Cardiorespiratory responses to fine particles during ambient PM2.5 pollution waves: Findings from a randomized crossover trial in young healthy adults

Background: PM2.5 pollution waves (PPWs) are severe air pollution events with extremely high-level concentration of ambient PM2.5. PPWs, such as haze days, were suggested to be associated with increased cardiopulmonary mortality and morbidity. However, the biological mechanism response to ambient PM2.5 during PPWs is still unclear. Methods: A randomized crossover trial was conducted on 29 healthy young adults. Repeated health measurements were performed before, during and after two typical PPWs under filtered and sham indoor air purification, with a washout interval of at least 2 weeks. Health parameters including blood pressure (BP), pulmonary function, fractional exhaled nitric oxide (FeNO) and circulating biomarkers which reflect platelet activation, blood coagulation and systematic oxidative stress were measured. Results: Ambient PM2.5 levels elevated apparently during PPWs. Under sham purification, significant increase in FeNO and soluble P-selectin (sP-selectin) and decreases in pulmonary function were observed from pre-PPWs period to during-PPWs period. The changes in health biomarkers as mentioned above became attenuated and insignificant under filtered condition. For instance, sP-selectin increased by 12.0% (95% CI: 3.8%, 20.8%) during-PPWs periods compared with pre-PPWs periods under sham purification, while non-significant change was observed under filtered condition. Significant associations between time-weighted personal PM2.5 exposure and increased levels of health biomarkers including FeNO, sP-selectin, oxidized low-density lipoprotein (ox-LDL) and 8-isoprostane (8-isoPGF2α) were found. Conclusion: PPWs could affect cardiopulmonary health through systematic oxidative stress, platelet activation and respiratory inflammation in healthy adults, and short-term indoor air purification could alleviate the adverse cardiopulmonary effects.