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Basic alveolar anatomy
- Type I pneumocytes
- ->95% of alveolar surface area
- -thin, limited organelles
- -minority of alveolar cell population (?)
- -primary role: gas exchange
- -some ion exchange, regulation of fluid
- -susceptible to injury
- -unable to replicate
- Type II pneumocytes
- -Cuboidal
- -Majority of alveolar cell population (?)
- -primary role: surfactant production, fluid balance, stem cells for type I
- -lamellar bodies
- -replicate on demand
- -differentiate to replace injured type I cells
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Gas exchange
- 1. Diffusion gradient from alveolus to capillaries
- -PAO2 = FiO2*(Patm - PH2O) - (PaCO2/RQ)
- 2. Time for diffusion
- -typically requires ~0.25 seconds
- -capillary travel time ~0.75 seconds
- 3. Alterations of parenchyma have variable effects on oxygenation
- -increased diffusion time (typically insignificant; time remains below 0.75sec)
- -V/Q mismatching (always important)
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Diffuse parenchymal lung disease
general characteristics
- Destruction and distortion of the parenchymal anatomy
- Thickening of alveolar/capillary interface
- infiltration with immune cells
- alveolar filling
- bronchialar destruction or narrowing
- granulomas
- fibroblastic foci
- traction bronchiectasis
- fibrosis and honeycombing
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Diffuse parenchymal lung disease
Chategories
- Autoimmune disease
- inhaled toxins or particulates
- drug-induced
- radiation-induced
- hormonal contributions
- associations with smoking
- idiopathic
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- "classic" CT for parenchymal disease
- (i.e. pulmonary fibrosis)
- -some cystic changes
- -honeycombing
- -ground glass
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Compliance
- Compliance is the change in volume for a given change in pressure
- C=ΔV/ΔP
- parenchymal lung disease decreases lung compliance
- increased effort (pressure) to fill lung to same volume --> Sx
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Diffuse parenchymal lung disease
general symptoms and findings
- VARIABLE SX:
- -Dry cough
- -Shortness of breath
- -Shallow breathing
- -Swelling in ankles (R heart failure)
- -Syncope
- -asymptomatic (incidental finding on CXR)
- -Acute respiratory decompensation
- Exam findings:
- -Dry crackles ("Velcro" crackles)
- -Clubbing
- -Enhanced or split P2
- -Hypoxemia (especially with exertion)
- -Cachexia --increased work of breathing
- -Rheumatologic findings (arthritis, dermatitis, myositis, joint deformities)
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Pulmonary Function
in diffuse parenchymal lung disease
- May find restrictive, obstructive, or combined pattern
- -Restriction is the most common pattern
- Reduced DLCO "out of proportion" with volumes
- -i.e. vital capacity ~70%, and DLCO ~30%
may find hypocapnia and hypoxemia
- Oxygen deseaturation with exertion is very common
- -V/Q mismatching
- -+/- impaired diffusion
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Pneumoconioses
Chronic inhalation of small particulates that deposit into smallest airways, alveoli
Disease is caused by immune system reaction to the accumulated particulates (i.e. alveolar macrophages)
- Tx: Avoidance, protective equipment
- -most industries now regulate exposure and require protective equipment
**Predisposition for pulmonary infections, especially Mycobacteria
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Silicosis
- Chronic inhalation of very fine silicates (quartz)
- -sandblasters, miners, demolition, sanders
- Pathophysiology:
- -engulfed by alveolar macrophages
- -activation, destruction, re-engulfment cycle
Presentation: progressive parenchymal destruction
- Simple silicosis: small nodules on imaging
- Complicated silicosis: coalescence of nodules, extensive fibrosis, cavities, ...
- -demonstrates volume loss: R mainstem bronchi is higher than it should be
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Coal-worker's pneumoconiosis
- Coal dust exposure
- Fibrous and emphysema seen in respiratory bronchioles
- Classifications: simple vs complicated
- Coal macules
seen on pathology
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Asbestosis
Derivative of silica: straight, sharp, crystalline fibers
-Chronic exposure: insulation, shipworkers, pipefitters, break pads, Turkey! (NAVY)
- Deposition of fibers into respiratory bronchioles and alveoli
- -engulfment by macrophages...
- -Alveolitis, peribronchial fibrosis, subpleural cysts
- -Ferruginous bodies: Asbestos fibers coated in iron/protein complex by alveolar macrophages:
- Pleural disease is common
- -Benign asbestos pleural effusion (BAPE)
- -Calcified pleural plaques (calcified lesions mostly benign) ... easy to see on CT
- Associated with neoplasia:
- -Adenocarcinoma
(especially increased risk when combined with smoking) - -Mesothelioma (less common)
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Asbestosis ≠ exposure
- Asbestosis
- -Fibrotic, destructive process, which can lead to progressive symptoms, disability or death
- Asbestos exposure along:
- -may find calcified nodes, effusions, or pleural plaques
- -fibrotic parenchymal changes are ABSENT
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Berylliosis
- Chronic exposure to beryllium dust
- -Electronic industry, military jet pilots or mechaniccs, aerospace workers, nuclear weapons
Clinically may mimic sarcoidosis
- Dx: Beryllium Lymphocyte Proliferation Test (BeLPT)
- -Measures response of pt's lymphocytes to beryllium exposure
- -Pts with berylliosis will show hypersensitive (T cells)
- -68% sensitive; 97% specific
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Hypersensitivity pneumonitis
- Collection of parenchymal diseases that are characterized by extrinsic allergic alveolitis
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Robust immunologic reaction to inhaled organic matter
- *typically improves with avoidance
- -pts often asked to change habits to see test exposures
-Type III or Type IV hypersensitivity reaction
- Acute:
- -Sx within hrs
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fever, chills, dyspnea, cough - -May mimic pneumonia
- Subacute:
- -similar to acute, slower onset and less severe
- Chronic: Most common
- -Progressive to fibrosis, permanent disease
- -Historical link may be difficult to find
- Dx:
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History - Pathology: Noncaseating granulomas
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cholesterol clefts - -Foamy macrophages
- Radiography:-infiltrates seen along the bronchovascular bundles-fibrosis and honeycombing when advanced or chronic
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Hypersensitivity pneumonitis
names
- Bird fancier's lung
- Hot tub lung
- Farmer's lung
- Crack lung
- Maltworker's lung
- Popcorn worker's lung
- Penguin humidifier lung
- Cheese-washer's lung
- Japanese summer house hypersensitivity pneumonitis
- Wine-grower's lung
- ...
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