Diesel Exhaust Particles Affected Heart Rate Variability but Not Endothelial Function – Results from a Controlled Chamber Study

Background Adverse cardiovascular effects have been associated with exposure to both diesel exhaust and road traffic noise. Effects of these highly correlated exposures are hard to disentangle in epidemiological studies, but effects on intermediary outcomes and mechanisms can be studied experimentally. Heart rate variability (HRV) and peripheral arterial tonometry (PAT), a measure of endothelial function, are noninvasive methods to study mechanisms related to the autonomic nervous system associated with cardiovascular risk. The aim of this study was to evaluate the impact of diesel exhaust particles and traffic noise on HRV and PAT, and possible synergistic effect of combined exposure. Methods Eighteen healthy adults were in a controlled chamber exposed to four exposure scenarios in a randomized cross-over fashion. Each scenario consisted of either filtered (clean) air or diesel engine exhaust (PM concentrations around 300 µg/m3), and low (46 dB(A)) or high (75 dB(A)) traffic noise for three hours at rest. ECG was recorded for 10-minute periods before and during each scenario, and frequency-domain heart rate variability (HRV) computed. Endothelial function and arterial stiffness were assessed after each exposure using EndoPAT 2000. Results Compared to the control scenario, HRV in the high frequency band decreased during exposure to diesel exhaust, both alone and combined with noise, but not during exposure to noise only. The differences were stronger in women. There were no synergistic effects of combined exposure, no significant differences between exposure scenarios for other HRV indices, and no effect on endothelial function or arterial stiffness after exposure. Conclusion Three-hour exposure to diesel exhaust, but not noise, was associated with decreased HRV in the high frequency band. This indicates activation of irritant receptor-mediated autonomic reflexes, and increased cardiovascular risk during chronic diesel exposure. Keywords Diesel, PM1, noise, heart rate variability, endothelial function, cardiovascular