Respiratory Diseases | Research & Encyclopedia Articles

Respiratory diseases—diseases of the lungs and airways such as asthma, chronic bronchitis, emphysema, and lung can cer—have diverse causes. While cigarette smoking is the leading cause of most major respiratory diseases, air pollutants and workplace toxins can also contribute to respiratory illness.

The lungs are equipped with an elaborate defense system to repel toxins and invading organisms. Before air reaches the lungs, it passes through the nose, throat, and bronchi that are lined with mucus to trap irritants. Within the bronchi, smaller bronchial tubes and bronchioles are covered with cilia that sweep particles out. Lungs are far from vulnerable, however. The defenses can fail, leading to any number of respiratory diseases.

Cigarette smoking is the most important cause of Chronic Obstructive Pulmonary Disease (COPD), a name covering pulmonary emphysema and chronic bronchitis. These lung diseases damage the air passageways and interfere with the lung's ability to function. COPD is the fifth leading cause of death in the United States, and in a smoking, aging population, will probably not decline.

Chronic bronchitis is a persistent inflammation of the bronchial tubes. Mucus cells of the bronchial tree produce excess mucus, and the lungs may become permanently filled with fluid. Eventually, scar tissue from infection replaces the cilia, decreasing the lungs' efficiency. With each infection, mucus clogs the alveoli, or air sacs. Little or no gas exchange occurs, and the ventilation-blood flow imbalance reduces oxygen levels and raises carbon dioxide levels in the blood.

Chronic bronchitis usually accompanies the development of emphysema. The destruction of too many elastic fibers in the lungs' framework and air sac walls results in hyperinflated air sacs that impair the lungs' ability to recoil during expiration. Eventually, the alveoli merge into one large air sac, and the network of capillaries in the lungs is lost. This reduces gas exchange that occurs, and stale air is trapped in the lungs.

These two COPDs are not curable, but can be treated. Patients can prevent pulmonary infections and the inhalation of harmful substances, reduce airway obstruction, improve muscle conditioning and use supplemental oxygen.

Asthma is a disease characterized by a narrowing of the airways, episodic wheezing, tightness in the chest, shortness of breath, and coughing. There are various types of asthma, including exercise-induced asthma, occupational asthma triggered by irritants in the workplace, and asthmatic bronchitis. Trigger factors can include dust, odors, cold air, sulfur dioxide fumes, emotional stress, upper-respiratory infection, exertion, and airborne allergens. Asthma is often preventable if trigger factors can be identified and eliminated.

Scientists are also turning their attention to health hazards posed by atmospheric acids and other air pollutants. One study at 79 southern Ontario hospitals showed a consistent association between the summer levels of atmospheric sulfates and ozone and hospital admissions for acute respiratory illnesses such as asthma, chronic bronchitis, and emphysema.

This "acid air" forms when emissions of sulfur dioxide and nitrogen oxides, mostly from coal-burning power plants and motor vehicles, are transformed to sulfuric and nitric acids. Acid aerosol concentrations tend to be higher on hot summer days. The fine acid particles can penetrate the deepest, most delicate tissues of the lungs, inflame respiratory-tract tissue, depress pulmonary function, and constrict air passages. Health effects are more pronounced when acid aerosols are accompanied by ozone in the lower atmosphere. Together, ozone and acid aerosols produce changes in the lungs that inhibit their ability to clear themselves of toxins and other irritants.

High levels of air pollution may foster respiratory-disease symptoms in otherwise healthy individuals. One study indicates that air pollution in Los Angeles may begin to permanently "derange" an individual's lung cellular architecture by age 14. Another study has implicated wood-burning stoves, which foul the air with tiny particulates that may cause or exacerbate outbreaks of respiratory illnesses. An environmental team studying respiratory problems at a Boston-area high school implicated the school's poorly designed ventilation system as the most likely cause of the students' high rate of respiratory illnesses.

Workplace-related respiratory diseases are on the increase. In 1990, the National Safety Council listed occupational lung diseases as the leading work-related diseases in this country. The Chicago-based National Safe Workplace Institute recently concluded that 2–4% of pulmonary disease is related to working conditions. Diseases that top the list include asbestosis, lung cancer, silicosis, occupational asthma, and coal workers' pneumoconiosis, commonly known as black lung disease.

Asbestosis is a chronic fibrotic lung disease caused by the inhalation of inert dusts. This affliction has received widespread media coverage because the majority of its victims have been subjected to long-term exposure to asbestos. Asbestosis causes a scarring of lung tissue that can result in serious shortness of breath. Silicosis is a disease of the lungs caused by breathing in dust that contains silica. Black lung disease is a long-term lung disease caused by the settlement of coal dust on the lungs, eventually resulting in emphysema.

Insurance data indicates that people in certain high-risk occupations, including agriculture, construction, mining, and quarrying have three to four times the average death rate for all industries, mostly from respiratory diseases.

Residential homes are also vulnerable. Chlorine bleach and cleaning fluids, insecticides, wood-burning fireplaces, and gas stoves that produce nitrogen dioxide can be toxic to the lungs. The causes of the expected 170,000 new cases of lung cancer in 1993 include exposure to cigarette smoke, ionizing radiation, heavy metals, and industrial carcinogens.

Air Quality; Automobile Emissions; Fibrosis; Respiration; Sick Building Syndrome; Smog; Smoke; Yokkaichi Asthma

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