Longitudinal Study on the Acute Effects of Ambient Air Pollution in Congestive Heart Failure PDF Download

Author: Stéphane Buteau
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Languages : en
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"People suffering from congestive heart failure (CHF) may be at higher risk for the acute effects of air pollution. The purpose of this dissertation was to investigate the acute effects of ambient air pollution in persons having CHF by making use of an innovative population-based longitudinal study design that can address limitations of previous epidemiological air pollution studies using grouped-analysis, notably by incorporating medical histories of subjects throughout the follow-up and spatially-resolved, time-dependent daily exposures to air pollution at subjects' residence.This dissertation includes three original studies: The first study is a structured review of panel studies that investigated the effect of ambient air pollutants (PM2.5, NO2, O3) on selected indices of HRV that reflect the activity of the autonomic nervous system, one important postulated mechanism linking air pollution and acute health events. Many of the 33 selected studies differed substantially in terms of design characteristics and statistical methodologies, thus limiting the possibility of pooling studies. I was not persuaded by the results that there was an association between PM2.5 and any of the four indices of HRV investigated, whereas for NO2 and O3 the number of high-quality studies was insufficient to draw definite conclusions. Panel studies with improved designs and methodologies are needed to establish or refute an association between ambient exposure to air pollution and HRV.The second study presents the development and comparison of spatially-resolved daily concentrations of NO2 and O3 predicted for areas defined by the first three-character of the postal codes in Montreal, 1991-2003, using different spatiotemporal models. For both pollutants, the results showed that the method used may lead to substantial differences in the daily mean concentrations assigned to a postal code area on a given day. The back-extrapolation method, which was the only method incorporating data from dense exposure surveys, showed a higher degree of disagreement with the other methods that were all constrained by the sparse monitoring network. In view of these substantial differences, the analyses of the health effects from air pollution should make use of multiple exposure models.The third study is a longitudinal cohort study, developed from administrative health databases, in elderly having CHF in Montreal, 1991-2003, to estimate: 1) whether non-accidental mortality was associated with spatially-resolved, daily exposures to ambient NO2 and O3, and; 2) whether these associations were modified according to a complication or worsening in a person's health. I used two distinct statistical designs: a case-crossover that contrasts the same person at different times, and a nested case-control that contrasts different persons at similar times. The effects of air pollution and weather on mortality were modelled using distributed lag nonlinear models over lags 0-3 days. I found that the estimates of risk depended on the exposure method and the statistical design used. Using the back-extrapolation method, which likely provide the better estimates of exposure, for the case-crossover the cumulative mean percentage changes (MPC) in daily mortality per interquartile increment in NO2 (8.8 ppb) was 3.0% (95% CI: -0.4, 6.6%) and for O3 (16.5 ppb) 3.5% (95% CI: -4.5%, 12.1%). For the nested case-control, the cumulative MPC in daily mortality was 2.9 % (95% CI: -0.9%, 6.9%) for NO2 and 7.3% (95% CI: 3.0%, 11.9%) for O3. In the nested case-control, but not in the case-crossover, I found evidence of effect modification according to the prescribed dose of furosemide, which is a diuretic used to treat CHF. This study strengthens the evidence that daily exposure to air pollution may increase the risk of daily mortality in CHF. The unique design and modeling framework illustrated in this study can form the basis of future investigations on the acute effects of air pollution. " --