Clinical application of lung ventilation Flashcards
Outline how ventilation takes place
- Inspiratory muscles contract
- Chest expands, taking lung with it (pleural seal)
- Air flows in, overcoming airways resistance
What do the lungs need to do in order to expand?
- Overcome elastic properties of alveolar walls
- Overcome surface tension of fluid
What is quiet expiration?
- Passive process
- Needs elastic recoil of lungs
- Need to overcome airways resistance
What is COPD?
- 3rd leading cause of death worldwide
- Primarily caused by smoking and/or inhaled pollutants with genetic vulnerability
- Clinical syndrome characterised by chronic respiratory symptoms with associated pulmonary abnormalities
- All conditions share impaired airflow that is not fully reversible
Why is COPD greatly underdiagnosed?
- COPD may start in people in their 30s though typical age of presentation is in the 60s
- Should be recognised earlier
- Earlier intervention slows lung function decline
Which 2 lung conditions often exist in COPD?
- Chronic bronchitis and emphysema
What does emphysema affect?
- affects spaces distal to terminal bronchiole
Where does chronic bronchitis affect the lungs?
- Seen in larger airways
- Results in mucus hypersecretion from goblet cells and sub-mucous glands
- Reduced cilia - mucociliary escalator function impaired
Compare cartilage in small bronchi vs bronchioles
- Small bronchi have small islands of cartilage
- Bronchioles have no cartilage
Compare glands in small bronchi vs bronchioles
- Small bronchi have glands in the submucosa
- Bronchioles have no glands
What keeps the lumens of the bronchioles open?
- No cartilage
- Radial traction (outward tugging) of surrounding alveolar walls on bronchioles
- Prevents collapse of bronchioles during expiration
What is the definition of emphysema?
- Abnormal, permanent enlargement of air spaces distal to terminal bronchiole
- With destruction of alveolar walls
- No fibrosis
Outline the pathophysiology of emphysema
- Protease mediated destruction of elastin
- Loss of elastic tissue
- Compliance increased (more easily stretched)
- Elastic recoil reduced (lung remains more expanded at end of expiration)
- Damaged alveolar walls leads to loss of radial traction
- Bronchioles collapse in expiration
- Air trapping due to airway obstruction and decreased elastic recoil
What signs can be seen in a patient who is suffering from air trapping due to emphysema?
- Hyper inflated: barrel chest
- Obstructive pattern on spirometry
What happens to the bronchioles in COPD?
- Walls of bronchioles and bronchi become inflamed and plugged with mucus
- Airway resistance is increased
How can you tell that someone has a barrel chest?
- Antero-posterior: lateral diameter diameter = 1:1
How can you see hyperinflation on a chest X-ray?
- Diaphragm crosses 8th rib anteriorly and is flattened
- In a normal lung, diaphragm crosses 5th rib anteriorly
What is the interstitium of the lungs?
- Microscopic space between alveolar epithelium and capillary endothelium
- Gas exchange occurs across interstitial layer
- If it is damaged, gas exchange is impaired
What does the interstitium contain?
- Elastin fibres
- Collagen fibres
- Fibroblasts
- Matrix substance
What happens to the interstitium in pulmonary fibrosis?
- Interstitium is thickened and fibrosed
What are some occupational interstitial lung diseases?
- Asbestosis
- Silicosis
- Coal worker’s pneumoconiosis
What are some connective tissue diseases that cause interstitial lung disease?
- Rheumatoid arthritis
What are some immunological causes of interstitial lung diseases?
- Sarcoidosis
- Ext. allergic alveolitis
What are some immunological causes of interstitial lung disease?
- Fibrosing alveolitis
What is the pathophysiology of interstitial fibrosis?
- If exposure or injury persists or if repair process is imperfect, permanent damage may occur
- Increased interstitial tissue replacing normal capillaries, alveoli, and healthy interstitium
What is the effect of fibrosis on the lungs?
- Lung compliance is reduced - lungs are stiff; harder to expand
- Elastic recoil of lungs is increased - resting lung volume is smaller than normal
- Restrictive type of ventilatory defect on spirometry
What happens to gas exchange in diffuse lung fibrosis?
