is reduced
• Total volume is reduced due to restricted lung expansion
• Ratio remains constant or increases
• FEV1:FRC remains constant, thus is not always indicative of good health