Particulate matter and heart rate variability among elderly retirees: the Baltimore 1998 PM study

This study investigates the relationship between ambient fine particle poll ution and impaired cardiac autonomic control in the elderly. Heart rate var iability (HRV) among 56 elderly (mean age 82) nonsmoking residents of a ret irement center in Baltimore County, Maryland, was monitored for 4 weeks, fr om July 27 through August 22, 1998. The weather was seasonally mild (63 - 8 4 degreesF mean daily temperature) with low to moderate levels of fine part icles ( PM2.5 < 50 mug/m(3)). Two groups of approximately 30 subjects were examined on alternate days. A spline mixed - effects model revealed a negat ive relationship between outdoor 24 - h average fine particulate matter (PM 2.5) and high- frequency (HF) HRV that was consistent with our earlier Balt imore study for all but 2 days. These 2 days were the only days with signif icant precipitation in combination with elevated PM2.5 They were also unusu al in that back - trajectory of their air masses was distinctly different f rom those on the other study days, emanating from the direction of rural Pe nnsylvania. Mixed - effects analysis for all 24 study days showed a small n egative association of outdoor PM2.5 with HF HRV ( - 0.03 change in log[HF HRV] for a 10 mug/m(3) increment in PM2.5) after adjustment for age, sex, c ardiovascular status, trend, maximum temperature, average dew point tempera ture, random subject intercepts, and autocorrelated residuals. After exclud ing study days 4 and 5. this association was strengthened ( - 0.07 change i n log[HF HRV] for 10 mug/m(3) PM2.5, 95% CI -0.13 to - 0.02) and was simila r to that obtained in an earlier study ( - 0. 12 change in log[HF HRV ] for a 10 mug/m(3) increment in outdoor PM2.5, 95% CI - 0.24 to - 0.00) [Liao D ., Cai J.. Rosamond W.D., Barnes R.W., Hutchinson R.G., Whitsel E.A., Rauta harju P., and Heiss G. Cardiac autonomic function and incident coronary hea rt disease: a population - based case - cohort study. The ARIC Study. Ather osclerosis Risk in Communities Study. Am J Epidemiol 1997: 145 (8): 696-706 ]. Acute ( 1 to 4 h) previous PM2.5 exposure did not have a stronger impact than the 24-h measure. A distributed lag model incorporating the six prece ding 4-h means also did not indicate any effect greater than that observed in the 24-h measure. This study is consistent with earlier findings that ex posures to PM2.5 are associated with decreased HRV in the elderly.