Lec 2 - Ventilation and Lung mechanics

Question 1

What are some disorders that present as quiet expiration?

Answer 1

Emphysema –> This is the destruction of elastic fibres leading to a decrease in the elastic recoil of the lungs.

Asthma and COPD –> The increases airways resistance.

Question 2

What are some disorders that present as difficulty in lung expansion?

Answer 2

Diffuse lung fibrosis –> increased collagen in alveolar walls, makes the lungs stiff.

Respiratory distress in the newborn –> This is due to decreased surfactant leading to increased surface tension.

Question 3

What is a brief description of pneumothorax?

Answer 3

Pleural seal lost and lung collapsed.

Question 4

What is a brief description of Hypoventilation?

Answer 4

Inspiratory muscles not working.

Question 5

What are parts of the conducting portion in the respiratory tract?

Answer 5

• Nasal Cavity
• Pharynx
• Larynx
• Trachea
• Primary bronchi
• Secondary bronchi
• Bronchioles
• Terminal bronchioles

Question 6

What are parts of the respiratory portion of the respiratory tract?

Answer 6

• Respiratory bronchioles
• Alveolar ducts
• Alveoli

Question 7

What is the epithelium for the conducting portion excluding the bronchioles and terminal bronchioles?

Answer 7

Pseudostratified epithelium with cilia and goblet cells.

-This lines the airways from the nasal cavity to the largest bronchioles.

Question 8

What is the epithelium for the bronchioles and terminal bronchioles?

Answer 8

-Simple columnar epithelium with cilia and Clara cells but no goblet cells.

Question 9

What is the epithelium for the respiratory portion excluding the alveoli?

Answer 9

-Simple cuboidal epithelium with a few sparsely scattered cilia and Clara cells.

Question 10

What is the epithelium for the alveoli?

Answer 10

-Simple squamous/ type 1

Question 11

What is the role of mucus and cilia on the inhalation of large particles?

Answer 11

• They are filtered in the nose.
• They are then deposited on the mucus layer in the nose, nasopharynx and swept by cilia to the oropharynx before they are swallowed.

Question 12

What is the role of mucus and cilia on the inhalation of medium sized particles?

Answer 12

• They are deposited on mucus lining the trachea, bronchi and larger bronchioles.
• They are then wafted up to the pharynx by cilia (muco-ciliary escalator) and then they are swallowed.

Question 13

What is the role of mucus and cilia on the inhalation of Small particles?

Answer 13

• They are carried down to alveoli.

- They are engulfed by macrophages and then removed by lymphatics and via airways (muco-ciliary)

Question 14

What do pulmonary and bronchial arteries carry?

Answer 14

• pulmonary arteries carry deoxygenated blood.

- bronchial arteries carry oxygenated blood.

Question 15

What is radial traction?

Answer 15

It is the outward tugging action of the alveolar walls on the bronchioles.
– This prevents the collapse of the bronchioles during expiration.

Question 16

What do type I and type II alveolar cells do?

Answer 16

Type I –> these permit gas exchange.

Type II –> These secrete surfactant.

Question 17

What is compliance?

Answer 17

Compliance is a measure of how stretchy the lung is.

Question 18

What is elastance?

Answer 18

Elastance is a measure of elastic recoil.

– It is the tendency to return to their original shape when stretched.

Question 19

Relate compliance to elastance?

Answer 19

Compliance is directly proportional to 1/elastance.

• When compliance increases, elastic recoil decreases.
• When compliance decreases, elastic recoil increases.

Question 20

What is the interstitium and what does it contain?

Answer 20

it is the microscopic space between the alveolar epithelium and capillary endothelium.

Contains:

• elastin fibres
• collagen fibres
• fibroblasts

Question 21

What can lead to interstitial lung fibrosis?

Answer 21

1. a specific exposure such as asbestos, drugs and mouldy hay etc.
2. autoimmune mediated inflammation.
3. Unknown injury such as idiopathic pulmonary fibrosis.

Question 22

Describe the mechanisms of pulmonary fibrosis?

Answer 22

-Overall the function residual capacity is decreased.

• There is fibrous tissue in the interstitium.
  1. The lungs are stiff, therefore are harder to expand.
  2. The lung compliance is low.
  3. elastic recoil of the lungs is high.
  4. The lung volume is lower than normal.
  5. The airways are not obstructed.
  6. Restrictive type of ventilatory defect.
  7. There is a restrictive pattern on the spirometry testing.

