Does chronic exposure to high levels of nitrogen dioxide exacerbate the short-term effects of airborne particles?
研究长期二氧化氮暴露是否改变颗粒物短期暴露对死亡率的影响，发现整体人群无显著修饰作用，但在85岁以上老人及有心律失常或慢阻肺病史者中效应增强。
<h3>Background</h3> Long-term exposure to air pollutants has been hypothesised as a factor in susceptibility to short-term exposure to particulate matter (PM), but results are not coherent. We studied the short-term effects of PM<sub>10</sub> on mortality and assessed whether long-term exposure to nitrogen dioxide (NO<sub>2</sub>) modifies this association. <h3>Methods</h3> We used a case-crossover design to evaluate daily PM<sub>10</sub>-related mortality among 124 432 35+ year-old participants who died in Rome between 2001 and 2010 and maintained the same address for at least 5 years before death. Modification of PM<sub>10</sub>-related mortality by long-term NO<sub>2</sub> exposure was determined by two-way interaction, while a three-way interaction was used to assess effect modification of high NO<sub>2</sub> levels in population groups defined by sociodemographic position and pre-existing diseases. <h3>Results</h3> Mortality increased by 0.82% (0.23–1.41%) for each 10 µg/m<sup>3</sup> increase in PM<sub>10</sub>. Mortality rose by 1.22% (0.17–2.38%) in participants exposed to NO<sub>2</sub> levels ≥50 µg/m<sup>3</sup> and by 0.69% (0.03–1.34%) in those exposed to levels <50 µg/m<sup>3</sup> with no effect modification (p-interaction 0.378). A suggestion of effect modification was seen in 85+-year-olds (3.10%; p-interaction 0.043), as well as in those with a pre-existing arrhythmia (3.26%; p-interaction 0.014) and chronic obstructive pulmonary disease (3.52%; p-interaction 0.042). <h3>Conclusions</h3> Long-term exposure to NO<sub>2</sub> is not likely to induce susceptibility to short-term PM<sub>10</sub> exposure in the overall population. However, an effect modification of NO<sub>2</sub> is probable in the elderly and in those suffering from arrhythmias and chronic obstructive pulmonary disease.