Lecture 3: Clinical application in ventilation and lung mechanics

Question 1

What is interstitial lung disease?

Answer 1

Umbrella term used for a large group of heterogenous diseases characterised by:

• alveolar septal (interstitium) thickening
• fibroblast proliferation
• collagen deposition
• pulmonary fibrosis: if process remains unchecked

e.g. Diffuse lung fibrosis: characterised by stiffer lungs with reduced volume

Question 2

What is the interstitial space?

Answer 2

Potential space b/w alveolar cells and capillary basement membrane
It is only apparent in disease states when it may contain fibrous tissue/cells/fluid

Question 3

Give some examples of types of interstitial lung disease:

Answer 3

Asbestosis: caused by asbestos exposure
Pneumoconiosis: general term for a class of interstitial lung disease where inhalation of dust has cause interstitial fibrosis e.g. coal miners lung
Untreated hypersensitivity pneumonitis: immunologically mediated lung disease caused by repeptitive inhalation of antigens (usually residential areas)

Question 4

What effects does the deposition of fibrous tissue in the interstitium have?

Answer 4

• lungs are stiffer and harder to expand, since the collagen fibres are less stretchy than the elastin fibres, so lung compliance is reduced
• elastic recoil is increased (tendancy of both collagen and elastin fibres to return to original size), so therefore lungs are smaller due to increased elastic recoil
• causes restrictive type of ventilatory defect in spirometry
• on examination, chest expansion is reduced
• residual volume, funcitonal reserve capacity, vital capacity, total lung capacity, as measured by spirometry are reduced
• diffusion capacity is also reduced
• thickening of alveolar walls increases the distance gases have to diffuse from air to blood (effect on diffusion of oxygen is greater than CO2, as CO2 is more soluble)

Question 5

Are the airways narrowed in interstitial lung disease?

Answer 5

No, the fibrous tissue exerts and outward pull (radial traction) on small bronchioles, keeping airways open.

Question 6

What are some symptoms and signs of interstitial lung disease?

Answer 6

Symptoms:
-reduced exercise tolerance with dyspnoea (laboured breathing) on exertion and a dry cough
-as disease progresses, shortness of breath at rest develops
-malaise and fatigue
Signs:
-tachypnoea (increased resp rate)
-tachycardia
-reduced chest movement bilaterally
-fine crackles

Question 7

What may ‘poor inspiratory effort’ on a chest X-Ray mean?

Answer 7

Could be because patient didn’t understand instructions to take a deep breath in, too aceutly unwell to take deep breath, or tired
However it could be due to a restrictive lung disease
-if patients X-Rays keep coming back ‘poor’ this shoudl be investigated

Question 8

What is idiopathic lung fibrosis?

Answer 8

No cause identified

Question 9

What are some occupational interstitial lung diseases?

Answer 9

• asbestosis
• coal workers pneumoconiosis
• silicosis (inhalation of crystalline silica dust)

Question 10

What are some treatment related interstitial lung diseases?

Answer 10

• radiation
• methotrexate
• chemotherapy
• amiodarone
• methotrexate

Question 11

What are some connective tissue interstitial lung diseases?

Answer 11

• rh. arthritis

- schleroderma

Question 12

What are some immunological interstitial lung diseases?

Answer 12

• sarcoidosis

- ext. allergic alveolitis

Question 13

What is respiratory stress syndrome in a new born?

Answer 13

Results in stiff lungs (reduced compliance)

• surfactant is produced by type 2 pneumocytes in increasing quantities from 32 weeks
• RDS is caused by deficiency in surfactant in prem babies
• without surfactant, ST is high
• harder for lungs to expand at birth, lung expansion is incomplete and some alveoli remain collapsed (no gas exchange in collapsed alveoli)
• lung compliance is low
• increased effort required to breath
• results in impaired ventilation

Babies have sings of respiratory distress: cyanosis, grunting, intercostal and subcostal recession

Question 14

How do you treat RDS?

Answer 14

Surfactant replacement via endotracheal tube, and supportive treatment with oxygen and assisted ventilation

Question 15

What is emphysema?

Answer 15

Loss of elastin and breakdown of alveolar walls, causing increased lung compliance, decreased elastic recoil, narrowing of small airways (irreversible) , loss of alveolar SA

Question 16

What is emphysema a feature of?

