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 (PM_2.5) 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 PM_2.5 on HRV. This study aimed to investigate the minute-level association between PM_2.5 exposure and HRV using real-time personal monitoring data, focusing on time-lagged effects in vulnerable populations. We collected minute-by-minute data of PM_2.5 and HRV using a wearable device from 73 individuals, with 3 days of continuous observations per participant (total 315,360 observations). PM_2.5 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. PM_2.5 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 min 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 min. 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 PM_2.5 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.