Figure 3.

The effect of particulate matter with aerodynamic diameter <2.5 μm (PM_2.5) exposure on heart rate variability (HRV) at different mean Toll‐like receptor 2 (TLR2) methylation levels, Normative Aging Study, 2000–2011 (N=500). log₁₀HR indicates log₁₀‐transformed heart rate; log₁₀rMSSD, log₁₀‐transformed root mean square of the successive differences; log₁₀SDNN, log₁₀‐transformed standard deviation of normal‐to‐normal intervals; log₁₀LF, log₁₀‐transformed low‐frequency power (0.04 to 0.15 Hz); log₁₀HF, log₁₀‐transformed high‐frequency power (0.15 to 0.4 Hz); Q1, Q2, Q3, and Q4 indicate the first, second, third, and fourth quartiles. The association of PM_2.5 with rMSSD, SDNN, LF, and HF is modified by mean TLR2 methylation levels, as indicated by the different slopes. The 4 lines in each figure represent the relationship between PM_2.5 and HRV when the mean TLR2 methylation level is at the midpoints of each quartile. If there was no effect modification, the 4 lines would be the same. The P_global for interaction was based on a global test for effect modification by position‐specific methylation. Interaction terms between each of the 5 TLR2 positions and PM_2.5 were included in the model, and these 5 interaction terms were tested jointly for effect modification using a Wald test (global test). Results were adjusted for age; body mass index; fasting glucose level; hypertension; smoking status; alcohol consumption; physical exercise; household income; the use of calcium channel blocker, β‐blocker, and angiotensin‐converting enzyme inhibitor; room temperature; outdoor apparent temperature; season; weekday; and visit date.