Question 23

What are the signs and symptoms of pulmonary fibrosis?

Answer 23

breathlessness
dry cough
relevant previous history such as occupation and drug history etc.

signs are: chest expansion is reduced bilaterally.

Question 24

Describe the pathology of interstitial lung disease (diffuse lung fibrosis)?

Answer 24

1. The alveolar capillary membrane is thickened.
2. this increases diffusion distance for oxygen and carbon dioxide.
3. This impairs gas exchange.

Question 25

What is emphysema?

Answer 25

- It is the abnormal, permanent enlargement of the air spaces distal to the terminal bronchiole. - This is done by the destruction of the alveolar wall. - There is no fibrosis. - protease mediated destruction of elastin is an important feature. - There is the reduced elasticity. - The large air spaces mean that there is a reduced surface area for gas exchange.

Question 26

What are the causes of emphysema?

Answer 26

1. smoking and inhaled pollutants --> This causes inflammatory cells to accumulate, which releases elastase and oxidants, which destroy alveolar walls and elastin. 2. Most have Chronic bronchitis concurrently. 3. Chronic obstructive pulmonary disease (COPD) for example emphysema and bronchitis. 4. Chronic bronchitis is seen in the larger airways - --> you get mucus hyper secretion from goblet cells and sub mucous glands - --> Mucus is also not cleared effectively due to the reduced cilia.

Question 27

Why is airway obstruction worse in expiration than inspiration?

Answer 27

- In inspiration there is negative pressure in the pleural space during inspiration, which helps to keep the lower airways open. - In expiration, there is a positive intrapulmonary pressure during expiration, which exacerbates the narrowing of the intra thoracic airways.

Question 28

Describe the mechanism of emphysema.

Answer 28

- There is the loss of elastic tissue, so elastic recoil is decreased. - This means that compliance is increased. - Small airways collapse in expiration due to the loss of radial traction. - There is the trapping of air due to airway obstruction and reduced elastic recoil. - You can get hyper inflation known as barrel chest. - You also see an obstructive pattern on spirometry testing.

Question 29

What is barrel chest?

Answer 29

It is the increase in the anterior posterior diameter of the chest wall. -The lungs are chronically overinflated with air so the ribcage stays partially expanded at all time.

Question 30

Describe the mechanism of a pneumothorax.

Answer 30

1. If the chest wall or the lung is breached (stabbing), a communication is created between pleural space and atmosphere. 2. Air flows from the atmosphere into the pleural cavity from a higher pressure to a lower pressure. - - This is until the pleural pressure is equal to atmospheric pressure. 3. The pleural seal is lost. 4. Lung elastic recoil is not counter-balanced by negative pleural pressure so the lung collapses to unstretched size.

Question 31

When does Atelectasis (lung collapse) occur?

Answer 31

1. In new-born babies --> there is the failure of alveoli to expand at birth due to lack of surfactant. 2. Compression collapse due to: - ->air in pleural cavity --> pneumothorax. - -> Fluid in the pleural cavity --> pleural effusion. 3. Resorption collapse due to obstruction --> if the airway is obstructed, the air downstream of blockage is slowly absorbed into the blood stream.

Question 32

What is resorption collapse?

Answer 32

-This is the collapse due to obstruction of a large airway due to things such as lung cancer and mucus plugs.

Question 33

What is surfactant produced by and when?

Answer 33

- Produced by Type II alveolar cells. - production starts at 24-28 weeks gestation. - Increasing amounts by 32 weeks. - usually sufficient by 35-36 weeks.

Question 34

What is surfactant like in preterm babies?

Answer 34

- There is insufficient surfactant, which results in high surface tension. - As a result lung expansion at birth is incomplete. - So some alveoli remain collapsed (airless), so there is no gas exchange here.

Question 35

What are some features of respiratory difficulty from birth?

Answer 35

- grunting - nasal flaring - intercostal and subcostal retractions - rapid respiratory rate (tachypnea) - cyanosis

Question 36

What are treatments for respiratory difficulty?

Answer 36

- surfactant replacement via an endotracheal tube. | - supportive treatment with oxygen and assisted ventilation.