Traffic-related air pollution is associated with increased blood pressure

1. In this randomized crossover trial, mean systolic and diastolic blood pressures were higher for unfiltered drives at one hour and 24 hours after drive initiation, respectively. 

2. Adjusted mean central retinal arteriolar equivalents (CRAE) were unchanged between filtered and unfiltered days.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Traffic-related air pollution (TRAP) is an air pollution mixture produced by vehicle exhaust as well as break and tire wear. It consists of ultrafine particles including black carbon, nitrogen oxides, carbon monoxide, carbon dioxide, and particulate matter less than 2.5 µm in diameter (PM2.5). Increased exposure to air pollution has been associated with cardiovascular disease, which is thought to be mediated through inflammatory pathways and autonomic dysregulation. Previous studies have suggested atherosclerotic changes in response to controlled pollution exposure, including blood pressure changes up to 24 hours following exposure. This trial aimed to investigate the effects of TRAP on blood pressure and vascular changes using in-vehicle scripted commutes through rush-hour traffic in Seattle, Washington. The study demonstrated elevations in adjusted mean systolic and diastolic blood pressures for unfiltered drives at one hour and 24 hours after drive initiation, respectively. Adjusted mean CRAE values were unchanged between filtered and unfiltered drives. The results of this study were limited by a small sample size and the inability to control for seasonal changes in its drive sequences, impacting the efficacy of the filtration devices.

Click to read the study in AIM

In-Depth [randomized controlled trial]: This double-blinded, randomized crossover trial utilized in-vehicle scripted commutes and particle filtration to investigate the effects of TRAP on blood pressure and retinal vasculature. In total, 16 normotensive persons aged 22 to 45 were included in the study, although blood pressure endpoints were ultimately unavailable in three participants. Participants were randomly assigned to the order of exposure, which included two separate drives without filtration and one drive with filtration, for a total of three two-hour drives through rush-hour Seattle traffic. In the study, the participants exhibited a mean age of 29.7 years with pre-drive systolic and diastolic blood pressures of 122.7 mmHg and 70.8 mmHg, respectively. Filtration reduced particle count by 86% but was generally ineffective for gaseous particles. At one hour after drive initiation, the adjusted mean systolic pressure was 4.5 mmHg higher (95% Confidence Interval [CI], -1.2 to 10.2 mmHg) for unfiltered drives versus filtered drives and the mean diastolic pressure was 4.7 mmHg higher (95% CI, 0.9 to 8.4 mmHg). At 24 hours following drive initiation, the systolic pressure was 1.1 mmHg higher (CI, -4.6 to 6.8 mmHg) and the diastolic pressure was 3.8 mmHg higher (CI, 0.02 to 7.5 mmHg) for unfiltered drives. These temporal changes in blood pressure were consistent with findings in previous studies. Moreover, the CRAE was 2.7 µm wider for unfiltered drives (CI, -1.5 to 6.8 µm). In summary, this study demonstrated net increases in blood pressure one hour and 24 hours after drive initiation in the context of TRAP exposure.

Image: PD

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