Structural equation modeling of parasympathetic and sympathetic response to traffic air pollution in a repeated measures study

Abstract

BackgroundTraffic-related air pollution has been associated to a range of adverse health impacts, including decreased heart rate variability (HRV). The association between traffic-related pollution and HRV, however, has varied by traffic-related or HRV marker as well as by study, suggesting the need for a more comprehensive and integrative approach to examining air pollution-mediated biological impacts on these outcomes. In a Bayesian framework, we examined the effect of traffic pollution on HRV using structural equation models (SEMs) and looked at effect modification by participant characteristics.MethodsWe studied measurements of 5 HRV markers [high frequency (HF), low frequency (LF), 5-min standard deviation of normal-to-normal intervals (SDNN), square root of the mean squared differences of successive normal-to-normal intervals (rMSSD), and LF/HF ratio (LF/HF)] for 700 elderly men from the Normative Aging Study. Using SEMs, we fit a latent variable for traffic pollution that is reflected by levels of carbon monoxide, nitrogen monoxide, nitrogen dioxide, and black carbon (BC) to estimate its effect on latent variable for parasympathetic tone that included HF, SDNN and rMSSD, and the sympathetic tone marker, LF/HF. Exposure periods were assessed using 4-, 24-, 48-, 72-hour moving average pre-visit. We compared our main effect findings using SEMs with those obtained using linear mixed models.ResultsTraffic pollution was not associated with mean parasympathetic tone and LF/HF for all examined moving averages. In Bayesian linear mixed models, however, BC was related to increased LF/HF, an inter quartile range (IQR) increase in BC was associated with a 6.5% (95% posterior interval (PI): -0.7%, 14.2%) increase in mean LF/HF 24-hours later. The strongest association observed was for the 4-hour moving average (10.1%; 95% PI: 3.0%, 17.6%). The effect of traffic on parasympathetic tone was stronger among diabetic as compared to non-diabetic participants. Specifically, an IQR increase in traffic pollution in the 48-hr prior to the clinic visit was associated with a 44.3% (95% PI: -67.7%, -4.2%) lower mean parasympathetic tone among diabetics, and a 7.7% (95% PI: -18.0%, 41.4%) higher mean parasympathetic tone among non-diabetics.ConclusionsBC was associated with adverse changes LF/HF in the elderly. Traffic pollution may decrease parasympathetic tone among diabetic elderly.

Exposure to sub-chronic and long-term particulate air pollution and heart rate variability in an elderly cohort: the Normative Aging Study

“…We report discrepant findings for BC and PM 2.5 . The direction of results for modeled PM 2.5 exposure 1, 2, or 3 days prior to the study visit are consistent with previous fixed monitoring studies from the NAS [ 10 , 15 ] as well as with our findings for sub-chronic BC exposure. Air pollution was associated with decreased HF, LF, and SDNN as well as an increased LF:HF ratio in these studies.…”

“…We did not observe strong evidence of effect modification by obesity, hypertension, diabetes, or oxidative stress allelic profile, which may have been due to the low precision of stratified effect estimates. While not rising to the level of statistical significance, associations between BC exposure and HRV were somewhat stronger among men with obesity and diabetes, which is notable mainly because of similarity to previous findings [ 10 , 15 ]. One explanation for these findings is that diabetes and obesity are themselves associated with reduced autonomic function [ 42 – 44 ], possibly rendering diabetics and those with a BMI over 30 kg/m 2 more susceptible to the effects of particles on this same endpoint.…”

“…Because of previous research indicating potentially susceptible subgroups [ 10 , 15 ], we examined effect modification of the association between 28 day exposure to BC and HRV parameters by obesity (defined as BMI ≥ 30 kg/m 2 ; yes/no), hypertension (yes/no), diabetes (yes/no) and oxidative stress allelic profile (high/low; dichotomized based on median score) using separated linear regression models. We also included multiplicative interaction terms in regression models to evaluate effect modification.…”

“…Reduced HRV is predictive of increased cardiovascular morbidity and mortality risk [ 12 , 13 ]. Short-term particulate air pollution exposure is associated with reduced HRV in many epidemiologic studies, including a recent meta-analysis [ 14 ] and within the current study population [ 10 , 15 ]. Associations are particularly pronounced among the elderly [ 16 ], among those with preexisting cardiovascular disease or diabetes [ 17 ], or among people with reduced antioxidative defenses [ 17 , 18 ].…”

Short-term airborne particulate matter exposure alters the epigenetic landscape of human genes associated with the mitogen-activated protein kinase network: a cross-sectional study

“…The Normative Aging Study (NAS) is a longitudinal study of human aging in Eastern Massachusetts, established in 1963 by the Veterans Administration [ 13 , 33 – 36 ]. Community-dwelling men from the greater Boston metropolitan area were screened at entry and accepted into the study if they had no prior history of heart disease, hypertension, diabetes mellitus, cancer, peptic ulcer, gout, recurrent asthma, bronchitis, or sinusitis.…”