Differential effects of fine and coarse particulate matter on hospitalizations for ischemic heart disease: A population-based time-series analysis in Southwestern China

Few studies have explored the associations of ischemic heart disease (IHD) hospitalizations with fine (diameter ≤ 2.5 μm, PM_2.5) and coarse particulate matter (diameter between 2.5 and 10 μm, PM_C) simultaneously; and studies to distinguish the susceptible populations by sex, age, and comorbidity status are sparse and inconsistent. This study aimed to assess the differential effects of PM_2.5 and PM_C on IHD hospitalizations and to investigate modifiers of demographic characters, causes of hospitalizations, and comorbidity status on these differential effects. A time-series analysis using an over-dispersed generalized additive model on 33017 IHD hospitalizations was conducted in urban areas of Chengdu, Southwestern China, from 1 January 2015 to 31 December 2016. Z-test was used to test whether PM_C- or PM_2.5-related effects were differential within each modifier. Furthermore, to evaluate the robustness of the key findings for gaseous pollutants exposure adjustment, co-pollutant models were constructed. We identified differential effects of PM_2.5 and PM_C on IHD hospitalizations in terms of the effect magnitude, effect stability, and susceptible populations. A 10 μg/m³ increment of PM_2.5 and PM_C at lag06 was associated with a 1.2% (95% confidence interval (CI): 0.3%, 2.2%) and 2.5% (95%CI: 1.1%, 3.8%) increase in IHD hospitalizations, respectively. After adjustment for gaseous pollutants, PM_C effect was independent, particularly among males, angina, chronic IHD, and patients with comorbidity of chronic heart failure, hypertension, or chronic obstructive pulmonary disease (COPD); whereas, PM_2.5 effect remained significant among patients with comorbidity of hypertension. Males, comorbidity of hypertension or COPD substantially increased the PM_C-related risk for IHD hospitalizations; whereas, only comorbidity of hypertension increased the PM_2.5-related risk for IHD hospitalizations. Interestingly, the PM_C effect was comparable between the middle-aged and the elderly. Our study found differential effects of PM_2.5 and PM_C on IHD hospitalizations and identified susceptible populations, which are important to establish guidelines or recommendations for high-risk individuals.