Imagine most of the people of an entire city coughing and wheezing, gasping for breath, unable to do anything except cough. Think about older people dying of exhaustion from the effort to breathe. Think about infants and small children with blue-tinged skin and lips, rolling and tossing with discomfort as they, too, struggle to breathe. Imagine air that feels thick enough to eat like soup, air that never seems to satisfy the need to breathe. This has happened over the years in many cities all over the world. The cause: air pollution.
Air pollution is a significant cause of asthma. Polluted air is air that contains any substance harmful to health. These can be gases such as sulfur dioxide, chemicals such as formaldehyde, or tiny bits and pieces of solid matter that float in the air. Most air pollution is man-made, but there are some pollutants, such as volcanic gases and debris, that occur from natural causes. Although some fires are man-made, a major natural cause of air pollution is forest fires that are most often caused by lightning. Burning of thousands of acres of woodland contributes to pollution by ash, gases, and tiny particles of other materials made airborne by air currents from the fire. These materials are very irritating to the mucous membranes of the respiratory tract and can trigger asthma, especially in people with twitchy lungs.
Some problems of air pollution are related to allergies. Airborne pollens and many other allergens (substances that cause allergy), such as those of the ragweed plant, can cause asthma when they trigger a reaction with an antibody that results in release of mediator substances, which in turn stimulate spasm of the bronchial tubes, the benchmark of asthma. But not all of the asthma-causing materials in the air make trouble by provoking an allergy process. For example, sulfur dioxide (S02) particles, suspended in air in microscopic water droplets, are irritating enough to cause bronchospasm in nonalleigic patients. Only about half of the people troubled by air pollution have allergies; the other half wheeze because of the irritation these toxic materials cause. Another example is nitrogen dioxide (N02), which, like ozone, can cause either long-term or immediate problems or both.
Most troublemakers found in the air cause trouble by irritation. In most cases, the air pollutant simply irritates the mucous membranes along the path air takes into the lungs (the airway). That irritation causes inflammation; the inflammation causes asthma. Asthma produced this way doesn’t look any different from asthma caused by allergies and it responds to the same medical treatment. Asthma caused by air pollution is more serious than other types of asthma because, while asthma caused by an allergy may not cause symptoms following each exposure, asthma from pollution will occur with every exposure to the specific pollutant.
In some cases, the exposure to the irritant is so severe as to make an entire community sick. This has happened repeatedly in places as diverse as New Orleans; Buffalo; Yokohama, Japan; Birmingham, England; and Cartagena, Columbia. In 1948, 20 people died of asthma caused by “fog” in Donora, Pennsylvania. In 1952, there were 4000 deaths in London related to air pollution- To a lesser extent; asthma from air pollution has been a problem in all major industrial areas. The worse the pollution, the greater the number of people attacked and the more serious the illness in each patient. In many places, there is an increase in hospital admissions for asthma and pneumonia that coincides with increase in air pollution.
Reports of epidemic asthma continue to surface. One hundred forty-eight people in London were stricken with asthma on June 24-25 of 1994 when there was a sudden drop of air temperature and high pollution with grass pollen, as reported in the British Medical Journal of March 1996. Doctors in Barcelona found that epidemics of asthma occurred where soybeans were unloaded from silos, according to a report in Thorax, September 1994. Like other members of the legume group, which includes peas, beans, and peanuts, soybean has often been reported as a cause of allergic asthma. Antibodies that trigger allergic reactions to soybean protein can be detected in the blood of soy-sensitive patients.
An unusual epidemic of fatal asthma was reported from New Zealand in the mid- 1970s, and described in the International Archives of Allergy and Applied Immunology of May-June 1955. The report associated a rise in asthma deaths with the introduction of an asthma medicine into general use. When government order eliminated the drug from general usage, there was a sudden and marked reduction in the epidemic.8 Occurrences of epidemic asthma are unusual, but studying them provides much helpful data for doctors who manage the disease.
