Chronic bronchitis and emphysema - Respiratory infections

Chronic bronchitis and emphysema

Definition

Chronic bronchitis has a clinical definition of cough productive of sputum on most days for at least 3 months of the year for more than 1 year. Emphysema is defined as dilation and destruction of the lung tissue distal to terminal bronchioles. The two frequently coexist to varying degrees as chronic obstructive pulmonary disease (COPD).

Prevalence

COPD has a prevalence of 12% aged 40–64 years. Emphysematous spaces are found in 50% of smokers aged over 60 at autopsy.

Age

Incidence increases with age.

Sex

M > F

Geography

Follows patterns of smoking.

Aetiology

Virtually confined to cigarette smokers and related to the number of cigarettes smoked each day. There is a strong genetic element to both components of COPD.

α1-antitrypsin deficiency is a recessive disorder, which causes panacinar emphysema and accounts for 5% of patients with emphysema. One in 5000 births have a homozygous deficiency and most these go on to develop the lung disease. Patients tend to be young (below 40 years) especially if smokers, in whom the disease is much worse.

Pathophysiology

There is airway inflammation, dominated by neutrophils and CD8+ T cells. There is also hypertrophy and hyper-plasia of the mucus secreting glands causing plugging of airways and luminal narrowing resulting in airway obstruction. This ‘chronic bronchitis’ coexists with a greater or lesser degree of emphysema in this patient group.

·        In centriacinar emphysema there is distension of alveoli and damage of lung tissue concentrated around the respiratory bronchioles whilst the more distal alveolar ducts and air spaces tend to be well preserved. The alveolar dilatation results from loss of elastic recoil in the terminal bronchioles, as a result of destruction of lung tissue by neutrophil derived proteases. Smoking also causes glandular hypertrophy (chronic bronchitis) and has an adverse effect on surfactant favouring over distension of the lung.

·        In panacinar emphysema destruction involves the whole of the acinus.

Clinical features

Chronic bronchitis and emphysema together produce the clinical picture of COPD (also sometimes called chronic obstructive airways disease (COAD), or chronic obstructive lung disease (COLD)). In addition there may be features of asthma as some patients have a degree of reversible airflow obstruction. The clinical features depend on the degrees of chronic bronchitis and of emphysema contributing to the overall picture.

·        Symptoms of chronic bronchitis include cough productive of sputum, expiratory wheeze and progressive shortness of breath. Symptoms of emphysema are dominated by progressive breathlessness, initially only on exertion but eventually on mild exertion such as dressing. Expiratory wheeze and cough are present but the cough is dry.

·        Signs in both diseases include expiratory wheeze heard in all lung fields, in chronic bronchitis coarse early inspiratory crackles are also heard. As emphysema becomes more severe other signs become evident including tachypnoea, cachexia, the use of accessory muscles of respiration, intercostal recession, pursed lips on expiration, poor chest expansion (a hyperinflated chest at rest) and loss of cardiac and hepatic dullness due to hyperinflation.

·        The two patterns of pink puffer (always breathless, not cyanosed, cachexic) and blue bloater (obese, cyanosed, hypoventilating, often with little respiratory effort) describe the extremes of the spectrum of disease manifest as COPD. The pink puffer is typical of relatively pure emphysema and the blue bloater is typical of relatively pure chronic bronchitis.

Macroscopy

There is secretion of abnormal amounts of mucus causing obstruction and plugging of the airways. Mucus gland hypertrophy and hyperplasia can be quantified by the Reid index which is the ratio of gland to wall thickness within the bronchus.

Microscopy

Both emphysema and chronic bronchitis are inflammatory diseases of the lung. The inflammatory infiltrate is dominated by neutrophils and CD8 +ve T cells. Eosinophils are also seen especially in chronic bronchitis, in which the predominant pathological features are mucus gland enlargement and airway wall inflammation. In emphysema the predominant feature is destruction of the alveolar septae as a result of neutrophil derived proteases. Acute viral or bacterial infections, or chronic bacterial colonisation exacerbates the inflammation. Squamous metaplasia is commonly seen.

