Short-term exposure to particulate matter on heart rate variability in humans: a systematic review of crossover and controlled studies

As an indicator of cardiac autonomic function, heart rate variability (HRV) has been proven to decrease after short-term exposure to particulate matters (PM) based on controlled animal studies. In this study, we conducted a systematic review to investigate short-term effects of exposure with different particle sizes on HRV in humans. Both crossover and controlled studies of human which were published prior to February 2020 were searched on four electronic databases. The HRV parameters included standard deviation of normal-to-normal intervals (SDNN), root mean square of successive normal-to-normal intervals (RMSSD), percent of normal-to-normal intervals that differ by more than 50 milliseconds (PNN50), low frequency (LF), high frequency (HF), and LF/HF. This review included 14 studies with 300 participants. The short-term effects of PM exposure on HRV in humans are inconclusive. For time-domain parameters, one study showed higher SDNN values with 2-h exposure to PM, whereas another one showed lower SDNN values. One study found RMSSD increased after PM exposure. One study found PNN50 decreased after PM exposure. For frequency-domain parameters, two studies showed LF increased with 2-h exposure to PM, and two studies showed an increase of LF/HF after PM exposure. Four studies showed lower HF values after PM exposure, whereas two studies showed higher HF values. Five studies did not find statistically significant results for any HRV parameters. We could not conclude that short-term exposure to PM can influence autonomic nervous function. The inconsistent changes of HRV in response to PM exposure may have complex mechanisms, which remains to be elucidated.