Asthma diagnosis and treatment
The role of air pollution in asthma and other pediatric morbidities

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A growing body of research supports the role of outdoor air pollutants in acutely aggravating chronic diseases in children, and suggests that the pollutants may have a role in the development of these diseases. This article reviews the biologic basis of children's unique vulnerability to highly prevalent outdoor air pollutants, with a special focus on ozone, respirable particulate matter (PM2.5 [<2.5 μm in diameter] and PM10 [<10 μm in diameter]), lead, sulfur dioxide, carbon monoxide, and nitrogen oxides. We also summarize understanding regarding health effects and molecular mechanisms of action. Practitioners can significantly reduce morbidity in children and other vulnerable populations by advising families to minimize pollutant exposures to children with asthma, or at a broader level by educating policymakers about the need to act to reduce pollutant emissions. Management of children with asthma must expand beyond preventing exposures to agents that directly cause allergic reactions (and therefore can be diagnosed by means of skin tests) and must focus more attention on agents that cause a broad spectrum of nonspecific, generalized inflammation, such as air pollution.

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Sources and pathways of exposure

Outdoor air pollutants can come from many sources and include both gaseous and particulate pollution. Air pollution arises in 2 ways: as primary pollutants emitted directly out of exhaust pipes and stacks (including the gaseous pollutants NOx and SO2, as well as PM, such as soot), and as secondary pollutants formed from the primary pollutants in the atmosphere in the copresence of sunlight, moisture, or both (including O3 and secondary particles, such as sulfates). The dominant anthropogenic

Biologic bases for children's unique vulnerability to air pollution

Organogenesis of the lung begins in fetal life and is especially rapid in early childhood. The number of alveoli in the human lung increases from 24 million at birth to 257 million at the age of 4 years,4 and changes in the lung continue through adolescence.5 Exposure to air pollution alters the normal process of lung development, which is guided by a complex and precisely timed sequence of chemical messages.6 This suggests that air pollution might have a lasting effect on respiratory health.

The effects of individual pollutants on children's health

Air pollution episodes have provided the starkest evidence of their potential health consequences for children. A landmark event in the recognition of the disastrous effect of air pollution on child health occurred from December 1 through 5, 1952, in London. Trapped coal smoke in the Thames valley accumulated as a result of a stationary high-pressure cell accompanied by wind speeds near zero. Approximately 4000 excess deaths occurred in London that week,20 and excess deaths continued for weeks

Molecular mechanisms of air pollution toxicity

Exposure to outdoor air pollutants has been proven to induce molecular processes that could cause adverse fetal and perinatal outcomes. In one study, volunteers exposed to diesel particles for 1 hour had increases in peripheral white blood cell counts, as well as increased vascular cellular adhesion molecule 1 and intercellular adhesion molecule 1 levels in the lung epithelium. Increases in levels of C-reactive protein, an acute-phase inflammatory marker, have been associated with air pollution

Clinical implications

During the past 15 years, the incidence of asthma and the prevalence of severe asthma have increased in many countries, despite the availability of improved medications. A recent careful survey of schoolchildren in Hartford, Connecticut found that 19% had asthma.90 Some evidence suggests that air pollution might have contributed to the increasing prevalence of asthma.91, 92 Regardless of the role of air pollution as a contributing factor to the prevalence of asthma, the study by Gent et al24

Key steps for prevention of exposure

Infants and children are among the most susceptible to the important and diverse health effects of outdoor air pollution and provide a compelling need to move forward on efforts to ensure clean air for all. Currently, levels of O3 and PM air pollution remain unhealthy in many parts of the United States, and the current National Ambient Air Quality Standards might not protect the public adequately. The findings of Gent et al24 suggest that asthmatic children who use maintenance medication were

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    This work was supported by a Superfund Basic Research Program grant to the Mount Sinai School of Medicine (NIEHS P42 ES07384) and by an Environmental Health Sciences Center of Excellence grant to the New York University School of Medicine (NIEHS ES00260).

    Disclosure of potential conflicts of interest: L. Trasande—none disclosed. G.D. Thurston—none disclosed.

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