Emphysema

ANATOMY OR SYSTEM AFFECTED: Chest, lungs, respiratory system

DEFINITION: A disease of the lung characterized by persistent airflow limitation due to a chronic inflammatory response in the lungs that results in the destruction of lung alveoli, causing shortness of breath, reduced oxygen to the body, and a variety of serious complications.

CAUSES: Long-term exposure to smoke, polluted air, or other environmental toxins; infection; allergies

SYMPTOMS: Shortness of breath, labored breathing, discolored skin, wheezing, difficulty coughing and talking

DURATION: Chronic

TREATMENTS: Eliminating causes of irritation, cleaning out airways via nebulizers and intermittent positive pressure breathing machine, medications (bronchodilators, antibiotics, steroids), supplemental oxygen, surgery

Causes and Symptoms

Emphysema is a lung disease in which damage to the lungs causes shortness of breath and can lead to heart or respiratory failure. A discussion of the structure and function of the normal lung can illuminate the nature and effects of this damage.

Air—along with gases, smoke, germs, allergens, and environmental pollutants—passes from the nose and mouth into a large duct called the trachea. The trachea branches into smaller ducts, the bronchi and bronchioles (small branches of the bronchi), which lead to tiny air sacs called alveoli. The respiratory system is like an upside-down tree: The trachea is the trunk, the bronchi and bronchioles are similar to the branches, and the alveoli are similar to the leaves. The blood vessels of the alveoli carry red blood cells, which pick up oxygen and transport it to the rest of the body. The cellular waste product, carbon dioxide, is released to the alveoli from the bloodstream and then exhaled. The alveoli are supported by a framework of delicate elastic fibers and give the lung a very distensible quality and the ability to "snap back," or recoil.

The lungs and bronchial tubes are surrounded by the chest wall, composed of bone and muscle and functioning like a bellows. The lung is elastic and passively increases in size to fill the chest space during inspiration and decreases in size during expiration. As the lung (including the alveoli) enlarges, air from the environment flows in to fill this space. During exhalation, the muscles relax, the elasticity of the lung returns it to a normal size, and the air is pushed out. Air must pass through the bronchial tree to the alveoli before oxygen can reach the bloodstream and carbon dioxide can get out, because it is the alveoli that are in contact with blood vessels. The bronchial tree has two kinds of special lining cells. The first type can secrete mucus as a sticky protection against injury and irritation. The second type of cell is covered with fine, hairlike structures called cilia. These cells are supported by smooth muscle cells and elastic and collagen fibers. The cilia wave in the direction of the mouth and act as a defense system by physically removing germs and irritating substances. The cilia are covered with mucus, which helps to trap irritants and germs.

When alveoli are exposed to irritants such as cigarette smoke, they produce a defensive cell called an alveolar macrophage. These cells engulf irritants and bacteria and call for white blood cells, which aid in the defense against foreign bodies, to come into the lungs. The lung tissue itself also becomes a target for the enzymes or chemical substances produced by the alveolar macrophages and leukocytes (white blood cells). The enzymes vigorously attack the elastin and collagen of the lungs, the lung alveoli lose their elastic recoil, and air is trapped, making exhalation difficult.

Emphysema and a related disease, chronic bronchitis, in which the airways of the lung become chronically inflamed, often work in concert. They are grouped together under the term chronic obstructive pulmonary disease (COPD). Chronic bronchitis weakens and narrows the bronchi. Often, bronchial walls collapse, choking off the vital flow of air. Air is also trapped within the bronchial walls. Weakened by enzymes, the walls of the alveoli rupture and blood vessels die. Lung tissue is replaced with scar tissue, leaving areas of destroyed alveoli that appear as "holes" on an X-ray. Small areas of destroyed alveoli are called blebs, and larger ones are called bullae.

As emphysema progresses, the patient develops a set of large, overexpanded lungs with a weakened and partially plugged bronchial tree subject to airway collapse and air trapping with blebs and bullae. Breathing, especially exhalation, becomes a slow and difficult process. The patient often develops a barrel chest. The scientific world calls the mismatching of breathing to blood distribution a ventilation-to-perfusion imbalance; that is, when air arrives in the alveolus, there are no blood vessels there to transport the vital gaseous cargo to the cells (as a result of enzymatic damage). A person with COPD has a bronchial tree with a narrow, defective trunk (chronic bronchitis) and sparse leaves (emphysema).

The loss of elasticity of the lung and alveoli is a critical problem in the patient with emphysema. About one-half of the lungs’ elastic recoil force comes from surface tension. The other half comes from the elastic nature of certain fibers throughout the lungs’ structure. Emphysema weakens both of these forces because it destroys the elastic fibers and interferes with the surface tension. Fluid, a saline solution, bathes all the body’s cells and surfaces. In the lung, this fluid contains a surfactant, a substance that interferes with water’s tendency to form a spherical drop with a pull into its center (and ultimate collapse). The tissue that gives shape to the lungs is composed of specialized fibers that contain a protein called elastin. These elastic fibers are also found in the alveolar walls and in the elastic connective tissue of the airways and air sacs. The amount of elastin in lung tissue determines its behavior. Healthy lungs maintain a proper balance between destruction of elastin and renewal. (Other parts of the body, such as bones, do this as well.) If too little elastin is destroyed, the lungs have difficulty expanding. If too much is destroyed, the lungs overexpand and cannot recoil properly.

