COPD pathophysiology is a term used to describe the functional changes that occur inside the lungs as a result of the disease process. In order to better understand the lung abnormalities that are present in COPD, let's first familiarize ourselves with normal lung functioning.
How Our Lungs Work
The chest cavity contains two lungs: one on the right side of the chest and one on the left side. Each lung is composed of different sections called lobes. The right lung has three lobes; the left only two. Each lobe is further divided into segments and lobules. The space between the lungs that contains the heart, great vessels and esophagus is called the mediastinum. A set of tubes, or airways, delivers oxygen to each section of the lung.
As we breathe, air enters our respiratory system through our nares. It then passes through the nasopharynx (area of throat behind nose) and the oropharynx (area of throat behind mouth). These structures make up the upper airways, which are lined with ciliated mucosa: a protective, moist tissue layer containing tiny hair-like projections that help warm and humidify inhaled oxygen and assist in the removal of foreign particles and excess mucus. Air continues on through the larynx (voice-box) -- a structure that connects the upper and lower airways -- and then down through the trachea (windpipe), which connects the larynx to the bronchi. The bronchi are larger airways of the lungs which subsequently terminate into smaller airways called bronchioles. Together, the bronchi and bronchioles make up the bronchial tree. The bronchioles end in alveolar ducts, which lead to alveolar sacs made up of millions of alveoli. The alveoli are the primary, gas-exchanging structures in the lungs, where oxygen enters the blood and carbon dioxide is removed. To learn more about how your lungs function, take a tour of the respiratory system.
The Purpose of the Lungs
The lungs are made up of spongy, elastic fibers that allow them to stretch and constrict when we breathe in and out, respectively. The purpose of the lungs is twofold: to deliver oxygen (O2) to the cells and tissues of the body and to remove carbon dioxide (CO2), the waste product of respiration, from the blood. Oxygen, the body's most important nutrient, helps our bodies turn the food that we eat into energy and, similar to car exhaust, CO2 is removed from our bodies every time we exhale.
Understanding COPD Pathophysiology
COPD is characterized by airflow limitation that is poorly reversible. Cumulative, chronic exposure to cigarette smoking is the number one cause of the disease, but repeated exposure to secondhand smoke, air pollution and occupational exposure (to coal, cotton, grain) are also important risk factors.
Chronic inflammation plays a major role in COPD pathophysiology. Smoking and other airway irritants cause neutrophils, T-lymphocytes, and other inflammatory cells to accumulate in the airways. Once activated, they trigger an inflammatory response in which an influx of molecules, known as inflammatory mediators, navigate to the site in an attempt to destroy and remove inhaled foreign debris.
Under normal circumstances, the inflammatory response is useful and leads to healing. In fact, without it, the body would never recover from injury. In COPD, repeated exposure to airway irritants perpetuates an ongoing inflammatory response that never seems to shut itself off. Over time, this process causes structural and physiological lung changes that get progressively worse.
As inflammation continues, the airways constrict, becoming excessively narrow and swollen. This leads to excess mucus production and poorly functioning cilia, a combination that makes airway clearance especially difficult. When people with COPD can't clear their secretions, they develop the hallmark symptoms of COPD, including a chronic, productive cough, wheezing and dyspnea. Finally, the build-up of mucus attracts a host of bacteria that thrive and multiply in the warm, moist environment of the airway and lungs. The end result is further inflammation, the formation of diverticula (pouch-like sacs) in the bronchial tree, and bacterial lung infection, a common cause of COPD exacerbation.
A Word About COPD Treatment
No other factor carries more weight in slowing the progression of COPD than smoking cessation. Other treatment options include antibiotics (for those with evidence of bacterial infection), inhaled bronchodilators, corticosteroids, aerosol therapy, pulmonary rehabilitation, oxygen therapy (for patients who are hypoxic), flu shots, and, in those suffering from end-stage COPD who meet specific criteria, surgical intervention.
Still unclear about COPD pathophysiology? Be sure to watch the following videos:
Hunter, Melissa, M.D, King, Dana, M.D. COPD: Management of Acute Exacerbations and Chronic Stable Disease American Family Physician. 2001, August 15.