Influence of Dose Metrics on Associations between Exposure to Black Carbon and Exhaled Nitric Oxide in Children with Asthma

Abstract

BACKGROUND AND AIM: Few studies examined the associations between fractional exhaled nitric oxide (FeNO) and traffic-related air pollution (TRAP) from individual dosimetry models. Our study aimed to assess the associations between FeNO and black carbon (BC, as a surrogate of TRAP) from four dose metrics. Besides, we aimed to examine if more refined dose metrics would impact the health risk estimates. METHODS: We recruited 35 children with asthma living in environmental justice communities. Daily FeNO measurements were followed for up to 30 days for each child. Four dose metrics were calculated based on measurements from a central-site and personal monitors, with and without estimates of inhalation rates based on a self-reported time-activity questionnaire. Linear mixed effect models were used to test the associations of BC at different lag periods and FeNO. RESULTS:Exposure to BC was positively associated with FeNO within the first 24 hours of exposure. A log-transformed interquartile range increase in inhaled dose from metrics that used central-site estimates (Model A, C) increased 7% (95% CI: 1% - 14%) and 6% (95% CI: 0% - 13%) in FeNO at lag 0-6 hours in the adjusted model 4. The strength of association persisted at lag 7-12 hours and then decreased and became insignificant at longer lag periods. Similarly, the inhaled dose from personal monitored estimates (Model B, D) was positively associated with FeNO within the first 24 hours. Using personal BC measurements or dynamic inhalation rate did not improve prediction of changes in FeNO. CONCLUSIONS:Our findings revealed that inhaled BC dose significantly increases FeNO level within the first 24 hours of exposure. Our results provide evidence that personal exposure to BC was associated with airway inflammation among children with asthma. Our results also add to the limited number of studies that compared the effect estimates among alternative dose metrics within a single study. KEYWORDS: traffic-related, air pollution, Short-term exposure, asthma, Children's environmental health