Pulmonary emphysema: causes, symptoms, diagnosis, tests, treatment
Pulmonary emphysema (a term originating from the Greek empbysan, meaning ‘to swell’) is an obstructive lung disease characterised by the dilation and destruction of the lung parenchymal units, from the terminal bronchioles to the alveoli
Technically, confirmation of the pathological picture can only be obtained by lung biopsy or autopsy examination; however, certain clinical and diagnostic findings, which will be listed throughout this article, are highly suggestive of this pathological process.
The onset of symptoms typically occurs after the age of 50 and affects men about 4 times more than women.
Classification of pulmonary emphysema
Emphysema can be classified according to the anatomical location of the disease process. Panlobular (panacinous) emphysema consists of enlargement of the air spaces distal to the terminal bronchioles, comprising the respiratory bronchioles, alveolar ducts and alveoli, and is most frequently caused by a deficiency of the α1-proteinase inhibitor (α1PI).
In contrast, centrolobular emphysema primarily involves the mid-acinar respiratory bronchioles, thus sparing the distal pulmonary units.
Causes and risk factors of pulmonary emphysema
The two main factors identified in the progression of pulmonary emphysema are cigarette smoking and genetic predisposition to develop the disease.
The most common factor associated with the development of pulmonary emphysema is, as is unfortunately often the case with respiratory diseases, a positive history of cigarette smoking.
The exact mechanism and role of cigarettes in the development of the disease are unknown.
Inhaling cigarette smoke increases protease activity, which in turn destroys the terminal bronchioles and alveolar walls.
Smoking also reduces muco-ciliary transport, leading to retention of secretions and increased susceptibility of the lung to infectious processes.
Although smoking appears to be the main cause of emphysema in most cases, a small number of individuals develop pulmonary emphysema with little or no exposure to smoke as a result of congenital deficiency of the α1PI enzyme.
Normally, the liver produces 200-400 μg/dl of this serum protein, formerly called α1-antitrypsin.
α1PI is responsible for the inactivation of elastase, an enzyme released by polymorphonuclear leucocytes (PMNs) and macrophages, which degrades elastin during the inflammatory response.
Therefore, an alI deficiency leads to elastase-induced destruction of lung tissue, resulting in panlobular emphysema.
This pathological picture is a consequence of a genetically inherited homozygous trait present in approximately 1% of emphysema cases that first become symptomatic in the third to fourth decade of life. Cigarette smoking also aggravates the anatomopathological picture observed in α1PI deficiency.
Respiratory infections contracted during childhood can lead to the development of obstructive lung disease later in life, and inhaled pollutants such as sulphur dioxide and ozone can also increase the morbidity of patients with pneumopathy.
Although the exact role of inhaled pollutants in the aetiology of pulmonary emphysema is not elucidated, exacerbations of the disease may occur when pollutant levels are elevated.
Based on these data, patients should avoid infections and inhalation of irritants, thus preventing disease exacerbations.
Pathophysiology
Due to the tissue destruction and loss of elastic properties that occur in pulmonary emphysema, there are limitations in exhalation and abnormalities in gas exchange.
The alteration of expiratory flow results from the loss of the elastic properties of the lung tissue, which leads to a reduction in the thrust pressure of exhaled air, an increase in lung distensibility and collapsibility of the airway walls.
These eventually lead to air entrapment during forced exhalation and an increase in functional residual capacity, residual volume and total lung capacity.
Destruction of the pulmonary capillary alveolar bed, on the other hand, leads to a reduction in the gas exchange surface area, while dilation of the airways increases the distance for gas exchange and both of these phenomena alter the efficiency of external respiration.
These abnormalities eventually lead to imbalances in the ventilation/perfusion (V/Q) ratio with large areas of ventilatory dead space and increased work of breathing.
Diagnosis: anamnesis
The findings of emphysema usually occur in association with those of chronic bronchitis.
However, for didactic purposes, the signs and symptoms displayed by emphysematous, ‘pink puffer’ patients will be described to differentiate these two processes.
As stated earlier, a definitive diagnosis can only be made after an anatomopathological examination of the patient’s lung tissue; however, the history, clinical examination and results of diagnostic tests will often be able to provide adequate information to confirm the clinical diagnosis of pulmonary emphysema.
The patient often complains of dyspnoea that increases with exertion while dyspnoea at rest appears relatively late in the course of the disease.
Exacerbations of the disease process typically occur after viral or bacterial respiratory infections, as a consequence of exposure to dust or in association with congestive heart failure.
A history of cigarette smoking should alert the physician to the possibility that the patient may develop not only pulmonary emphysema but also other smoking-related respiratory diseases such as chronic bronchitis.
A positive family history of α1PI deficiency should also alert the physician as the signs and symptoms of pulmonary emphysema may develop earlier in such patients.
