Lecture 3: Clinical application in ventilation and lung mechanics Flashcards
What is interstitial lung disease?
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
What is the interstitial space?
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
Give some examples of types of interstitial lung disease:
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)
What effects does the deposition of fibrous tissue in the interstitium have?
- 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)
Are the airways narrowed in interstitial lung disease?
No, the fibrous tissue exerts and outward pull (radial traction) on small bronchioles, keeping airways open.
What are some symptoms and signs of interstitial lung disease?
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
What may ‘poor inspiratory effort’ on a chest X-Ray mean?
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
What is idiopathic lung fibrosis?
No cause identified
What are some occupational interstitial lung diseases?
- asbestosis
- coal workers pneumoconiosis
- silicosis (inhalation of crystalline silica dust)
What are some treatment related interstitial lung diseases?
- radiation
- methotrexate
- chemotherapy
- amiodarone
- methotrexate
What are some connective tissue interstitial lung diseases?
- rh. arthritis
- schleroderma
What are some immunological interstitial lung diseases?
- sarcoidosis
- ext. allergic alveolitis
What is respiratory stress syndrome in a new born?
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
How do you treat RDS?
Surfactant replacement via endotracheal tube, and supportive treatment with oxygen and assisted ventilation
What is emphysema?
Loss of elastin and breakdown of alveolar walls, causing increased lung compliance, decreased elastic recoil, narrowing of small airways (irreversible) , loss of alveolar SA
What is emphysema a feature of?
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
What does loss of elastin fibres in emphysema cause?
- 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
What are the symptoms of emphysema?
- shortness of breath
- reduced exercise tolerance
- cough
What is a rarer cause of emphysema?
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
What is asthma?
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
What is a pneumothorax?
A disorder where air enters the pleural space, with loss of pleural seal and lung collapse
How does a pneumothorax occur?
- 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
What is atelectasis?
Incomplete expansion of the lungs (neonatal atelectasis) OR the collapse of a previously infalted lung
What are the main types of acquired pulmonary atelectasis in adults?
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
