Personal PM2.5Exposure and Resting Heart Rate in the Study of Pollution and COPD Exacerbation (SPACE) Cohort

Abstract

BackgroundDaily changes in fine particulate matter (PM2.5) exposure have been linked to intermediate cardiovascular outcomes such as reduced heart rate (HR) variability and elevated HR. While less is known about PM exposure and resting HR, higher resting HR can indicate cardiovascular pathophysiology that may predict poor cardiovascular outcomes.MethodsWe recruited 27 former smokers with a clinical diagnosis of COPD and GOLD Stage II or greater airflow obstruction on spirometry residing in the Boston area. Participants were followed for up to 4 months (1 month per season), during which they wore Fitbit Charge 2 activity monitors and a personal air quality monitor by Atmospheric Sensors Ltd (ASL). We applied linear mixed effects models to examine associations between same- and previous-day PM2.5 and daily resting HR. We accounted for intra-individual correlations by using participant-specific random effects and nesting participants within observation month. Errors were assumed to follow a first-order autoregressive covariance structure. Models were adjusted for age, sex, race, BMI, COPD severity (FEV1), education, season, temperature, relative humidity, coronary artery disease, congestive heart failure, arrythmia, and nodal blocker use.ResultsA total of 2,120 observation-days were collected from the study participants, who were 44% female with mean (SD) age of 72 (8) years. 75% of the daily PM2.5 fell between 4-11 µg/m3 (mean=10 µg/m3). Daily resting HR was normally distributed with mean 70 bpm (SD=8.7). Same-day PM2.5 is not associated with resting HR when evaluated as a continuous variable, in quartiles, or as a binary variable relative to the EPA Air Quality Index 24-hour threshold of 12 µg/m3 (for “good” air quality). Previous-day PM2.5 was not associated with resting HR. Across all models, lower education level and arrythmia were associated with higher resting HR.ConclusionSame and previous-day personal PM2.5 exposure was not associated with daily resting HR in this population with moderate to severe COPD.