Short term effects of outdoor air pollution on respiratory health in susceptible populations.

摘要

The main objective of this dissertation was to improve the current understanding of acute effects of outdoor air pollution on respiratory health in two potentially susceptible groups, elderly individuals with chronic obstructive pulmonary disease (COPD) and children with and without asthma. In order to address this objective, the following specific aims were completed: 1) complete a systematic literature review and meta-analysis evaluating the association between outdoor air pollution and COPD-related emergency department visits, hospitalizations and mortality, 2) quantify the association between risk of COPD exacerbation and measures of outdoor air pollution derived from central monitors, using data from a case-crossover study of COPD patients enrolled in a disease management group, and 3) quantify the association between exhaled nitric oxide (eNO; a measure of airway inflammation) and measures of outdoor air pollution derived at central site monitors among asthmatic and non-asthmatic sibling pairs, using data from a prospective cohort study with repeated eNO measurements.;Results of Aim 1: This study found that short-term exposures (up to a maximum of seven days) to particulate matter (PM2.5), nitrogen dioxide (NO2), and sulfur dioxide (SO2) were associated with increased risk of COPD-related emergency department visits (ED) and hospitalizations (HA). We estimated a 2.6% (1.4%-3.8%) increased risk of COPD-related ED-HA for a 10 microgram per cubic meter (ug/m3) increase in PM 2.5, a 4.4% (1.4%-3.8%) increased risk of COPD-related ED-HA for 10 ug/m3 increase in NO2, and a 2.5% (0.5%-4.5%) increased risk of COPD-related ED-HA per 10 ug/m3 increase in SO 2. This study also found that the strength of the summary effect estimates was somewhat dependent on the selected lag or averaging time between exposure and outcome, as well as the outcome definition. These differential risk estimates highlight the implications that certain decisions/selections can have on summary effect estimates in meta-analyses and can be used to aid air quality policies and guide future research.;Results of Aim 2: Using data collected from case-crossover study, which included 168 patients with mild to very severe COPD residing in central Massachusetts, this study found a strong positive association between short-term exposures to low levels of outdoor SO2 and COPD exacerbation at concentrations far below the NAAQS (odds ratio (OR) = 2.28 (1.64-3.19)); the association was even stronger when adjusted for PM2.5 (OR=2.45 (1.75-3.45)). This research also found a non-significant positive association between NO2 and COPD exacerbation (OR=1.06 (0.98-1.16)) and a non-significant negative association between PM2.5 and COPD exacerbation (OR = 0.94 (0.88-1.01)). These results are inconsistent with existing literature and highlight the complexities of modeling air pollutants with a high degree of temporal variability that correlate with one other and with meteorological variables differently across space and through time.;Results of Aim 3: Using data collected from a prospective cohort study on 70 discordant sibling pairs (where one child had received a doctor diagnosis of asthma and the other had not) residing in central Massachusetts, this study estimated a statistically significant 2.1% increase in eNO per 1 part per billion (ppb) increase in NO2, independent of asthmatic status. This study also estimated a 6.7% decrease in eNO per 1ppb increase in SO 2, which was strengthened upon adjustment by both NO2 and PM2.5 and a null association between PM2.5 and eNO (0.10% increase). The results for NO2 are consistent with existing literature while the results for PM2.5 are not. There is little information in the existing literature regarding the association between SO2 and eNO. Further study is needed to better understand these results and the utility of eNO as a biomarker to measure airway inflammation from short-term exposures to low levels of outdoor air pollution, particularly when quantifying exposure from central monitors.;Conclusions: The results from these three studies suggest, above all, that further study is needed to better understand the complex relationships between pollutants and the implications that these have for epidemiologic studies. These findings also indicate that the current NAAQS' may not be adequately protective of the more vulnerable members of our population. Finally, these findings suggest that the current single pollutant framework used to regulate air pollution in United States may not effectively protect human health from the additive or multiplicative effects of exposures to multiple pollutants.