“I seem to get asthma more often than my big sister’
This quote from a 6-year-old about her 12-year-old sister suggests an age factor in the asthma world. Because the lungs of children are more likely to react to air pollution than the lungs of adults, children are the subject of much of the investigation of effects of air pollution on the lungs. Increased reaction of children’s lungs can easily be explained: Younger children have smaller bronchial tubes than older children and adults and thus a small decrease in the size of a child’s air passage causes much more difficulty than a small airway decrease in an older lung. So children are especially vulnerable to air pollution. But air pollution that troubles the breathing of children early on will also harm adults a little while later.
Some very common substances can add to air pollution. Materials that are disposed of by burning are a major problem. Burning wood or coal, even paper, can cause serious pollution and illness. One interesting asthma problem is called “meat wrappers’” asthma. Butchers cut meat and sometimes package it in plastic. Then, to seal the package, the plastic is heated until it melts and fuses. Melting plastic gives off fumes that cause some butchers to wheeze, hence the name given to this type of asthma.
Besides the common air pollutants, other substances can be toxic. Formaldehyde, used to manufacture home insulation, can be a problem. In new homes, formaldehyde can leak out of the insulation for months, even years, causing sudden episodes of asthma and long-term lung disease.
Other chemical offenders: TMA (tri-mellitic anhydride) and TDI (toluene diisocyanate), used to make plastics, are given off in manufacturing, during use, or on burning for disposal. Certain exposures in manufacturing are severe but not frequent causes of asthma. These include salts of platinum, chromium, and nickel, wood dusts, particularly cedar wood dust, and wheat and flour dust in industry and in bakeries. There are many things in the air, which we will not discuss here, that do not cause breathing problems but are harmful in other ways.
In the past 20 years, there has been a significant decrease in air pollution as a result of government regulation of auto exhaust and the switch to unleaded gasoline. Sulfur dioxide, not released in auto exhaust, is a useful index of air pollution. The amount of S02 in the air is watched by scientists who track air pollution. An acceptable level of S02 is less than 0.14 part per million. There are acceptable levels also for carbon monoxide, nitrogen dioxide, and lead that can be tracked and sometimes appear along with local weather reports.
Small particles of anything can be a problem. Particles cause the blackness in “black smoke.” Absence of particles provides smoke that is dear or white, composed of harmless water vapor. Particulate matter can include pollen and dusts of all kinds, bits of unburned coal or other fuel source, tiny bits of paper or plastic, chemicals, in fact, anything that is small enough to float in the air.
One air pollutant requiring careful consideration is tobacco smoke, which has been proven to cause an increase in cancer deaths and severe damage to the lungs of smokers. In persons with allergies, cigarettes may activate asthma. There is also evidence that smoking causes asthma in people who do not themselves smoke but who inhale smoke from people who do. This “secondhand” smoke is a serious problem within families. There is a higher incidence of asthma in the children and families of smokers than nonsmokers. The more smokers in the family, the worse the problem is. Asthma is also a problem in adults who spend too much time in smoke-filled rooms. As with air pollution in general, exposure to cigarette smoke is gradually being turned off by legislation requiring smoke-free rooms and smoking and nonsmoking areas. Smoking marijuana causes serious irritation as well.
Interestingly, pipe smoke is less troublesome for the smoker than are cigarettes. Pipe smoke is inhaled after passage through the pipe during which time the temperature of the smoke drops to the point at which many of the harmful pollutants drop out of the smoke.
Preventing asthma that is caused by other kinds of air pollution is not easy. The first step, identifying the cause, may require professional help by someone knowledgeable in the many and sometimes subtle causes of air pollution. Avoiding the identified pollutant is the next step. This can mean changing geographic location, use of a face mask for short-term exposures, arid air purification equipment for long-term exposure. Management should be tailored to the individual problem. For example, using a mask when vacuuming or gardening is easy; moving to another geographic area is not. Simply being aware of the how air pollution relates to asthma is a big step in the right direction.
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