Answer 16

COPD
90% of COPD cases are caused from smoking, the host response to cigarette smoke results in the brekadown of elastin fibres and alveolar walls

Question 17

What does loss of elastin fibres in emphysema cause?

Answer 17

• lungs easier to expand as there is less elastin (lung compliance increased)
• elastic recoil of lung is reduced
• at rest the lungs are hyperinflated, due to loss of recoil
• on examination hyperinflation cuases appearance of barrel chest
• small airways are narrowed due to loss of elastic fibres exterting an outward pull (radial traction) on small bronchioles
• airway narrowing causes an obstructive type of ventilatory defect on spirometry

Question 18

What are the symptoms of emphysema?

Answer 18

• shortness of breath
• reduced exercise tolerance
• cough

Question 19

What is a rarer cause of emphysema?

Answer 19

Alpha-1 antitrypsin deficiency

• inherited
• alpha-1 antitrypsin is an antiproteinase, so its deficiency leads to an imbalance of proteinases and antiproteinases
• this leads to the destruction of elastin
• presents at an early age

Question 20

What is asthma?

Answer 20

Reversible airway construction

• chronic inflammatory process, which may be triggered by allergic/non-allergic stimuli
• inflammation causes airway narrowing due to bronchial smooth muscle contraction, thickening of airway walls by mucosal oedema, excess mucus production which can partially block the lumen

Question 21

What is a pneumothorax?

Answer 21

A disorder where air enters the pleural space, with loss of pleural seal and lung collapse

Question 22

How does a pneumothorax occur?

Answer 22

• at rest the intra-pleural pressure is slightly below atmospheric pressure and the ST of pleural fluid creates a seal which keeps lung adherent to chest wall
• if an opening is created allowing the pleural cavity to communicate with the outside, air will flow into pleural cavity down pressure gradient until the pressure in the pleural cavity matches the atmospheric pressure
• pleural seal is broken so elastic recoil of the lung causes it to collapse towards to hilum

Question 23

What is atelectasis?

Answer 23

Incomplete expansion of the lungs (neonatal atelectasis) OR the collapse of a previously infalted lung

Question 24

What are the main types of acquired pulmonary atelectasis in adults?

Answer 24

Compression atelectasis:
-whenever significant volumes of air (pneumothorax) or fluid (pleural effusion) accumulate within the pleural cavity and compress small airways
Resorption atelectasis:
-stems from complete obstruction of an airway, over time air is resorbed from the alveoli, which collapse

Question 25

When the term lung collapse is used on its own, what condition is it usually referring to?

Answer 25

Resorption atelectasis secondary to airway obstructione.g. due to tumour, muscous secretions

Question 26

What is hypoventilation?

Answer 26

Due to poor expansion of the thoracic cavity or lungs

• normal ventilation requires expansion of thoracic cavity and lungs, which requires impulses from the respiratory centres in the CNS to reach the respiratory muscles via spinal pathways and nerves
• efficient chest expansion also requires a bony thorax

Respiratory muscle weakness/severe thoracic wall deformities can cause hypoventilation and respiratory failure
-very stiff lungs/severe airway obstruction can also cause hypoventilation

Question 27

What is the defining feature of hypoventilation?

Answer 27

Hypercapnia: high CO2

Question 28

Where is the most common setting in which atelectasis occurs?

Answer 28

Post-operatively (typically develpoing within 24hrs of surgical intervention)

Question 29

What are the risk factors of post-operative atelectasus?

Answer 29

• increasing age
• underlying lung disease
• obesity
• general anaesthesia
• chest/abdominal surgery
• poor post-operative pain control leading to a supressed cough and shallow breathing

Question 30

What causes the intrapleural pressure to be less than the atmospheric pressure?

Answer 30

The thin film of pleural fluid (pleural seal), is pulled in opposite directions resulting in a vacuum effect, causing the intrapleural pressure to be less than atmospheric pressure

Question 31

How are inhaled particles of dust removed from the respiratory tract?

Answer 31

Cilia trap the inhaled particles and the mucociliary escalator wafts mucus and particles up to be swallowed and destroyed in stomach
-in miners some particles reach the alveoli,the macrophages destory this, but release elastase which destroys elastin = coal miners lung

Question 32

What would you expect an X-Ray of a person with emphysema to look like?

Answer 32

• larger black area due to increased volume of air
• lungs hyperinflated
• diaphragm flattened

Question 33

What are the axis on a compliance curve?

Answer 33

X axis- pressure

Y axis- volume