- Alveolar capillary membrane is thickened
- Increases diffusion distance for O2 and CO2
- Impairs gas exchange
What are the symptoms of lung fibrosis?
- Breathlessness on exertion/at rest
- Dry cough
- Relevant previous history e.g. occupation, drug history, etc.
What are the signs of lung fibrosis?
- Chest expansion is reduced
What is the tidal volume?
- Volume of air that enters and leaves lungs with each breath
How do we further increase lung volume?
- Increase lung volume to extent of inspiratory reserve volume
- During normal quiet respiration, increase in lung volume is not maximal
How do we breathe out more than at rest?
- Use expiratory reserve volume
Can we completely empty our lungs?
- No
- Even after forced expiration a residual volume of air remains
What are the fixed points that lung capacities are defined relative to?
- Maximum inspiration
- Maximum expiration
- The end of a quiet expiration
What is vital capacity?
- Inspiratory reserve volume + tidal volume + expiratory reserve volume
What is total lung capacity?
- Vital capacity + residual volume
What is functional residual capacity?
- Volume of air in lungs at the end of quiet expiration
- Expiratory reserve volume + residual volume
What functional residual capacity depend on?
- Balance between lung elastic recoil and chest wall elastic wall recoil
- Emphysema leads to increased FRC
- Lung fibrosis leads to reduced FRC
What causes neonatal respiratory distress syndrome?
- Pre-term babies <35 weeks don’t produce sufficient lung surfactant
- High surface tension
- Lung expansion at birth incomplete
- Some alveoli remain collapsed and no gas exchange can occur
- Lung is stiff
- Increased effort required to breathe - babies grunt + nasal flaring
- Results in impaired ventilation
What are the clinical features of NRDS?
- Grunting
- Nasal flaring
- Intercostal and subcostal retractions
- Tachypnoea
- Cyanosis
How is NRDS treated?
- Surfactant replacement via endotracheal tube
- Supportive treatment with oxygen and assisted ventilation
What is a pneumothorax?
- Pleural seal is lost
- Lung elastic recoil not counter-balanced by negative pleural pressure
- Air rushes in, causing lung to collapse
- Compression collapse
What is the balance of forces at the end of quiet expiration?
- Chest wall always wants to move outwards and lungs always want to move inwards
What happens to the balance of forces during a pneumothorax?
- Chest wall or lung is breached
- Communication is created between pleural space and atmosphere
- Intrapleural pressure increases and allows lung to collapse
What is a resorption collapse?
- Collapse due to obstruction of a large airway
What is atelectasis?
- Alveoli not ventilated so can’t participate in gas exchange
- Collapsed alveoli more susceptible to lung infection including pneumonia
- Common post-operative complication
- Prevent with good pain control to enable coughing/clearance of mucus, deep breathing exercises, early ambulation
What affects the brainstem to cause hypoventilation?
- Opiates
- Head injury
What affects the spinal cord to cause hypoventilation?
- Trauma
What affects the phrenic and intercostal nerves to cause hypoventilation?
- Guillain-Barre syndrome
What affects the neuromuscular junction to cause hypoventilation?
- Myasthenia gravis
What affects the muscles of respiration to cause hypoventilation?
- Inherited muscle diseases e.g. Duchenne muscular dystrophy
What affects the chest wall to cause hypoventilation?
- Severe obesity
- Kyphoscoliosis
- Flail segment
What affects the pleural cavity to cause hypoventilation?
- Pneumothorax
- Large pleural effusions
What affects lung compliance to cause hypoventilation?
- Respiratory distress of newborn
- Lung fibrosis in interstitial lung disease
What affects the upper airway to cause hypoventilation?
- Obstruction due to laryngeal oedema or foreign body
What affects airway resistance to cause hypoventilation?
- High airway resistance due to very severe acute asthma or late stages of COPD
What affects airway resistance to cause hypoventilation?
- High airway resistance due to very severe acute asthma or late stages of COPD
