Lung Function

Question 1

Why is it important to know about the respiratory system ?

Answer 1

• integral to safe dental treatment of patients with respiratory problems
• general anaesthetic can lead to hypoxia
• analgesics and narcotics are respiratory depressants
• drilling of the teeth can cause asthma attacks

Question 2

What is the function of the respiratory system ?

Answer 2

• gas exchange - intake of oxygen and removal of carbon dioxide
• contributes to regulation of blood pH
• filters and heats inspired air
• metabolises inhaled chemicals
• receptors for sense of smell

Question 3

What are the functions of the elastic fibres on the alveoli ?

Answer 3

They give the lungs elastic recoil

Question 4

Describe the structure of the respiratory system

Answer 4

• trachea > bronchi > bronchioles > terminal bronchioles > respiratory bronchioles > alveolar ducts > alveolar sacs
• 2 zones : conducting zone and respiratory zone

Question 5

Summarise the function of the conducting zone

Answer 5

• no gas exchange taking place
• transfers air to and from the alveoli
• warms and humidifies inspired air
• filters and removes foreign material

Question 6

Summarise the function of the respiratory zone

Answer 6

• gas exchange
• oxygen delivery to the blood
• carbon dioxide removal from the blood

Question 7

Which structures of the respiratory system are part of the conducting zone ?

Answer 7

• trachea
• bronchi
• bronchioles
• terminal bronchioles

Question 8

Which types of cells are found in the bronchial epithelium ?

Answer 8

• ciliated cells
• goblet cells (more)
• basal cells
• clara cells (less)

Question 9

Which types of cells are found in the bronchiolar epithelium ?

Answer 9

• ciliated cells
• very very few goblet cells
• lots of clara cells

Question 10

Which types of cells are found in the alveolar epithelium ?

Answer 10

• type 1 alveolar cells
• type 2 alveolar cells
• alveolar macrophage

Question 11

Why is the conducting zone known as dead space ?

Answer 11

Because it is not involved in gas exchange

Question 12

What are the 2 types of dead space ?

Answer 12

• anatomical dead space
• physiological dead space

Question 13

Describe the function of the anatomical dead space

Answer 13

• the conducting airways that deliver air to the alveoli
• the volume is determined by the geometry of the airway network

Question 14

Describe the function of the physiological dead space

Answer 14

• volume of the lung that does not participate in gas exchange
• measured by the functional assessment of the lung

Question 15

What is the estimate for the volume of the anatomical and physiological dead space in healthy subjects ?

Answer 15

150 - 180 ml

Question 16

How are lung volumes measured ?

Answer 16

A spirometer can be used to measure changes in the volume of air in the lungs

Question 17

What is the tidal volume ?

Answer 17

It is the normal air moving in and out of the lungs (normal breathing at rest)
- 0.5 litres

Question 18

What is the inspiratory reserve volume ?

Answer 18

The amount of air that can be breathed in (maximal inhalation)
- 3.1 litres

Question 19

What is the expiratory reserve volume ?

Answer 19

• amount of air that can be breathed out (maximal exhalation)
• 1.2 litres

Question 20

What is the difference between capacity and volume ?

Answer 20

capacity is the sum of volumes that can be divided into different volumes whereas volume is a set value which cannot be subdivided

Question 21

Which values can’t be measured using spirometery ?

Answer 21

• functional residual capacity (2.4 litres)
• residual volume (1.2 litres)
• total lung capacity (6 litres)

They can’t be measured using spirometery because the air can’t be expelled

Question 22

What are the values of inspiratory capacity and vital capacity ?

Answer 22

• inspiratory capacity - 3.6 litres
• vital capacity - 4.8 litres

Question 23

What is functional residual capacity ?

Answer 23

• air remaining at the end of normal exhalation
• provides a buffer and prevents breath to breath fluctuations in alveolar gas composition
• air entering the lungs mixes with air remaining in the lungs
• 2.4 litres

Question 24

What is residual volume ?

Answer 24

• air remaining in the lungs at the end of maximal exhalation
• 1.2 litres

Question 25

What is tidal volume ?

Answer 25

Tidal volume = air in the dead space + air in the alveoli
(air entering the lungs ventilates both the dead space and the alveoli)

Question 26

What is alveolar ventilation ?

Answer 26

• It is the volume of gas entering the alveoli every minute
• alveolar ventilation = (tidal volume - dead space) x respiratory rate
• typical value at rest =4200 ml/min

Question 27

How can alveolar ventilation be increased ?

Answer 27

• increasing tidal volume
• increasing respiratory frequency

Question 28

What is the typical value of expired ventilation/minute ventilation ?

Answer 28

6000 ml/min

Question 29

What is hypoventilation ?

Answer 29

• breathing in and out too slowly compared to what the body needs
• decrease in ventilation without similar decrease in oxygen consumption or carbon dioxide production

Question 30

How can hypoventilation occur ?
(Hypercapnia)

Answer 30

• in disease states which physiological dead space
• when respiratory muscles are paralysed or the chest wall is damaged
• when tidal volume is reduced by CNS depression

Question 31

What is hyperventilation ?

Answer 31

• breathing in and out too quickly for the bodies needs
• ventilation in excess metabolic needs or carbon dioxide exhaled at a greater rate than production

Question 32

How can hyperventilation occur ?
(Hypocapnia)

Answer 32

• during acute asthma attacks
• under conditions of stress
• at altitude