Pulmonary Function And Heart Rate Variability Responses To Low- And High-intensity Cycling In Diesel Exhaust

Abstract

INTRODUCTION: Exposure to diesel exhaust (DE) prior to exercise increases exercise heart rate and attenuates exercise-induced bronchodilation. However, the effects of exercise combined with air pollution on pulmonary function and heart rate variability (HRV) are unclear. Furthermore, it is often assumed that increases in exercise intensity will increase the dose of air pollution, thus magnifying the resultant health effects. However, how the effects of DE on pulmonary function and HRV are modulated by exercise intensity is unknown. PURPOSE: To determine the effects to low- and high-intensity cycling in DE on pulmonary function and HRV. METHODS: Eighteen males performed 30-minute trials of low (30% VO2peak power) and high-intensity (60% VO2peak power) cycling and a resting control condition. For each subject, each trial was performed once breathing filtered air (FA) and once breathing DE (300ug/m3 of PM2.5), for a total of 6 trials. Pulmonary function and HRV were measured before, immediately after, and 1 h, and 2 h post-exposure to DE or FA. Time domain measures of HRV included the standard deviation of normal-to-normal intervals (SDNN), the root mean square of the mean differences in successive N-N intervals (RMSSD), and the HRV triangular index. Frequency domain analysis included low frequency power (LFP: 0.04–0.15 Hz), high frequency power (HFP: 0.15–0.40 Hz) as well as total power (TP). Additionally, LF and HF normalized units (LFnu, HFnu), and LF/HF ratios were determined. RESULTS: Exposure to DE had no significant effect on pulmonary function or HRV (p<0.05). As expected all time and frequency domain indices of HRV significantly decreased following high-intensity exercise (p<0.05; Pre to post high-intensity exercise: SDNN 1018.7 vs. 730.1 ms, RMSSD 65.2 vs. 19.5 ms, HRV triangular index 14.3 vs. 7.2, LFP 1408.8 vs. 455.7 ms2, HFP 1487.0 vs. 391.1 ms2, TP 4949.0 vs. 1152.8 ms2, HFnu 44.5 vs. 19.8). The exception to this pattern was LFnu and LF/HF ratio, which significantly increased following high-intensity exercise (p<0.05; Pre to post high-intensity exercise: LFnu 51.7 vs. 71.8, LF/HF 1.49 vs. 4.52). CONCLUSION: These data suggest that acute exposure to DE during exercise does not affect pulmonary function or HRV. Furthermore, performing high intensity exercise does not potentiate the effects of DE.