Pathology of Restrictive Lung Disease

restrictive-diffuse-interstitial lung disease

reduced lung compliance-stiff lungs

low FEV1 & low FVC but FEV1/FVC normal ratio because no limitation to air moving in and out, just less air to move in n out

reduced gas transfer-diffusion abnormality

ventilation/perfusion imbalance when small airways affected by pathology

Main physiological problem is gas diffusion

dyspnoea shortness of breath on exertion → shortness of breath at rest (as disease progresses)

patient may have type 1 respiratory failure with hypoxaemia, with cor pulmonale and heart failure

emphysema, increased lung volume as they have to maintain more air in lungs for small airways to breath in and out

interstitial reduced lung volume as less space for air?

the end result is irreversible

UIP almost inevitable to end up with pulmonary fibrosis

granulomatous less likely to progress into end stage fibrosis

diffuse alveolar damage (DAD) also known as acute respiratory distress syndrome (ARDS)

is an acute inflammatory process

not only leaking of capillary walls but damage of epithelial cells, leaks into alveolar air space, fills lungs with fluid

protein becomes deposited around alveoli

after a few days becomes more chronic

ultimately fibrosis follows as an attempt to heal

pink layer is hyaline membrane

mechanism to repair and heal kick in but don’t work very well

less than 50% make it out of Intensive care, most die

Sarcoidosis is a multisystem granulomatous disorder of unknown aetiology (unknown cause)

evidence of type 4 hypersensitivity reaction, but to what? They don’t know

histopathology: epithelioid and giant cell granuloma

necrosis/caseation very unusual

very few lymphocytes associated with these granulomas, little lymphoid infiltrate

variable associated fibrosis

commonly affects young adults, female > male

100% involvement of lymph odes in sarcoidosis, >90% etc

Hypersensitivity Pneumonitis : The antigens

inhaled (often organic) antigens

thermophilic actinomycetes

farmers lung, breathes in all the organisms from the wet hay

bird fanciers lung, develop hypersensitivity to feathers or bird poo

feathers from duvet

some patients with hypersensitivity pneumonitis might present like they have pneumonia but it is more chronic

type 3 & 4 hypersensitivity reactions

lots of granulomas and interstitial

dominates in upper zone of the lungs

hypersensitivity pneumonitis is a bit more likely to give you fibrosis

UIP, 5 year survival of 30%, inevitably a progressive disease

UIP is commonly idiopathic pulmonary fibrosis

also in connective tissue diseases, drugs, asbestos, viruses (can all get UIP)

histopathology of UIP is patchy interstitial chronic inflammation

progressive accumulative damaging lung inflammatory process, goes over for a long period of time

eventually die of respiratory failure

in lower images fibroblastic fossi-key pathological change indicating damage and fibrosis that will scar up and lead to damaged lung

Idiopathic Pulmonary Fibrosis

•Elderly  >50    M>F

•Pathology is Usual Interstitial Pneumonitis

•Clinically show  

•Dyspnoea, Cough,

•Basal Crackles, Cyanosis, Clubbing

•Progressive Disease : Most dead within 5 years

•CXR : Basal/Posterior, Diffuse infiltrates, Cysts, ‘ Ground Glass ’

•Restrictive PFT & Reduced Gas Transfer

•Poor Prognosis : Some fulminant, some steroid responsive

diffusion impairment means it takes LONGER for blood and alveolar air to equilibrate, particularly for oxygen

diseases impairing gas diffusion usually do NOT change CO2 levels

CO2 diffuses 20 times faster than O2 due to greater solubility

FIO_{2 = the Fraction of Inspired air which is Oxygen}

•Equilibration normally takes 0.25 seconds

•Capillary transit time normally 0.75 seconds at rest

•In disease, equilibration may take close to 0.75 seconds

•PaO₂ maintained at rest but……

•Serious falls in PaO₂ may occur on exercise as capillary transit time falls

•Hypoxaemia may be corrected by increasing FIO₂. This increases PAO₂, thus increasing rate of diffusion. Rarely clinically the sole cause of hypoxaemia

if you increase time for equilibration to occur you get closer to 0.75 seconds opportunity, if you increase and it takes longer than 0.75, patient not hypoxic at rest but when they exercise, less time available, if fibrosis and increased time for equilibration you will get breathless at exercise

severe pulmonary fibrosis, even at rest with more time, might not be long enough for equilibration to take place so patient breathless at rest