Diagnosis of pulmonary emphysema: objective examination
The clinical examination of the patient can provide key information in establishing the diagnosis of pulmonary emphysema.
Inspection of the patient with pulmonary emphysema will frequently show the presence of tachypnoea with prolongation of the expiratory phase, tachycardia, use of accessory muscles of respiration, increased antero-posterior diameter of the chest and sometimes exhalation with half-closed lips.
Patients also often assume a body position whereby they can lean forward with their arms fixed to their knees or with their elbows resting on the table.
This position provides an optimal mechanical advantage for the respiratory muscles.
Palpation usually shows a reduction in tactile vocal quivering, while percussion shows flattened and immobile haemidiaphragms and increased resonance above the lung fields.
Auscultation of the chest shows reduced lung sounds as well as reduced transmission of heart tones and voice.
Diagnosis: examinations
A chest X-ray shows hyperdiaphanous, expanded lung fields with low, flattened diaphragms and a small, vertically oriented heart.
Chest X-ray in lateral projection shows increased transparency of the retrosternal lung fields.
Pulmonary function studies (spirometry), although not routinely performed during acute exacerbation, show an increase in residual volume (RV), functional residual volume (FRC) and total functional capacity (TLC) due to air entrapment.
The forced vital capacity (FVC), expiratory volume in 1 second (FEV1) and FEV/FVC ratio, on the other hand, decrease due to airflow obstruction.
The reduction in DLco reflects the loss of air surface area resulting from destruction of the alveolar and pulmonary vascular bed.
The blood gas values of an emphysematous patient typically do not reflect the severity of the disease process.
Common changes include respiratory alkalosis with moderate hypoxaemia in mild-to-moderate forms of emphysema and the development of respiratory acidosis with more marked hypoxaemia during the terminal stages of the disease.
Although the electrocardiogram (ECG) is not diagnostic for emphysema, it provides useful information on the patient’s condition.
The more vertical position of the heart associated with the more pronounced lung hyperinflation and flattening of the diaphragmatic dome results in a rightward shift of the electrical axis of the P wave and QRS complex in the frontal plane.
High and sharp P waves, indicative of atrial enlargement (pulmonary P), may also be present.
Pulmonary hyperinflation also reduces the amplitude (voltage) of the electrical waves in the limb leads.
Therapy in the patient with pulmonary emphysema
The treatment of pulmonary emphysema includes both acute and supportive therapy.
Acute phase therapy should reduce the work of breathing and ensure optimal oxygenation and ventilation.
Long-term therapy, on the other hand, is designed to reduce morbidity and increase the patient’s autonomy and quality of life.
The benefits of the pulmonary rehabilitation programme for the emphysematous patient include both the information to be provided to the patient about his disease and a set of chronic treatments.
Careful long-term respiratory treatment reduces symptoms and the length of hospital stay.
It also increases exercise tolerance and the ease with which daily activities are performed, reduces anxiety and depression, and thus improves the patient’s quality of life.
Supplemental oxygen therapy is useful when the PaO in room air is less than 55 mmHg.
In patients with pulmonary emphysema, adequate oxygenation can usually be achieved by means of a nasal cannula with flows of less than 3 litres/minute.
If, on the other hand, an acute exacerbation has been precipitated by a pneumonic episode or congestive heart failure, hypoxaemia may be significant and require a more significant increase in FiO2.
Treatment of acute crises includes stabilising the patient’s respiratory condition and treating the exacerbating cause.
Medications of importance in the treatment of bronchospasm associated with emphysema exacerbations are bronchodilators: anticholinergics, methylxanthines and β2-stimulants.
The latter are both short-acting and long-acting such as salmeterol.
Methylxanthines also increase diaphragm contractility.
Steroids, on the other hand, reduce the inflammatory response in the airways and are useful in certain patients.
In addition, anticholinergic bronchodilators are particularly useful in treating bronchospasm due to increased sympathomimetic tone.
Antibiotics are indicated in the presence of a bacterial respiratory infectious process, typically diagnosed on the basis of changes in the physical characteristics of sputum (quantity, colour, consistency).
Diuretics are useful when congestive heart failure complicates the patient’s clinical condition.
In cases where expectoration of secretions is a major problem during acute exacerbations, the physician should encourage the patient to engage in lung hygiene improvement techniques such as respiratory physiotherapy and humidification of secretions.
In a patient with an α1PI deficiency, replacement treatment can be instituted.
Acute respiratory failure may require the institution of continuous mechanical ventilation (CMV) to maintain adequate ventilatory balance in the patient.
CMV proves to be a more rational choice when respiratory failure is the result of a reversible problem superimposed on chronic obstructive pulmonary disease (COPD).
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