Impact of ozone exposure on heart rate variability and stress hormones: A randomized-crossover study.

The biological mechanisms underlying the associations between atmospheric ozone exposure and adverse cardiometabolic outcomes are yet to be identified. Imbalanced autonomic nervous system (ANS) as well as activations of the sympatho-adrenomedullary (SAM) and hypothalamic-pituitary-adrenal (HPA) axes are among possible early biological responses triggered by ozone, and may eventually lead to cardiometabolic abnormalities. To determine whether acute ozone exposure causes ANS imbalance and increases the secretion of neuroendocrine stress hormones, we conducted a randomized, double-blind, crossover trial, under controlled 2-hour exposure to either ozone (200 ppb) or clean air with intermittent exercise among 22 healthy young adults. Here we found that, compared to clean air exposure, acute ozone exposure significantly decreased the high-frequency band of heart rate variability, even after adjusting for heart rate and pre-exposure to ambient air pollutants and meteorological factors. Ozone exposure also significantly increased the serum levels of stress hormones, including corticotrophin-releasing factor, adrenocorticotropic hormone, adrenaline, and noradrenaline. Metabolomics analysis showed that acute ozone exposure led to alterations in stress hormones, systemic inflammation, oxidative stress, and energy metabolism. Our results suggest that acute ozone exposure may trigger ANS imbalance and activate the HPA and SAM axes, offering potential biological explanations for the adverse cardiometabolic effects following acute ozone exposure.

Particulate matter air pollution and reduced heart rate variability: How the associations vary by particle size in Shanghai, China.

BACKGROUND: It remains unclear which size of particles has the strongest effects on heart rate variability (HRV). OBJECTIVE: To explore the association between HRV parameters and daily variations of size-fractionated particle number concentrations (PNCs). METHODS: We conducted a longitudinal repeated-measure study among 78 participants with a 24-h continuous ambulatory Holter electrocardiographic recorder in Shanghai, China, from January 2015 to June 2019. Linear mixed-effects models were employed to evaluate the changes of HRV parameters associated with PNCs of 7 size ranges from 0.01 to 10 µm after controlling for environmental and individual confounders. RESULTS: On the concurrent day, decreased HRV parameters were associated with increased PNCs of 0.01-0.3 µm, and smaller particles showed greater effects. For an interquartile range increase in ultrafine particles (UFP, those < 0.1 µm, 2453 particles/cm3), the declines in very-low-frequency power, low-frequency power, high-frequency power, standard deviation of normal R-R intervals, root mean square of the successive differences between R-R intervals and percentage of adjacent normal R-R intervals with a difference ≥ 50 ms were 5.06% [95% confidence interval (CI): 2.09%, 7.94%], 7.65% (95%CI: 2.73%, 12.32%), 9.49% (95%CI: 4.64%, 14.09%), 5.10% (95%CI: 2.21%, 7.91%), 8.09% (95%CI: 4.39%, 11.65%) and 24.98% (95%CI: 14.70%, 34.02%), respectively. These results were robust to the adjustment of criteria air pollutants, temperature at different lags, and the status of heart medication. CONCLUSIONS: Particles less than 0.3 µm (especially UFP) may dominate the acute effects of particulate air pollution on cardiac autonomic dysfunction.

Fine particulate matter constituents and heart rate variability: A panel study in Shanghai, China.

BACKGROUND: Short-term exposure to fine particulate matter (PM2.5) has been associated with reduced heart rate variability (HRV), an established indicator of cardiac autonomic function, but it remains uncertain which specific constituents of PM2.5 had key impacts. OBJECTIVE: To examine the short-term associations between various PM2.5 constituents and HRV measures. METHODS: We conducted a retrospective panel study among 78 participants who received repeated 24-h electrocardiogram testing in Shanghai, China from 2015 to 2019. We obtained daily concentrations of 14 main chemical constituents of PM2.5 from a fixed-site monitor. During 3 or 4 rounds of follow-ups, we measured 6 HRV parameters, including 3 frequency-domain parameters (power in very low frequency, low frequency and high frequency) and 3 time-domain parameters (standard deviation of normal-to-normal intervals, root mean square successive difference and percent of adjacent normal R-R intervals with a difference ≥50 msec). We used linear mixed-effects models to analyze the data after controlling for time trends, environmental and individual risk factors. RESULTS: The average daily PM2.5 exposure was 45.8 µg/m3 during the study period. The present-day exposure to PM2.5 had the strongest negative influences on various HRV indicators. These associations attenuated greatly on lag 1 d or lag 2 d. Elemental carbon, organic carbon, nitrate, sulfate, arsenic, cadmium, chromium and nickel were consistently associated with reduced HRV parameters in both single-constituent models and constituent-PM2.5 models. CONCLUSION: Our study highlighted the key roles of traffic-related components of PM2.5 in inhibiting cardiac autonomic function.