2. Ventilation And Lung Mechanics

Question 1

What is the range of normal pO2?

Answer 1

9.3-13.3 kPa

Question 2

What is the normal range of pCO2?

Answer 2

4.7-6 kPa

Question 3

What is lung parenchyma?

Answer 3

The portion of the lungs involved in gas exchange.

Question 4

What is the definition of resting end-respiratory level/functional residual capacity?

Answer 4

The volume of air in the lungs at the end of a passive exhalation.

Question 5

What is the resting end-respiratory level/functional residual capacity determined by?

Answer 5

The balance of elastic forces of the chest wall, favouring outward expansion, and the elasticity and surface tension of the lung, favouring a smaller lung volume.

Question 6

What is the lung sealed to the chest wall by?

Answer 6

The pleural membranes.

Question 7

The pressure within the pleural space is always slightly negative. However, when is it more negative - at end-inspiration or end-expiration?

Answer 7

At end-inspiration

Question 8

What leads to a negative pressure in the pleural space?

Answer 8

The tension between the elastic forces acting to make the ribcage spring out and the elastic recoil of the lung.

Question 9

Name the 5 accessory muscles of inspiration

Answer 9

Sternocleidomastoid.
Scalene.
Pectoralis major and minor.
Trapezius.

Question 10

Name the 2 accessory muscles of expiration

Answer 10

Internal intercostals.

Muscles of the abdominal wall.

Question 11

In an older adult, the resting expiratory level (FRC) is relatively higher than in a younger person. Why is this?

Answer 11

Lungs lose elasticity, so recoils in less on expiration.

Question 12

What is lung compliance?

Answer 12

The relationship between pressure and volume.

Question 13

What condition is caused by lowered lung compliance?

Answer 13

Fibrosis.

Question 14

What condition is caused by increased lung compliance?

Answer 14

Emphysema

Question 15

What is surfactant?

Answer 15

Mixture of lipids and proteins, secreted by alveolar cells.

Question 16

What does surfactant do?

Answer 16

Acts to reduce surface tension allowing the lungs to inflate more easily (increased compliance), helps regulate alveolar size, and prevents alveolar collapse.

Question 17

Production of surfactant begins between what weeks of gestational age? When is it adequate?

Answer 17

25-28 weeks.

Adequate at 35 weeks.

Question 18

In what disease is surfactant production diminished?

Answer 18

Acute respiratory distress syndrome (ARDS).

Question 19

Why is the pressure in small and large alveoli the same in the lungs, so that small alveoli do not collapse into the large ones?

Answer 19

Surfactant spreads more thinly across the surface of the large alveoli, so surfactant is less effective and surface tension increases, making inflation harder, and pressure remains the same in both large and small alveoli.

Question 20

How is minute ventilation calculated?

Answer 20

Respiratory frequency x tidal volume.

Question 21

Why is not all the respire volume available for gas exchange?

Answer 21

Physiological dead space - combination of:
Anatomical dead space - upper respiratory tract between mouth and respiratory bronchioles.
Alveolar dead space - alveolar that are ventilated but not perfused or very poorly perfused.

Question 22

What is the rough volume of anatomical dead space? Therefore what is the tidal volume entering the gas-exchange region of the lung?

Answer 22

150ml.

350ml.

Question 23

How is alveolar ventilation calculated?

Answer 23

Respiratory frequency x volume available for gas exchange (tidal volume - anatomical dead space)

Question 24

What structures form the conducting airways? What division numbers are these up to?

Answer 24

Trachea, bronchi, bronchioles, terminal bronchial, transitional bronchioles.
Divisions 1-14.

Question 25

What structures form the acinar airways? What division numbers are these between?

Answer 25

Transitional bronchioles, respiratory bronchioles, alveolar ducts, alveolar sacs.
Divisions 15-23.

Question 26

Increased mucus production increases airway resistance leading to what disease?

Answer 26

Chronic bronchitis.

Question 27

Hypertrophy of the smooth muscle and/or oedema increases airway resistance leading to what disease?

Answer 27

Asthma

Question 28

Loss of radial traction (meaning the airways are not help open as much) increases airway resistance leading to what disease?

Answer 28

Emphysema

Question 29

Where in the bronchial tree is the main site of airways resistance?

Answer 29

Upper respiratory tract

Question 30

A small change in what element of the respiratory tract makes a big difference to the resistance?

Answer 30

Radius