Clinical Pplication Of Lung Mechanics Flashcards
What is the roles fo mucks and cilia
Dust and other particles inhaled with air • Large particles
• filtered in nose;
• deposited on mucus layer in nose, nasopharynx, swept by cilia to oropharynx
swallowed
• Medium sized particles
• Deposited on mucus lining the trachea, bronchi and larger bronchioles
• Wafted up to pharynx by cilia (muco-ciliary escalator) swallowed
• Small (1 – 5 µm)
• Carried down to alveoli
• Engulfed by macrophages removed by lymphatics and via airways (muco-ciliary)
Decisive teh histology of bronchioles
See slide
What is radial traction
Radial traction
• term used for the outward tugging action of the alveolar walls on bronchioles
• prevents collapse of bronchioles during expiration
What are compliance and elastase
Compliance - how stretchy it is
Elastance = meagre of elastic recoil - returning to original size
Compliance is proportional to 1/elastance
What is teh interstitum?
The microscopic space between the alveolar epithelium and capillary endothelium
What does the interstitial contain?
Interstitium contains:
• elastin fibres,
• collagen fibres
• fibroblasts
What is interstitial lung disease (diffuse lung fibrosis)?
Fibrous tissue in the interstitium • Lungs are stiff so harder to expand • lung compliance is lower
• Elastic recoil of the lungs is increased
• The lung volume is lower than normal
• 0Restrictive’ type of ventilatory defect
What causes interstitial lung disease
Can follow
• a specific exposure - e.g., asbestos, drugs, mouldy hay etc
• autoimmune-mediated inflammation
• Unknown injury (e.g., idiopathic pulmonary fibrosis)
- If the exposure or injury persists or if the injury repair process is imperfect, the lung may be permanently damaged
- with increased interstitial tissue replacing the normal capillaries, alveoli, and healthy interstitium.
What is functional residual capacity
FRC = Functional residual capacity
The volume of air in the lungs at the end of a quiet expiration
What are the symptoms of interstitial lung diesease
Symptoms • Breathlessness • Dry cough • Relevant previous history: occupation, drug history, etc Signs Chest expansion is ???
What happens to gas exchange in interstitial lung disease
In the normal lung: air in alveoli lies as close as 0.2μm from blood streaming through capillaries.
2 2
In interstitial lung disease (diffuse lung fibrosis) • alveolar capillary membrane is thickened • Increases diffusion distance for O • Impairs gas exchange (more next week)
and CO
(Diffusion defect)
What is emphysema
Definition:
• Abnormal, permanent enlargement of the air spaces distal to the terminal bronchiole
• With destruction of alveolar walls
(No fibrosis)
Protease mediated destruction of elastin is an important feature
Reduced elasticity is a key problem
Large air spaces -> reduced surface area for gas exchange
What can cause emphysema?
Due to
• Smoking and inhaled pollutants, (COPD is commonest cause)
cause inflammatory cells to accumulate; which release elastases and oxidants -> destroy alveolar walls and elastin
• Most have chronic bronchitis concurrently (since smoking is a risk factor for both).
What is COPD
Chronic Obstructive Pulmonary disease (COPD) = umbrella term including both
Emphysema + chronic bronchitis
Larger airways - chronic bronchitis
Smaller airways and alveoli - emphysema .
Most ppl with emphysema have chronic bronchitis too
Where is chronic bronchitis usually sen
- Chronic bronchitis is seen in the larger airways
- Mucus hypersecretion (from goblet cells & sub mucous glands)
- Reduced cilia – mucus is not cleared effectively
Why is airway obstriction worse in expiration than inspiration
Inspiration 0 negative pressure in pleural space during inspiration helps to keep he lower airways open
Positive intra pulmonary pressure during expiration exacerbates narrowing of intrathoracic airways
Describe the chanegs in emphysema
- Loss of elastic tissue
- Elastic recoil is decreased.
- Compliance increased
- Small airways collapse in expiration (loss of radial traction)
- Air trapping (due to airway obstruction and low elastic recoil )
- Hyper inflated: Barrel chest
- obstructive pattern on spirometry testing
What is a barrel chest
Normal: ratio of Antero-posterior : lateral diameter = 1:2
Barrel chest: Antero-posterior : lateral diameter = 1:1
Compare the X-rays of normal lungs and emphysema
Normal inflation vs hyper inflation
Normal - diaphragm crosses 5th rib anteriorly
Emphysema - diaphragm crosses 8th rib anteriorl, diaphragm flattened
See slide
How does pneumothorax occur
• If the chest wall or the lung is breached,
• A communication is created between pleural space and atmosphere
• Air flows from atmosphere (higher pressure) -> into the pleural cavity (lower pressure)
• Until the pleural pressure = atmospheric pressure
• The pleural seal is lost
• Lung elastic recoil not counter-balanced by negative pleural pressure
• Lung collapses to unstretched size
Chest drain with underwater seal used
What is atelectasis
Atelectasis (lung collapse) Inadequate expansion of air spaces
• In new-born babies: failure of alveoli to expand at birth
• Compression collapse: due to
• air in pleural cavity (pneumothorax)
• fluid in the pleural cavity (pleural effusion)
• Resorption collapse: due to obstruction
Airway obstructed; air downstream of
blockage slowly absorbed into blood stream
What is resorption collapse
Collapse due to obstruction of a large airway (eg Lung cancer, mucus plugs)
What is neonatal respiratory distress syndrome
Surfactant
• Produced by Type II alveolar cells; starts at 24 – 28 weeks gestation;
• increasing amounts by 32 weeks
• Usually sufficient by 35 – 36 weeks
In preterm babies Insufficient surfactant -> high surface tension lung expansion at birth is incomplete; some alveoli remain collapsed (airless); no gas exchange occurs in these alveoli
The lung is stiff Increased effort is required to breathe – respiratory difficulty Results in impaired ventilation
What are some features of respirate difficulty from birth and what are some treatments
In preterm babies (severe < 30 weeks) • Features of respiratory difficulty from birth • grunting, • nasal flaring, • intercostal and subcostal retractions • Rapid respiratory rate (tachypnea) • cyanosis
- Treatment includes
- surfactant replacement via an endotracheal tube,
- supportive treatment with oxygen and assisted ventilation
