Traffic-Related Air Pollution and Acute Changes in Heart Rate Variability and Respiratory Function in Urban Cyclists

Abstract

Background: Few studies have examined the acute health effects of air pollution exposures experienced while cycling in traffic.

Objectives: We conducted a crossover study to examine the relationship between traffic pollution and acute changes in heart rate variability. We also collected spirometry and exhaled nitric oxide measures.

Methods: Forty-two healthy adults cycled for 1 hr on high- and low-traffic routes as well as indoors. Health measures were collected before cycling and 1–4 hr after the start of cycling. Ultrafine particles (UFPs; ≤ 0.1 μm in aerodynamic diameter), particulate matter ≤ 2.5 μm in aerodynamic diameter (PM _2.5), black carbon, and volatile organic compounds were measured along each cycling route, and ambient nitrogen dioxide (NO ₂) and ozone (O ₃) levels were recorded from a fixed-site monitor. Mixed-effects models were used to estimate associations between air pollutants and changes in health outcome measures relative to precycling baseline values.

Results: An interquartile range increase in UFP levels (18,200/cm ³) was associated with a significant decrease in high-frequency power 4 hr after the start of cycling [β = –224 msec ²; 95% confidence interval (CI), –386 to –63 msec ²]. Ambient NO ₂ levels were inversely associated with the standard deviation of normal-to-normal (NN) intervals (β = –10 msec; 95% CI, –20 to –0.34 msec) and positively associated with the ratio of low-frequency to high-frequency power (β = 1.4; 95% CI, 0.35 to 2.5) 2 hr after the start of cycling. We also observed significant inverse associations between ambient O ₃ levels and the root mean square of successive differences in adjacent NN intervals 3 hr after the start of cycling.

Conclusions: Short-term exposures to traffic pollution may contribute to altered autonomic modulation of the heart in the hours immediately after cycling.