Kristina Shkirkova, BSc
The risk factors of stroke, a major contributor to the global burden of disability and mortality, include environmental exposure to air pollution. Pre-stroke long-term exposure to air pollution derived particulate matter is associated with higher mortality rates after ischemic stroke, the authors of the new study from China report.
The study by Chen et al. estimated the daily exposure of a cohort of 12291 ischemic stroke patients to air pollutants via a machine learning algorithm that accounted for temporal and spatial meteorological and satellite monitoring data for the geocoded location of patients’ home address. The authors looked at 3-year pre-stroke air levels of particulate matter with aerodynamic diameter ≤10 μm and nitrogen dioxide and the rates of mortality after ischemic stroke within 1 year follow up period between 2007 and 2008. Smaller coarse particles in the air mixture were the primary interest in this study, as they contain the most toxin and are able penetrate deeper through the respiratory system and cause an inflammatory response.
Among 12 291 ischemic stroke patients included in the study, 1649 (13.4%) deaths occurred within 1 year. Among 1649 deaths, 62% were from large-artery atherosclerosis, 23% from cardioembolism, and 10% from small-artery occlusion. After controlling for confounders, such as age, stroke severity, smoking and stroke risk factors, significant associations were observed between ultra-fine particulate matter, PM1 1.05 (1.02-1.09) and PM2.5 1.03 (1.00-1.06), and deaths from stroke. Mean exposure levels to PM1 and PM2.5 for patients who died after stroke were 63.3 μg/m3 and 80.6 μg/m3, respectively. Mean exposure levels for those who survived were 62.1 μg/m3 and 79.6 μg/m3, respectively. Exposure to PM10 and NO2 was not significantly associated with risk of death. Additional stratified analysis indicated that PM1 exposure was more strongly associated with death among males 1.06 (1.02-1.11) than females 1.04 (0.99-1.08), patients over 75 years old 1.06 (1.01-1.11) than patients between 65 and 75 years old 1.04 (0.99-1.10), and obese patients 1.07 (1.02-1.12) compared to normal weight patients 1.01 (0.96-1.05).
The authors propose that particulate matter may cause impairment of vascular function leading to increase in blood pressure, blood coagulability, and inflammatory states as potential mechanisms that may explain a strong association between stroke mortality and living in more heavily polluted areas. The data from this study, combined with global rising levels of air pollution, highlights the importance of policies to establish safe standards of air pollution exposure. Reducing air pollution exposure may contribute to the recovery of patients with stroke.