The process of elastin destruction and renewal involves complex regulation. Specialized lung cells produce new elastin protein. Others produce elastase, an enzyme that destroys elastin. The liver plays a role in the production of a special enzyme known as alpha-1-antitrypsin, which controls the amount of elastase so that too much elastin is not digested. In emphysema, these regulatory systems fail: Too much elastin is destroyed because elastase production is no longer controlled, apparently because alpha-1-antitrypsin production has been reduced to a trickle. In some persons, alpha-1-antitrypsin deficiency is an inherited condition.

The loss of elastin (and thus elastic recoil) means that the lungs expand beyond the normal range during inspiration and cannot resume their resting size during expiration. Thus, alveoli overinflate and rupture. This further reduces elasticity, because the loss of each alveolus further impairs the surface tension contribution to the lungs’ ability to recoil. Thus, a state of hyperinflation is assumed in the patient with emphysema. This leads to stretched and narrowed alveolar capillaries, loss of elastic tissue, and dissolution of alveolar walls. The lungs increase in size, the thoracic (chest) cage assumes the inspiratory position, and the diaphragm becomes low and flat instead of convex. The patient becomes short of breath with any type of exertion. As the disease worsens, the patient’s skin takes on a cyanotic (bluish) color as a result of poor oxygenation and perfusion. Wheezing is often present, and coughing is difficult and tiring. In the worst cases, even talking is enough exertion to produce a spasmodic cough. The hyperinflated chest causes inspiration to become a major effort, and the entire chest cage lifts up, resulting in considerable strain.

Emphysema may be diagnosed by the early symptom of dyspnea (shortness of breath) on exertion. In advanced cases, the distended chest, depressed diaphragm, increased blood carbon dioxide content, and severe dyspnea clearly point to the disease.

Treatment and Therapy

The initial step in treating emphysema is to eliminate the causes of irritation: smoke, polluted air, infection, and allergies. For smokers, smoking cessation is critical, and bupropion may be prescribed to help with smoking cessation. To improve dyspnea and the patient's quality of life, pulmonary rehabilitation may be part of the treatment process, including exercise training, nutrition counseling, and patient education. Exercise training may include exercises to strengthen the chest muscles as well as breathing techniques to improve air flow into the lungs.

A number of medications are useful in the treatment of emphysema, although no medications have been shown to modify the long-term decline in lung function seen in patients with emphysema or COPD. Instead, medications are used to decrease symptoms and reduce complications. Bronchodilator drugs relieve bronchospasms, reduce wheezing and dyspnea, and improve respiratory muscle function. Categories of bronchodilators include the beta-2 agonists, which may be short-acting or long-acting, and inhaled anticholinergics. Examples of short-acting beta-2 agonists include albuterol, terbutaline, fenoterol, and levalbuterol. Among the long-acting beta-agonists are arformoterol and formoterol. Some side effects of beta-agonists include nervousness, headache, nausea, and muscle cramps. Inhaled corticosteroids may also be used in the treatment of emphysema; however, the long-term use of corticosteroids may increase the risk of pneumonia.

Antibiotics are sometimes prescribed for patients with emphysema to combat bacterial infections that can dramatically worsen the effects of their condition. Furthermore, the influenza vaccine and pneumococcal polysaccharide vaccine are strongly recommended to reduce serious illness and complications.

Sometimes emphysema patients are given supplemental oxygen, also called oxygen therapy, if their lung function is too impaired to keep the oxygen levels in their blood sufficiently high. Portable oxygen tanks that deliver oxygen through a tube and a mask can give patients greater mobility to carry out tasks of daily living. In rare cases, lung surgery is an option for severe cases of emphysema. The two kinds of surgery available are lung volume reduction surgery (LVRS) and, as a last resort, a lung transplant. The aim of LVRS is to remove the most diseased portions of the lung to give the healthier portion more room to function. A lung transplant may be considered if a patient's lungs are in danger of failing entirely and if the patient is determined to be strong enough to endure the procedure and the recovery period.

Individuals with emphysema should avoid both excessive heat and excessive cold. If body temperature rises above normal, the heart works faster, as do the lungs. Excessive cold stresses the body to maintain its normal temperature. Smog, air pollution, dusts, powders, and hairspray should be avoided. Finally, a healthy diet consisting of foods high in calcium, vitamins, complex carbohydrates, proteins, and fiber is advised for the patient with lung disease. Caloric supplementation may improve exercise capacity in patients with COPD, especially undernourished patients.

Perspective and Prospects

According to the US Centers for Disease Control and Prevention (CDC), chronic lower respiratory diseases (primarily COPD) were the third leading cause of death in the United States in 2011. The World Health Organization reported in 2014 that COPD was also the third leading cause of death worldwide, accounting for 3.23 million deaths in 2019. Aside from death, a disease such as emphysema can cause long years of disability, joblessness, loss of income, depression, hospitalization, and an inability to perform normal activities.

Smoking is, by far, the single most important risk factor for emphysema. The prevalence of COPD among smokers is estimated to be approximately 15 percent. Socioeconomic status also influences rates of COPD, with lower-income workers experiencing higher rates of the disease. Over 90 percent of those who die from COPD complications are in low- or middle-income countries, as ineffective health care systems in many such areas exacerbate the disease and its progression. The prevalence of COPD also increases with age.

A number of economic pressures are likely to move COPD treatment from the hospital to the home. When effectively carried out by a well-trained health team, home care can lower medical costs. The COPD patient who finds a knowledgeable doctor and who begins a comprehensive rehabilitation program is the one who can look forward to a life that is more productive and more comfortable.

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