Emphysema Health Article

EMPHYSEMA

Emphysema is a lung disease that, along with chronic bronchitis, represents a type of chronic obstructive pulmonary disease (COPD). Medical scientists have defined emphysema as "a condition of the lung characterized by abnormal, permanent enlargement of airspaces distal to the terminal bronchioles, accompanied by the destruction of their walls, and without obvious fibrosis" (Snider 1985).

COPD is the fourth leading cause of death in the United States, accounting for about 113,000 deaths annually. About 14 million Americans have symptoms of COPD. Among these, 1.65 million have emphysema. Millions more likely have undiagnosed or incipient COPD. The prevalence of COPD peaks in the sixty-five to seventy-four age range, and men are affected more than women.

Pathologists recognize three major types of emphysema: localized (distal acinar, paraseptal), centrilobular (centriacinar), and panlobular (panacinar). Centrilobular emphysema, the most common of the three, is usually caused by cigarette smoking. Cigarette smoke is thought to cause chronic inflammation in the walls of the air sacs (alveoli) of the lung, leading to an imbalance between destructive proteases and protective protease inhibitors. The proteases, such as elastase, gradually destroy the structural proteins (elastin, collagen) in the alveolar walls. Substantial variation in individual susceptibility to cigarette smoke exists, as only about one in seven cigarette smokers develops symptoms of COPD. Other than cigarette smoking, the only condition clearly linked to emphysema is a hereditary disorder called alpha₁-antitrypsin deficiency (AAT). This rare condition, which is found in less than one percent of patients with COPD, occurs because the blood level of a glycoprotein (protease inhibitor) is not sufficient to counteract the activity of the proteases. Coal miners and workers chronically exposed to cadmium fumes are at risk to develop emphysema. The effects of other occupational agents, air pollution, and familial factors in the pathogenesis of emphysema are not clear.

Destruction of alveolar walls in emphysema reduces the lung's elasticity, which results in obstruction to airflow in small airways, trapping air in the lung. Other pathophysiologic findings in emphysema include increased lung compliance, elevation of the pressure in the pulmonary arteries (pulmonary hypertension), and abnormal matching of air flow and blood flow (ventilation/perfusion imbalance), which causes hypoxemia (low oxygen level in the blood).

Patients with emphysema suffer from shortness of breath (dyspnea), which typically appears between the ages of fifty and sixty. Initially, the dyspnea is noted only with heavy exertion, but it progresses over time to a persistent, daily symptom that may eventually limit simple activities and even be present at rest. If the patient also has chronic bronchitis, daily cough and sputum production are present. Physical examination in emphysema reveals chest hyperinflation (overdistention) and reduced breath sounds on auscultation (listening to breathing noises with a stethoscope). In severe cases, there may be signs of respiratory failure and failure of the right side of the heart (cor pulmonale).

The clinical diagnosis of emphysema is suggested by the presence of a risk factor for emphysema (smoking and/or AAT), the clinical findings described above, the absence of alternative diagnoses to explain these findings (e.g., bronchial asthma, bronchiectasis, and central airways obstructive diseases), and evidence of airflow obstruction on spirometry (pulmonary function testing). Airflow obstruction in emphysema is usually irreversible, meaning there is no improvement in the obstruction after inhaling a bronchodilator drug. Specialized pulmonary tests may demonstrate air trapping and reduction in the gas-transfer ability of the lung. The chest radiograph in mild emphysema may be normal, but in severe cases there is hyperinflation. Sometimes large air sacs called bullae are seen. Computed tomographic imaging may confirm lung destruction, bullae, and hyperinflation. Arterial blood-gas analysis and transcutaneous measurement of oxyhemoglobin saturation (oximetry) reveal hypoxemia in advanced emphysema.

Emphysema is treated with a broad-based approach that includes elimination of cigarette smoking, immunization against influenza virus and Streptococcus pneumoniae infection, exercise, maintenance of a healthy lifestyle, and the use of bronchodilator medications (e.g., ipratropium bromide and albuterol). Supplemental oxygen is prescribed if hypoxemia is present. Continuous long-term oxygen therapy improves survival in COPD patients with hypoxemia. Anti-inflammatory drugs such as corticosteroids are helpful in a small percent of emphysema patients. COPD exacerbations, with increasing dyspnea, cough, and sputum production, are usually treated with intensification of the bronchodilator regimen, antibiotics, supplemental oxygen, and in some cases corticosteroids. Hospitalization may be necessary, and in severe cases insertion of a breathing tube into the airway (endotracheal intubation) and mechanical ventilation are necessary. Debilitated COPD patients may benefit from comprehensive outpatient rehabilitation. Rarely, patients with advanced emphysema are treated surgically (removal of large bullae, volume reduction surgery, or lung transplantation).

With the exception of AAT, emphysema is a preventable disease. Smoking abstinence remains the best hope for reducing the morbidity and mortality associated with emphysema. Early detection of airflow limitation in young cigarette smokers may provide a strong stimulus to quit smoking. This is important because smoking cessation is known to slow the rate of decline in lung function in middle-aged smokers with mild COPD.

Survival in patients with COPD is determined by multiple factors, including age, gender, lung function, and levels of oxygen and carbon dioxide in the blood. The prognosis is worse when the airflow obstruction is irreversible. COPD patients with severe obstruction, as defined by spirometry, have a median survival of about four to five years, but there is substantial variability. Death in emphysema patients is usually a result of pneumonia, lung cancer, heart disease, or respiratory failure.

JOHN L. STAUFFER

(SEE ALSO: Asthma; Chronic Respiratory Diseases; Pulmonary Function; Smoking Behavior; Smoking Cessation; Tobacco Control)