Effects of diesel exhaust inhalation on heart rate variability in human volunteers

Objectives: Particulate matter (PM) air pollution is associated with alterations in cardiac conductance and sudden cardiac death in epidemiological studies. Traffic-related air pollutants, including diesel exhaust (DE) may be at least partly responsible for these effects. In this experimental study we assessed whether short-term exposure to DE would result in alterations in heart rate variability (HRV), a non-invasive measure of autonomic control of the heart. Methods: In a double-blind, crossover, controlled-exposure study, 16 adult volunteers were exposed (at rest) in randomized order to filtered air (FA) and two levels of diluted DE (100 or 200 μg/m³ of fine particulate matter) in 2-h sessions. Before, and at four time points after each exposure we assessed HRV. HRV parameters assessed included both time domain statistics (standard deviation of N-N intervals (SDNN), and the square root of the mean of the sum of squared differences between successive N-N intervals (RMSSD)) and frequency domain statistics (high-frequency (HF) power, low-frequency (LF) power, and the LF/HF ratio). Results: We observed an effect at 3-h after initiation of DE inhalation on the frequency domain statistics of HRV. DE at 200 μg/m³ elicited an increase in HF power compared to FA (Δ=0.33; 95% CI: 0.01-0.7) and a decrease in LF/HF ratio (Δ=-0.74; 95% CI: -1.2 to -0.2). The effect of DE on HF power was not consistent among study participants. There was no DE effect on time domain statistics and no significant DE effect on HRV in later time points. Conclusions: We did not observe a consistent DE effect on the autonomic control of the heart in a controlled-exposure experiment in young participants. Efforts are warranted to understand discrepancies between epidemiological and experimental studies of air pollution's impact on HRV.