Ultra-short-term effects of fine particulate matter (PM2.5) exposure on heart rate variability in susceptible and vulnerable individuals using real-time personal monitoring

While epidemiological studies have examined the effects of exposure to particulate matter with diameter ≤2.5 μm (PM2.5) on heart rate variability (HRV) on a daily basis, there is a need for more granular data to better understand the ultrashort-term effects of PM2.5 on HRV. This study aimed to investigate the minute-level association between PM2.5 exposure and HRV using real-time personal monitoring data, focusing on time-lagged effects in vulnerable populations. We collected minute-by-minute data of PM2.5 and HRV using a wearable device from 73 individuals , with 3 days of continuous observations per participant (total 315,360 observations). PM2.5 and electrocardiogram (ECG)-derived HRV indices, including the standard deviation of normal-to-normal intervals (SDNN) and the root mean square of successive differences (RMSSD), were continuously measured for five days using wearable devices. Distributed lag non-linear and linear mixed-effects models were used to evaluate exposure-response relationships. PM2.5 exposure was significantly associated with acute HRV reductions within 180 min. SDNN decreased by -8.04% (95% CI: -11.10% to -4.88%) at the initial lag following exposure, peaking at approximately 49 minutes and gradually attenuating thereafter, and RMSSD decreased by -4.17% (95% CI: -7.23% to -1.00%) at the initial lag, with a similar attenuation pattern beyond 38 minutes. More pronounced effects occurred during nighttime (18:00-06:00), with SDNN decreasing by -13.9% (95% CI: -17.81% to -9.80%) and RMSSD by -7.43% (95% CI: -11.13% to -3.57%). Females exhibited a more immediate HRV decline at the initial lag (SDNN: -10.24%, RMSSD: -6.39%) compared to males (SDNN: -4.44%, RMSSD: -8.61%). Patients with arrhythmia showed the greatest reductions at the initial lag (SDNN: -11.42%, RMSSD: -15.95%). This study highlights the immediate autonomic impact of PM2.5 exposure, emphasizing its differential effects by time of day, sex, and health status. Findings underscore the importance of personal air pollution monitoring and targeted interventions for high-risk populations.