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Diane R. Gold,^1,2 Augusto A. Litonjua,¹ Antonella Zanobetti,² Brent A. Coull,³ Joel Schwartz,² Gail MacCallum,⁴ Richard L. Verrier,⁵ Bruce D. Nearing,⁵ Marina J. Canner,¹ Helen Suh,⁶ and Peter H. Stone⁴

¹Channing Laboratory, Brigham and Women's Hospital, Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA; ²Environmental Epidemiology Program, Department of Environmental Health, and ³Environmental Statistics Program, Department of Biostatistics, Harvard School of Public Health, Boston, Massachusetts, USA; ⁴Cardiology Division, Brigham and Women's Hospital, Department of Medicine, Boston, Massachusetts, USA; ⁵Division of Cardiology, Beth Israel Deaconess Medical Center, Department of Medicine, Harvard Medical School, Boston, Massachusetts, USA; ⁶Environmental Science and Engineering Program, Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, USA

Abstract
Increased levels of daily ambient particle pollution have been associated with increased risk of cardiovascular morbidity. Black carbon (BC) is a measure of the traffic-related component of particles. We investigated associations between ambient pollution and ST-segment levels in a repeated-measures study including 269 observations on 24 active Boston residents 61-88 years of age, each observed up to 12 times from June through September 1999. The protocol involved continuous Holter electrocardiogram monitoring including 5 min of rest, 5 min of standing, 5 min of exercise outdoors, 5 min of recovery, and 20 cycles of paced breathing. Pollution-associated ST-depression was estimated for a 10th- to 90th-percentile change in BC. We calculated the average ST-segment level, referenced to the P-R isoelectric values, for each portion of the protocol. The mean BC level in the previous 12 hr, and the BC level 5 hr before testing, predicted ST-segment depression in most portions of the protocol, but the effect was strongest in the postexercise periods. During postexercise rest, an elevated BC level was associated with -0.1 mm ST-segment depression (p = 0.02 for 12-hr mean BC ; p = 0.001 for 5-hr BC) in continuous models. Elevated BC also predicted increased risk of ST-segment depression ≥ 0.5 mm among those with at least one episode of that level of ST-segment depression. Carbon monoxide was not a confounder of this association. ST-segment depression, possibly representing myocardial ischemia or inflammation, is associated with increased exposure to particles whose predominant source is traffic. Key words: air pollution, cardiology, elderly, particles, ST-segment depression, traffic. Environ Health Perspect 113: 883-887 (2005) . doi:10.1289/ehp.7737 available via http://dx.doi.org/ [Online 14 March 2005]

Address correspondence to D.R. Gold, Channing Laboratory, Brigham and Women's Hospital, Harvard Medical School, 181 Longwood Ave., Boston, MA 02215 USA. Telephone: (617) 525-2738. Fax: (617) 525-0950. E-mail: diane.gold@channing.harvard.edu

This work was supported in part by National Institutes of Health grant 5 P01 ES09825, U.S. Environmental Protection Agency (EPA) Cooperative Agreement CR821762, EPA 826780-01-0, and EPA R827353-01-0.

The authors declare they have no competing financial interests.

Received 8 November 2004 ; accepted 14 March 2005.