Obstructive Lung Disease Flashcards
Pulmonary function test findings for obstructive lung disease.
FEV1 reduced <70%
Pulmonary function test findings for restrictive lung disease
FVC reduced <80% FEV1 reduced FEV1% normal
TLC in obstructive lung disease
TLC increases (through gas trapping), although the ability of the lung to exchange oxygen and CO2 is reduced.
The two situations in which restrictive lung disease occurs
- Chest wall disorders in the presence of normal lungs (e.g. polymyelitis, severe obesity, pleural disease and kyphoscoliosis) 2. Acute (diffuse alveolar damage) or chronic interstitial and infiltrative diseases (e.g. pulmonary fibrosis)
TLC in restrictive lung diseases
Reduced.
Disorders associated with airflow obstruction
- Chronic bronchitis 2. Bronchiectasis 3. Asthma 4. Emphysema 5. Bronchiolitis
Chronic Obstructive Pulmonary Disease
Emphysema and chronic bronchitis occurring together. Often occur together because of common aetiology: cigarette smoking. In most patients COPD is the result of cigarette smoking but about 10%.
Emphysema
Characterised by abnormal permanent enlargement of the airspaces distal to the terminal bronchiole, accompanied by destruction of their walls and without obvious fibrosis. It is usually associated with chronic bronchitis and follows a chronic progressive course.
Classification of emphysema
Classified according to the anatomical distribution within the lobule. 1. Centriacinar (centrilobular) 2. Panacinar (panlobular) 3. Distal acinar (paraseptal) 4. Irregular The first two types cause significant airflow obstruction. Centriacinar emphysema constitutes more than 95% of cases.
Cenriacinar (centrilobular) emphysema
The central or proximal parts of the acini, formed by respiratory bronchioles, are affected, whereas distal alveoli are spared. This form tends to be worse in the upper lobes and is strongly associated with smoking. Carbon pigment is often seen in the alveolar walls.
Panacinar (panlobular) emphysema
The acini are uniformly enlarged from the level of the respiratory bronchiole to the terminal blind alveoli. This is usually associated with alpha-1 antitrypsin deficiency and is worse at the lung bases.
Distal acinar (paraseptal)
The proximal portion of the acinus is normal, but the distal part is predominantly involved. It is worst adjacent to the pleura, along the lobular CT septa, and at the margins of the lobules. It occurs adjacent to areas of fibrosis, scarring, or atelectasis and is usually more severe in the upper half of the lungs. It is associated with spontaneous pneumothorax in young adults.
Irregular emphysema
The acinus is irregularly involved, is almost always associated with scarring. It may be the most common form of emphysema because careful search of most lungs at autopsy shows one or more scars from a healed inflammatory process. These foci of irregular emphysema are asymptomatic and clinically insignificant.
COPD pathogenesis
Characterised by mild chronic inflammation throughout the airways, parenchyma and pulmonary vasculature. The best explanation for the development of emphysema is the protease-antiprotease theory which holds that alveolar wall destruction results from an imbalance between proteases (mainly elastase) and antiproteases in the lung. Chronic irritation and inflammation (e.g. in cigarette smoking) causes increased neutrophils (the principal source of cellular proteases (which include elastase) into the lung and these release their protease granules. Protease activity and deficiency of protease inhibitors causes overall decreased antiprotease activity resulting in elastic tissue destruction. Macrophages, free radicals (oxidants)/antioxidant imbalcne, elastases and metalloproteinases are also imporant.
Whats the most commonly deficient protease inhibitor?
alpha-1 antitrypsin (alpha1-AT). This is a anti-protease usually present in serum, tissue fluids and macrophages and is a major inhibitor of neutrophil elastase. An inhereted deficiency of alpha1-AT occurs secondary to mutations in the protein inhibitor (Pi) gene which determine the type and amount of alpha1-AT. Those with two Z alleles have 15-20% of normal alpha1-AT. 80% of these individuals are clinically diagnosed with emphysema by the age of 40. The alpha1-AT accumulates in the liver and can lead to cirrhosis.
Morphology of emphysema
Regardless of the histological subtype, emphysema causes hyperinflation of the lung. This is most dramatic in panacinar emphysema. In advanced emphysema, the development of large bullae (blisters) occurs, usually in areas of scarring. There is often an associated bronchitis and bronchiolitis. Changes seen int he bronchioles include goblet metaplasia, with mucus plugging, inflammatory cell infiltrate, wall thickening due to smooth muscle hypertrophy and peribronchial fibrosis. Loss of elastic recoil and bronchiolitis contribute to airways obstruction. The process may continue for decades despite smoking cessation.
Chronic bronchilitis
Is defined clinically. It is present in any patient who has persistent cough with sputum production for at least 3 months in at least 2 consecutive years, int he absence of any other identifiable cause.
Chronic bronchitis aetiology
Long standing irritation with tobacco smoke (most commonly) or polluted air(smog/dust).
Pathogenesis chronic bronchitis
The earliest feature is hypersecretion of mucus associated with mucus gland hypertrophy and an increased Reid index in the trachea and bronchi. Proteases from neutrophils stimulate mucous hypersecretion. As chronic bronchitis persists there is a marked increase in goblet cells in the small bronchi and bronchioles. This goblet cell metaplasia, leads to increased numbers of goblet cells resulting in increased mucous and mucous plugging. Often there is secondary bacterial or viral infection.
Reid index
Thickness of mucous gland layer/thickness between the epithelium and cartilage; N is 0.4
Macroscopic morphology of chronic bronchitis
Hyperemia, swelling and oedema of the mucous membranes frequently associated with mucous/mucopurulent secretions.
Microscopic morphology of chronic bronchitis
Major change is the presence of chronic inflammation of the airways and mucous gland hyperplasia resulting in an increase in the Reid index. The bronchial epithelial may exhibit squamous metaplasia and dysplasia.
Clinical course of COPD
Dyspnoea is usually the first symptom. In some patients, cough or wheezing is the chief complaint, this may be confused with asthma. Cough and phlegm production are extremely variable and depend on the extent of the associated bronchitis. Weight loss is common. Classically in emphysema, the patient is barrel-chested and dyspnoeic, with prolonged expiration. As the disease progresses patients compensate by hyperventilating and remain well oxygenated (pink puffers). With further progression or acute infective exacerbation or chronic bronchitis, they retain CO2, become cyanosed and develop fluid retention secondary to right heart failure (blue bloaters).
Cause of death in COPD
- Respiratory acidosis and coma 2. Right sided heart failure; and 3. Massive collapse of the lungs secondary to pneumothorax
