Effect of Traffic-Related Air Pollution on Spontaneous Baroreceptor Sensitivity: A Trial of In-Vehicle Filtration

Abstract

Human controlled exposure studies suggest that diesel exhaust causes acute changes in blood pressure that are mediated by sympathetic activation, but it is unknown whether this sympathetic response might also cause imbalance directly affecting cardiac autonomic control. Baroreceptor sensitivity (BRS) measures rapid compensatory regulation of heart rate in response to acute changes in blood pressure. Using a crossover trial of real-world in-vehicle commutes, we tested whether exposure to traffic-related air pollutants (TRAP) affects spontaneous BRS in healthy subjects.Young healthy participants were driven through heavy Seattle, WA traffic for two hours on three different days, each separated by several weeks. On two days, on-road air was entrained into the cabin through the vehicle’s factory air vents and sham filters. On another day, the vehicle was equipped with effective filtration. Exposure was double-blinded and participants were randomized to order of exposure. Three minute intervals of continuous blood pressure and pulse intervals were recorded before, during, and up to 24 hours after drive using a Finapres finger pulse waveform device. BRS was calculated as the reduced major axis slope for change in pulse interval per change in blood pressure for rolling 10 second intervals.On filtered days in-vehicle average particle count was reduced by 85%. We used a mixed effects model on the outcome of change from pre-drive BRS measurements, comparing filtered versus unfiltered day at all thirteen time points in nine subjects with measurable BRS, after excluding a single subject with very large changes in BRS. A likelihood ratio test for the effect of filtration on BRS at all time points was not significant (p=0.95). At 7 hours after drive start, BRS, relative to pre-drive levels, was on average 1.01 ms/mmHg higher (95% CI:-7.4, 9.4) in unfiltered drives compared to filtered drives. In conclusion, we did not find evidence that TRAP inhalation causes acute change in BRS.