Session 2: Some Disorders of Ventilation and Lung Mechanics

Question 1

Give some common disorders of ventilation and lung mechanics.

Answer 1

Interstitial lung disease

Respiratory distress syndrome in the new born

Emphysema

Asthma

Pneumothorax

Hypoventilation

Question 2

Explain the relationship between compliance and elastic recoil.

Answer 2

It’s an inverse relationship.

Question 3

Bronchioles have no cartilage. How do they stay open in expiration?

Answer 3

Due to something called radial traction.

This is the outward tugging actiong of the surrounding alveolar walls on bronchioles.

Question 4

Briefly explain what interstitial lung disease is.

Also give the cause.

Answer 4

This is the thickening of the pulmonary interstitium. A lot of collagen is layed down in the interstitium.

There are over 200 different types of the disease and causes.

However the common final pathway almost always result in the same thing: lung fibrosis.

Question 5

Is interstitial lung disease reversible?

Answer 5

Sometimes, sometimes not.

It depends on what kind and how early it was detected/treated.

Question 6

Give a some common causes of interstitial lung disease.

Answer 6

Asbestos

Coal workers pneumoconiosis

Radiation

Rheumatoid arthritis

Sarcoidosis

Exterernal alleric alveolitis

Fibrosing alveolitis

Question 7

Which lung is healthy?

Answer 7

The left lung.

Question 8

What does pulmonary interstitium contain?

Answer 8

Elastin fibres

Collagen fibres

Fibroblasts

Matrix substance

In interstitial lung disease there is a lot more collagen fibres.

Question 9

Explain the pathophysiology of interstitial lung disease.

(Consequences of the disease)

Answer 9

The lungs become stiffer and harder to expand since the collagen fibres are less stretchy than elastin fibres.

Lung compliance is reduced.

Elastic recoil of the lungs is increased.

Smaller lungs

On examination chest expansion is reduced.

Also thicking of the alveolar walls increases the distance oxygen has to diffuse from alveolar air to the blood and vice versa. Less efficient gas exchange.

Question 10

Why are the lungs smaller in interstitial lung disease?

Answer 10

Because of the increased elastic recoil creating a netforce inwards since the chest recoil of the muscles still stay the same.

Question 11

Symptoms of interstitial lung disease.

Answer 11

Shortness of breath

Reduced exercise tolerance

Dry cough

Fatigue

Question 12

Signs of interstitial lung disease.

Answer 12

Tachypnoea

Tachycardia

Reduced chest movement (bilaterally)

Coarse crackles

Pleural effusions

Finger clubbing

Question 13

How can you examine the reduced chest movement of interstitial lung disease.

Answer 13

If you put your hands on their back with your thumbs touching. In a normal lung as they take a deep breath your thumbs should separate.

If they don’t, this is a sign.

Question 14

What happens to compliance in interstitial lung disease?

Answer 14

It is greatly reduced.

Question 15

Explain Respiratory distress syndrome in new born.

Answer 15

It comes down to insufficient amount of surfactant.

Surfactant is produced by type II pneumocytes in increasing quantities from 32 weeks’ gestation.

RDS is therefore caused by deficiency of surfactant in premature babies, particularly those less than 30 weeks old.

Question 16

Pathophysiology of RDS in new born.

Answer 16

Without the surfactant the surface tension in the fluid lining of the alveoli will be high.

This makes the lungs harder to expand at birth. Since lung expansion is incomplete and due to the absence of surfactant some alveoi remain collapsed and some existing ones start to collapse. There is no gas exchange in these alveoli.

Lungs are stiffer and harder to expand which means compliance is low.

This means more effort is needed to breathe sufficiently.

Impaired ventilation.

Question 17

Signs of RDS in new born.

Answer 17

Cyanosis

Grunting

Intercostal and subcostal recession.

Nasal flaring

Tachypnoea

Question 18

Treatment of RDS of the new born.

Answer 18

Surfactant replacement via an endotracheal tube

Supportive treatment with oxygen and assisted ventilation.

Question 19

Classic definition of COPD encompasses two medical conditions.

Which?

Answer 19

Chronic bronchitis

Emphysema

Question 20

Which part of the airways/lungs is affected in COPD?

Answer 20

From bronchi to bronchioles.

Question 21

Pathophysiology of chronic bronchitis.

Answer 21

There is mucus hypersecretion from goblet cells and submucus glands.

There is also reduced cilia which means that the mucus is not cleared effectively and can lead to mutliple infections.

Airflow is limited and obstructed.

Epithelial remodeling.

Parts of airways tend to collapse because of increased surface tension.