Complications

Airway obstruction and alveolar destruction eventually leads to impaired alveolar ventilation and respiratory failure in both conditions. Pulmonary vasculature responds to hypoxia by vasoconstriction which increases the arterial pressure, causing pulmonary artery hyper-tension, which leads to right heart failure (cor pulmonale). There may be secondary polycythaemia due to hypoxia. In emphysema initially hyperventilation maintains normocapnia. Cyanosis, hypercapnia and cor pulmonale develop only late in the disease after progressive decline in lung function. Amoxycillin resistant Haemophilus respiratory infections are common in COPD patients as a result of frequent courses of antibiotic therapy. Acute exacerbations precipitated by viral, bacterial or mixed infections are common resulting in major morbidity and mortality.

Investigations

The diagnosis is frequently made clinically but requires confirmation by demonstration of degree of irreversible airway obstruction manifest by a reduced PEF and FEV1/FVC after inhaled bronchdilators. In emphysema the KCO (transfer factor) is also reduced. The lung volumes may be normal in chronic bronchitis but are increased in emphysema.

·    Chest X-ray: May be normal or there may be bullae, severe over-inflation. There may also be a deficiency of blood vessels in the peripheral half of the lung fields in comparison to the proximal vessels.

·    CT scan is usually performed to assess the degree of alveolar destruction due to emphysema. It frequently shows peribronchial thickening and alveolar coalescence.

·    Haemoglobin and packed cell volume may be ele-vated.

·    Blood gases are variable as there may be hypoxia and hypercapnia or hypocapnia, depending on the degree of type I or type II respiratory failure and the degrees of respiratory and metabolic compensation.

·    ECG for cor pulmonale (right axis deviation, tall R in V1, peaked P waves) and coexisting cardiac disease.

·    α1-antitrypsin (normal serum range 20–48 mmol/L).

Management

1. Non-pharmacological: By far the most important factor that can affect the prognosis and progression of chronic obstructive pulmonary disease is stopping smoking. Weight loss is vital in the obese. Physiotherapy may help clear sputum, and pulmonary rehabilitation programmes improve exercise capacity and quality of life. Influenza vaccine should be given annually.

2. Pharmacological

Bronchodilators: Short acting bronchodilators produce significant clinical benefit, helping patients feel less short of breath (although objective improvement in lung function tests may be slight).

Salbutamol is usually first line therapy followed by ipratropium bromide. Long acting β2 agonists and long acting anticholinergics improve lung function, symptoms, reduce exacerbation frequency and are recommended for moderate COPD. Long-term oral theophylline appears to be of some benefit.

Inhaled corticosteroids have been shown to produce small improvements in lung function, to reduce exacerbation frequency and to slow the decline in FEV1 over time. The optimum dose and patient group in which they should be used are not yet clearly defined. They are currently recommended for moderate-severe COPD with two or more exacerbations in the last 12 months.

An oral course of prednisolone, and antibiotics if sputum is purulent, should be given promptly in acute exacerbations in an attempt to minimise lung damage. Amoxycillin resistant Haemophilus respiratory infections are treated with erythromycin, co-amoxiclav or cephalosporins.

Diuretic therapy for oedema in patients with right heart failure.

3. Persistent hypoxia should be treated with long-term domiciliary oxygen therapy to improve prognosis.

4. Non-invasive nasal ventilation is useful in treating acute exacerbations to avoid the need for intubation and formal ventilation. It can also be used for nocturnal hypoxic episodes and to prolong life, e.g. prior to planned transplantation.

5. α1-antitrypsin infusions are used as replacement for patients with serum levels below 11 mmol/L and abnormal lung function, but it is not known if this improves the prognosis.

6. Surgical management

·        Patients of young age who are otherwise fit and well may be considered for lung or heart/lung trans-plantation. The heart/lung transplant requires car-diopulmonary bypass and is performed through a sternotomy. Bilateral or single lung transplants are performed through a lateral thoracotomy possibly without bypass. Immunosuppression is achieved with triple therapy of cyclosporin, azathioprine and steroids. The lung is prone to rejection and thus transbronchial biopsies are now used for routine monitoring. Infection is common and may be severe.

·        Lung volume reduction surgery has a place in the treatment of some patients with emphysema although its role is still under investigation.

Prognosis

50% of patients with severe breathlessness die within 5 years although even in severe cases stopping smoking improves the prognosis.