Abstract
BACKGROUND: Human controlled-exposure studies have assessed the impact of ambient fine particulate matter on cardiac autonomic function measured by heart rate variability (HRV), but whether these effects are modified by concomitant ozone exposure remains unknown. OBJECTIVE: In this study we assessed the impact of O(3) and particulate matter exposure on HRV in humans. METHODS: In a crossover design, 50 subjects (19-48 years of age) were randomized to 2-hr controlled exposures to filtered air (FA), concentrated ambient particles (CAPs), O(3), or combined CAPs and ozone (CAPs + O(3)). The primary end point was change in HRV between the start and end of exposure. Secondary analyses included blood pressure (BP) responses, and effect modification by asthmatic status. RESULTS: Achieved mean CAPs and O(3) exposure concentrations were 121.6 +/- 48.0 microg/m(3) and 113.9 +/- 6.6 ppb, respectively. In a categorical analysis, exposure had no consistent effect on HRV indices. However, the dose-response relationship between CAPs mass concentration and HRV indices seemed to vary depending on the presence of O(3). This heterogeneity was statistically significant for the low-frequency component of HRV (p = 0.02) and approached significance for the high-frequency component and time-domain measures of HRV. Exposure to CAPs + O(3) increased diastolic BP by 2.0 mmHg (SE, 1.2; p = 0.02). No other statistically significant changes in BP were observed. Asthmatic status did not modify these effects. CONCLUSION: The potentiation by O(3) of CAPs effects on diastolic BP and possibly HRV is of small magnitude in young adults. Further studies are needed to assess potential effects in more vulnerable populations.