EFFECTS OF NITROGEN DIOXIDE ON HEART RATE VARIABILITY

Abstract

ISEE-14 Introduction: Although many studies have shown decrease in heart rate variability (HRV) was associated with particulate air pollutants, relatively few studies have investigated its association with gaseous air pollutants. Objective: This study was to examine the relationship between nitrogen dioxide (NO2) and HRV in the elderly population. Methods: We used a panel study to investigate short-term effects of air pollution on HRV. Our study subjects are 83 patients (mean age 61) from the cardiology section, Department of Internal medicine, National Taiwan University Hospital in Taipei. Continuous ambulatory electrocardiographic (ECG) monitoring was performed on each study subject, which measured time and frequency domains of HRV, such as standard deviation of normal-to-normal (NN) intervals (SDNN) and the square root of the mean of the squared differences between adjacent NN intervals (r-MSSD), high frequency (HF, 0.15-0.40 Hz) low frequency (LF, 0.04-0.15 Hz). NO2 and other co-pollutants, such as sulfur dioxide (SO2), carbon monoxide (CO), ozone, PM10 (particulate matter less than 10 um in diameter) and PM2.5 (particulate matter less than 2.5 um in diameter) measured at each subject’s close-by monitoring stations were used to represent personal exposure. We used linear mixed-effects models in single pollutant and multiple pollutant models to estimate the relationship between air pollution and log10-transformed HRV. Potential confounders, such as subject’s age, sex, body mass index (BMI), disease status of coronary heart diseases, smoking status, and ambient temperature were also adjusted in all models. Results: Single pollutant models showed that NO2 is the most consistent air pollutants responsible for both time and frequency domains of HRV decreases among all air pollutants. Such effects occurred at 1 to 4-hour moving averages. CO is also responsible for decreases in SDNN, r-MSSD, LF, and HF at 1-hour moving CO average. By contrast, we found no associations between HRV and PM2.5, PM10, SO2, or ozone. Multiple pollutant models with NO2 and CO further showed that NO2 was responsible for SDNN decreases at 1 to 4-hour moving NO2 average after controlling confounders. The models showed a 1ppb increase in NO2 exposure with 1-4 hour moving averages was associated 0.08-0.17% decreases in SDNN. Discussion: Our findings suggested that exposures to traffic-related air pollutants in urban environment, such as NO2 or CO, are associated with decreased HRV in susceptible population.