Effect of Vehicular Particulate Matter on the Lung Function of Asthmatic Children in Fresno, CA Jamie Mikkelsen Abstract Exposure to particulate matter (PM) is associated with adverse respiratory health effects. Vehicles traveling along a highway represent a significant source of fine particulates that contribute to the aggravation and possibly to the development of asthma in children. Residential history information and lung function data from 89 children involved in the Fresno Asthmatic Children’s Environment Study were used to quantify the impact of PM exposure from vehicles on lung health. The forced expiratory flow volume in one second (FEV1) was collected for each child using a spirometer during office visits between November 2000 and December 2001. Individual-level demographic and socioeconomic data as well as the exact locations of the children’s residences were gathered during home interviews. Residential address data were incorporated into a geographic information system to determine the distances of each residence to the closest highway in Fresno, CA. The distances to only highway 99 were also calculated. The categorical distances reported by the study participants were also used to estimate exposure to vehicular PM. Using three stepwise linear regression models, the effects of proximity to a vehicular source of PM on the mean FEV1 values were evaluated. After adjustment for sex, household income level, race, standing height, parental smoking, mother smoking during pregnancy, time lived in residence, and time of FEV1 test, the measures of absolute distances to the highways were found to be insignificant in predicting changes in mean FEV1 values. The regression model using self-reported distance variables indicated that children who lived one to three blocks from the source of vehicular PM experienced a 10% increased in mean FEV1 values, as compared to children who resided immediately next to the pollution source. These results indicate that living in an area with high traffic density may negatively affect the lung function of children with asthma.Introduction The number of childhood asthma cases in the United States has increased dramatically in recent years. Current estimates indicate that 4.4 million children in the United States under 18 years old suffer from the respiratory problem (Centers for Disease Control 1996). Asthma is defined by sporadic respiratory symptoms, such as wheezing and coughing, and airway hyperresponsiveness (Balmes 1993). The severity of asthma can range from mild symptoms to life-threatening episodes. Complex combinations of factors contribute to the onset of asthma. There is strong evidence from epidemiological studies, however, that identifies air pollution as an aggravator of respiratory problems in urban areas. Prolonged exposures to an inflammatory agent, like particulate matter (PM), can result in chronic bronchial problems (Taggart et al. 1996, Rosas et al. 1998, Cassino et al. 1999, English et al. 1999). Lipsett et al (1997) found a positive association between emergency room visits and ambient levels of PM less than 2.5 µm in diameter. Continued investigations of the respiratory health effects from PM exposure are necessary in order to predict the risk factors that may cause an asthmatic response (Stone 2000). Research has confirmed the effects of air pollution on respiratory function of adults, however, current studies are focusing on the factors contributing to impaired lung function in children. Children are more susceptible to the damaging effects of air pollution for many reasons. Their higher levels of outdoor activity, as compared to adults, increases their exposure to harmful pollutants (Stone 2000). A Southern California study found children to have a greater response to air pollution than adults (McConnell et al. 1999). In addition, children’s lungs are still developing which makes them more vulnerable to impairment (Bates 1995). Studies on children are particularly important because polluted childhood environments can lead to decreased adult lung function. Recently, a few studies have looked at the link between PM exposure and childhood asthma. A study in Switzerland found an increased relative risk of asthma incidence of 1.16 for a 20 µg/m3 increase in exposure to total suspended PM (Braun-Fahrlander et al 1992). Children in one study were more likely to develop coughs and other respiratory symptoms as a result of prolonged exposure to suspended particulates (Schwartz et al 1994). Proximity to industrial activity and roadways has been identified as a risk factor for the exacerbation of asthma (Stone 2000). Studies have shown a link between exposure to PM from vehicle exhaust and an increase in asthma symptoms in children. Research conducted in the United Kingdom found that children admitted to a hospital for respiratory problems were morelikely to live within 500 meters of a main road with high traffic density (Edwards 1994). Another study found a positive relationship between self-reported asthmatic symptoms and traffic density in children in Germany (Duhme 1996). Recent studies indicate that children living near a vehicular source of PM experienced decreases in their lung functions (Brunekreef et al 1997 van Vliet et al 1997). However, some studies have not controlled for individual level confounders, such as socioeconomic factors or the time a child has lived near a source of PM, which could possibly confound the results. The city of Fresno, California was an ideal study site for the analysis of the link between exposure to vehicular PM and lung function in children. There was a high incidence of asthma among the inhabitants of Fresno and the level of PM in the ambient air has consistently exceeded state and federal air quality standards; for the past 12 years, the highest annual geometric mean at the monitoring sites within Fresno County was above the State of California’s annual standard for PM less than 10 µm in diameter (California Air Resources Board 1999). Highway 99, a freeway used heavily by trucks and passenger vehicles, runs through residential areas of Fresno. Three other freeways, highways 41, 168, and 180 traverse the city. Researchers for the Fresno Asthmatic Children’s Environmental Study (FACES) initiated a five-year cohort study to identify the possible environmental factors that influence the natural history of asthma. The study began in November
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