Question 22

Clinical diagnosis of chronic bronchitis.

Answer 22

Cough productive sputum over three months of the year for over one year.

Question 23

Common cause of emphysema (and COPD).

Answer 23

90% of cases of COPD and emphysema are due to smoking.

Inhaled cigarette smoke results in the breakdown of elastin fibres and alveolar walls.

Question 24

Pathophysiology of emphysema.

Answer 24

Loss of elastin fibres due to the cigarette smoke.

Higher compliance since there is less elastin and less elatic recoil.

The reduction of elastic recoil disturbs the net balance between elastic recoil (inwards) and chest recoil (outwards).

This causes the lungs to be hyperinflated.

The small airways are narrowed.

Question 25

Why are the small airways narrowed?

Answer 25

Due to the loss of elastic fibres which exert an outwards pull (the radial traction) on the small bronchioles.

Radial traction is reduced and this increases airways resistance.

Question 26

Signs of emphysema.

Answer 26

Barrel chest due to the hyperinflation.

Question 27

How is the airways resistance increased in chronic bronchitis?

Answer 27

Increased mucus production in bronchitis ‘fills’ the bronchi causing obstruction.

Question 28

Symptoms of emphysema.

Answer 28

Shortness of breath and reduced exercise tolerance.

Question 29

Causes of emphysema not due to smoking.

Answer 29

Alpha-1 antitrypsin deficiency which is inherited.

Alpha-1 antitrypsin is an anti-proteinase.

If alpha-1 antitrypsin is not produced this leads to an imblanace in proteinases and antiproteinases. This leads to destruction of elastin in early age and signs usually show early on as well.

Question 30

What is asthma?

What triggers it?

Answer 30

A chronic inflammatory process.

May be triggered in susceptible individuals by allergic and/or non-allergic stimuli.

Question 31

Pathophysiology of asthma.

Answer 31

The inflammation leads to airway narrowing due to bronchial smooth muscle contraction.

There is also thickening of airways walls by mucosal oedema and excess mucus production which can partially block the lumen.

All of this greatly increases airway resistance. This makes it much harder to inspire.

Question 32

What is a pneumothorax?

Answer 32

The presence of air in the pleural space.

Question 33

Explain how a pneumothorax can come about, and why.

Answer 33

The intrapleural pressure is always less than the atmospheric pressure.

This intrapleural pressure along with the pleural seal makes the visceral pleura of the lungs stick to the chest wall (parietal pleura.

However if an opening is created which means that the pleural space can communicate with the outside. This will cause air to quickly flow into the pleural cavity down the pressure gradient until equilibrium is reached (intrapleural pressure = atmospheric pressure).

This causes the pleural seal to be broken and the elastic recoil of the lung is not affected by the chest wall recoil anymore. The lung will collapse towards its hilum.

Question 34

Give some causes of pneumothorax.

Answer 34

Trauma to chest like a stab.

Spontaneous rupture of a weak area of the lung.

Insertion of central venous catheter via the subclavian vein (higher incidence) or the internal jugular vein (lower incidence).

Question 35

Is pneumothorax simply a collapsed lung?

Answer 35

No, lung collapse is not synonymous with pneumothorax because there are other causes of lung collapse.

Question 36

Fancier word for lung collapse.

Answer 36

Atelectasis

Question 37

Briefly explain atelectasis.

Answer 37

Incomplete expansion of the lungs or collapse of previously inflated lung.

This produces areas of relatively airless pulmonary parenchyma.

Question 38

Main types of atelectasis.

Answer 38

Neonatal atelectasis

Compression atelectasis

Resportion atelectasis.

Question 39

What is compression atelectasis?

Answer 39

Whenever significant volumes of air or fluid accumulate in the pleural cavity.

Question 40

Common causes of compression atelectasis.

Answer 40

Pneumothorax or pleural effusion.

Question 41

What is resorption atelectasis?

Answer 41

Complete obstruction of airways which means that over time air is resorbed from the alveoli and they will collapse.

Question 42

Causes of resorption atelectasis.

Answer 42

Bronchial carcinoma

Excessive mucuous secretion and failure of clearance. (Can happen after surgery with an inability to cough, cystic fibrosis, severe asthma attacks)

Foreign body (common in children which inhale something)

Question 43

Causes of hypoventilation.

Answer 43

Incorrect neural output. Impulses originating in the respiratory centre needs to reach the respiratory muscles via spinal pathways and nerves.

Malformed bony thorax

Respiratory muscles weakness of any cause

Severe thoracic wall deformities

Very stiff lungs (high compliance)

Severe airway obstructions.