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The alignment of immediate health effects of multi-hour exposure periods
Citation:
Schneider, A., L. M. NEAS, R. W. WILLIAMS, M. W. CASE, A. Hinderliter, A. Peters, AND R. B. DEVLIN. The alignment of immediate health effects of multi-hour exposure periods. Presented at International Society for Environmental Epidemiology Annual Conference, Pasadena, CA, October 12 - 16, 2008.
Impact/Purpose:
research results
Description:
Objective: Exposure to [me airborne particulate matter (PM2.5) has been associated with cardiovascular outcomes, including acute effects on endothelial dysfunction. With such immediate effects, the choice ofthe exposure timeframe may be a critical factor. This analysis compares the effects of a marker of endothelial dysfunction within different exposure time windows. Methods: A prospective panel study was conducted on 22 adults with type-2 diabetes in Chapel Hill, NC, from Nov 2004-Dec 2005. Each subject was studied for 4 consecutive days. Brachial artery flow mediated dilatation (FMD) was measured by brachial artery ultrasound during each subject visit at around lOam. On the rooftop of the patient examination site, 24¬hour PM2.5 measurements were made from 9am to 9am. At an airport monitoring station (3.5 km north of the patient examination site), 24-hour PM2.5 measurements were conducted from midnight to midnight. FMD measurements were analyzed using random effects models adjusting for season, weekday and meteorology. Results are presented for an increase of 10Jlg/m3 PM2.5 as percent changes of mean FMD with a 95% confidence interval. We examined three exposure metrics on the day of the subject's visit: the rooftop measures starting at 9am, the rooftop measures ending at 9am, and the airport measures starting at midnight. Results: The correlation between the two rooftop exposure windows was only moderate (FO.54). The airport measures (midnight to midnight) were more highly correlated with the rooftop measures starting on the day of the subject's visit (FO.80) than with the rooftop measures ending on the day of the subject's visit (FO.69). FMD decreased by -17.3% [¬34.6%; 0.0%] inassociationwith airportPM2.5exposure startingatmidnightof theday ofthe subject's visit. The FMD association was stronger for the rooftop measures starting at 9am on the day of the subject's visit (-23.9% [-42.0%; -5.8%]) than for the rooftop measures ending at 9am on the day of the subject's visit (-2.0% [-20.3%; 16.4%]). Conclusion: The stronger correlation of the midnight-to-midnight measures with those rooftop measures starting at 9am suggests that both exposure windows may be influenced by similar factors, perhaps factors present early in the day. The stronger FMD association with the PM measures beginning at 9am is surprising and suggests that these early-day factors may be important in understanding endothelial dysfunction. Weare using hourly network data to further analyze the influence of the 9-, 6-and 4-hour PM averages preceding the FMD assessment. This abstract of a proposed presentation does not necessarily represent EPA policy.