Impact of traffic-related air pollution on the blood pressure response to exercise in individuals with hypertension

Abstract

Funding Acknowledgements Type of funding sources: Foundation. Main funding source(s): Natural Sciences and Engineering Research Council of Canada and B.C. Sports & Exercise Medicine Research Foundation. Background The epidemiologic evidence suggests that the health benefits of exercise in healthy adults outweigh the adverse effects of air pollution in all but the most extreme concentrations. However, no studies have examined the acute response to exercise in air pollution in individuals with hypertension, a subgroup particularly susceptible to the cardiovascular effects of air population. Purpose The purpose of this study was to determine the impact of traffic-related air pollution on the acute cardiovascular response to exercise in patients with hypertension. We hypothesized that exposure to higher levels of traffic-related air pollution during exercise would attenuate, but not eliminate, acute post-exercise reductions in blood pressure and arterial stiffness. Methods Fourteen patients with hypertension (62.4±6.8 years; 81% male) completed a real-world, randomized, crossover study. Two 30-minute exercise bouts at 40-59% heart rate reserve were performed: once along a commercial street (high traffic) and once in an urban plaza (low traffic). Blood pressure (BP) and arterial stiffness (i.e., carotid-femoral pulse wave velocity [cfPWV]) were examined prior to, 30 minutes after, and 2 hours following exercise. 24-hour ambulatory BP monitoring was immediately completed following each visit. Black carbon, noise, relative humidity, and temperature were measured during each exercise bout (Figure 1). Results No differences were found for baseline cardiovascular measures between high and low traffic visits. At 30 minutes and 2 hours post-exercise, systolic BP was significantly reduced relative to baseline in the low-traffic condition only; diastolic BP was not significantly reduced at any timepoint. Based on linear mixed-effects analyses, exercising at the low traffic site was associated, relative to the high traffic site, with a significant (p = 0.04) reduction in systolic BP (-4.30 mm Hg [95% CI -8.09 to -0.54]) up to 2 hours following exercise after adjusting for exercise intensity, temperature, and noise; no differences were found for diastolic BP (-1.56 mm Hg [95% CI -4.87 to 1.83], p = 0.39). Each interquartile increase in black carbon (1168 ng/m³) was significantly associated with a 2.33 mm Hg (95% CI 0.37 to 4.17) increase in systolic BP up to 2 hours following exercise. No associations were observed between traffic site and BP for any ambulatory periods (i.e., 24-hour average, daytime, nighttime, or evening). The acute cfPWV response to exercise was also similar between traffic sites (p > 0.05). Conclusion Our findings suggest that exposure to traffic-related air pollution during exercise may adversely impact the beneficial short-term BP response to exercise in patients with hypertension. While the long-term implications of these changes to the acute BP response to exercise must be further explored, patients with hypertension can employ the prudent strategy of maximizing their distance from major roadways when exercising.