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. 2005 Nov 15;114(4):560–566. doi: 10.1289/ehp.8337

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Percent change in SDNN with 4-hr PM_2.5 (A) and NO₂ (B), expressed with 95% CI per IQR change in PM_2.5 (10.64 μ g/m³) or NO₂ (10.75 ppb). Medication use status is based on whether participant took medication on the morning of the health measurement. All percent changes differed significantly by medication use at p = 0.05.