Particulate pollution and stroke

(Particle pollution, or particulate matter (PM), is a mix of tiny solid/liquid droplets in the air, categorized by size (PM10, PM2.5), originating from sources like vehicle exhaust, industry, and fires, and causing serious heart/lung issues (asthma, heart attacks) by penetrating deep into the body. Key concerns are fine particles (PM2.5) and ultrafine particles that can reach the bloodstream, impacting overall health and visibility)

Exposure to PM10 showed weaker associations with admission to hospital for stroke or mortality from stroke than PM2.5, consistent with observations from other meta-analyses for stroke42 

and acute myocardial infarction.3 This could reflect differences in particle size, with larger particles more likely to exert local pulmonary effects whereas fine or ultrafine particles (PM2.5) or gaseous pollutants could cause additional systemic cardiovascular effects.36

 In contrast, the adverse effect of larger particles in patients with heart failure was more striking, possibly reflecting indirect biological pathways such as the adverse effect of sympathetic nervous activation on the failing heart.4 36 We noticed greater heterogeneity for PM2.5 than for PM10.

 These differences in heterogeneity persisted after subgroup analysis and could reflect variation in study design. 

We were able to meta-analyse twice as many estimates for PM10 than for PM2.5, with an overall less marked but more consistent effect of exposure on stroke with PM10.

 There are several biologically plausible reasons for this. While there is a close correlation between PM2.5 and PM10 concentrations, 

epidemiological studies have shown that the association between PM10 and acute cardiovascular events is primarily driven by the PM2.5 fraction.47

 This fraction is enriched with ultrafine particles derived from the combustion of fossil fuels

, which toxicology studies have suggested are the most potent component of particulate matter.48

 These particles are potentially small enough to translocate from the lungs into the circulation and are therefore perhaps more likely to trigger acute cardiovascular episodes

.49 Interestingly, all three gaseous pollutants derived from combustion (nitrogen dioxide, sulphur dioxide, and carbon monoxide) were associated with stroke, and this was consistent with reported associations with admission for heart failure and acute myocardial infarction.3 4 3

Ref

 BMJ. 2015 Mar 24;350:h1295. doi: 10.1136/bmj.h1295

Short term exposure to air pollution and stroke: systematic review and meta-analysis

Anoop S V Shah 1,✉, Kuan Ken Lee 1, David A McAllister 2, Amanda Hunter 1, Harish Nair 2, William Whiteley 3, Jeremy P Langrish 1, David E Newby 1, Nicholas L Mills