Chronic obstructive pulmonary disease (COPD) is a term used to describe two separate, but inter-related processes: emphysema and chronic bronchitis. These two conditions often co-exist in the same individual, and when they do the patient is diagnosed with COPD. Chronic obstructive pulmonary disease is usually caused by years of cigarette smoking; however, other less common causes exist. It is a common cause of lung morbidity and mortality in the United States.
The lung is composed of air conducting tubes known as bronchi. Each bronchi branches twelve times, ultimately giving rise to smaller tubes known as "bronchioles", which again branch repeatedly. After the 25th branch point, bronchioles are termed "respiratory bronchioles", which become alveolar ducts. Branching off of the alveolar ducts are alveoli, the site of gas exchange in the lung.
Emphysema, one of the components of COPD, is a process in which the airspaces from the respiratory bronchiole onward become abnormally enlarged. In addition, the walls of these airspaces are damaged resulting in decreased gas exchange capability. The damage is believed to be caused by inflammation. More specifically, white blood cells known as neutrophils (aka: polymorphonuclear cells or "polys") release an enzyme called elastase. Elastase chews up lung tissue.
Interestingly, elastase is normally inhibited by a protein known as α-1 antitrypsin, which is produced by the liver. Chemicals in cigarette smoke inhibit the activity of α-1 antitrypsin allowing elastase to wreak havoc on lung tissue. Some unlucky individuals also have genetic defects in α-1 antitrypsin and can develop emphysema without a history of smoking (talk about bad luck!).
The second component of COPD, chronic bronchitis, occurs when inhaled substances (think of cigarette smoke, dusts, etc.) repeatedly irritate the lining of the bronchi. The bronchi try to protect themselves by increasing the number of mucous secreting cells (ie: goblet cells). In addition, white blood cells are recruited to the walls of the bronchi with resultant inflammation and scarring.
Both emphysema and chronic bronchitis cause airway obstruction. The inflammation that occurs causes narrowing of the small air tubes (bronchioles), which causes air to get trapped in the lungs.
The symptoms of chronic obstructive pulmonary disease depend on which of the two pathologies, emphysema or chronic bronchitis, is most predominant. If patients have severe emphysema they are often short of breath (ie: dyspnea), have a large chest (ie: "barrel chested"), exhale longer than normal, and often breathe through pursed lips to increase their airway pressures (this allows them to force more of the trapped air out during exhalation).
COPD can take its toll not only on the lungs, but also on the rest of the body. It is not uncommon for patients with this disease to lose muscle and weight. Patients with chronic obstructive pulmonary disease are also at increased risk of bone fractures because of osteoporosis. Some patients can become clinically depressed as well.
Ultimately patients with COPD often have a mixture of symptoms from both emphysema and chronic bronchitis. This can make distinguishing between the two pathologies difficult, it not impossible.
Diagnosis of chronic obstructive pulmonary disease is based on clinical history and ancillary testing. To diagnose chronic bronchitis patients must complain of a productive cough for at least 3 months out of the year for a minimum of two years.
Chest X-rays can show the "barrel chest" that is often seen in patient's with this disorder. Pulmonary function testing is done to evaluate how well patients can exhale. Patients with COPD will show a decreased FEV1 (forced expiratory volume in 1 second) to FVC (forced vital capacity) ratio on pulmonary function testing. This means that the patient has a decreased ability to exhale as much of their maximum lung volume (FVC) as possible in one second (ie: "FEV1"). Any patient with an FEV1 < 80% predicted or an FEV1:FVC < 0.7 has evidence of obstructive lung disease. The Global Initiative for Chronic Obstructive Lung Disease (GOLD) further classifies how severe the patient's COPD is based on how "bad" the FEV1 and FEV1:FVC measurements are.
Arterial blood gases are also commonly obtained to see how well oxygenated the blood is. The arterial blood in a patient with COPD will often have a decreased oxygen content compared to normal individuals. This is a result of oxygen not being able to diffuse from the alveoli into the blood stream.
Treatment of chronic obstructive pulmonary disease has two goals: improving quality of life, and reducing morbidity and mortality. Numerous medications exist to improve quality of life.
The first class of medications are the "bronchodilators". They exist in two flavors: β-agonists and anticholinergics. Inhaled β-agonists act by relaxing the smooth muscle that surrounds the bronchi, which allows them to "open up". Long acting β-agonists like salmeterol and formoterol are first line therapies to control symptoms in COPD. Other commonly used inhaled medications include the anticholinergics. They exist in short acting (ipratropium) and long acting formulations (tiotropium). There is some evidence that anticholinergic inhalers may be a better initial choice compared to long acting β-agonists for treating mild symptoms. Sometimes both β-agonists and anticholinergic inhalers may be needed concomitantly to control symptoms.
Patients who have worsening disease, or frequent COPD flairs may be started on inhaled corticosteroids, which can prevent future exacerbations. They should only be used in combination with a bronchodilator. It is important to note that long term use of inhaled steroids pose health risks such as worsening bone density, cataract formation, diabetes, and increased risk of infection.
Interestingly, the only medical treatment shown to improve survival in COPD is oxygen! Oxygen therapy is usually started when a resting arterial blood gas shows an oxygen pressure of less than 55 mmHg or when pulse oximetry (ie: that "little finger thingy") is less than or equal to 88%. However, if the patient also has evidence of right sided heart failure than oxygen may be started if the arterial oxygen pressure is between 56 and 59mmHg, or the pulse oximetry reading is less than 89%.
Surgical options also exist, and include lung reduction surgery and lung transplant. Generally these options are reserved for severe disease. Studies have shown that they may improve survival in select patients.
Finally patients should stop smoking and get yearly influenza vaccinations, as well as the pneumococcal vaccine.
Chronic obstructive pulmonary disease is a common cause of morbidity and mortality. It is most commonly seen after many years of cigarette use. It is a condition characterized by two inter-related, but distinct pathologies: emphysema and chronic bronchitis. Symptoms include shortness of breath, cough, and in severe cases a "wasted" appearance. Diagnostic studies should include a chest X-ray, pulmonary function testing, and arterial blood gas analysis. Treatment consists of inhaled bronchodilators. In more severe cases inhaled steroids, oxygen therapy, and lung reduction surgery may be appropriate.
(1) Celli BR. Update on the management of COPD. Chest. 2008 Jun;133(6):1451-62.
(2) Global Strategy for the diagnosis, management, and prevention of COPD; Global Initiative for Chronic Obstructive Lung Disease (GOLD). Copyright 2009, Medical Communications Resources, Inc.
(3) Berry CE, Wise RA. Mortality in COPD: causes, risk factors, and prevention. COPD. 2010 Oct;7(5):375-82.