UFP exposure and biomarkers of exposure/effect on small airways in school children

Abstract

Background/Aim Ultrafine particles (UFP) are of health concern due to their small size and ability to diffuse into the circulatory system once inhaled. However, epidemiological studies of adverse respiratory effects from UFP exposure are uncommon and evidence is varied. There is a scarcity of data on its effects on small airways. We aimed to study associations between UFP exposure and markers of small airways exposure/impacts in school children. Methods We used a time-integrated model for particle number count (PNC) (UFP indicator), which combined measurements at schools and modelled PNC at home using land use and time trends, to assign annual average daily exposure. We measured biomarkers of small airways exposure/impact: respiratory system resistance (Rrs); respiratory system reactance (Xrs); and lung clearance index (LCI); in 577 children recruited from 25 schools. We estimated the effect of exposure to PNC on these outcomes using Bayesian generalised linear mixed effects regression models. Analyses adjusted for potential confounders, using three models: 1) age, sex, height; 2) Model 1 plus BMI, home air conditioning, carpet, garage, gas cooking, gas heating; home flooded or with visible mould (<12 months); blood cotinine levels (ETS); 3) Model 2 plus PM2.5 mass (24 h prior to clinical testing) and annual average daily NO2 exposure. Results The PNC model explained 26% of the variability of PNC measured at the schools. No statistically significant associations were observed between PNC and LCI or Xrs. Protective statistically significant associations were observed for respiratory resistance in Models 1 and 2, but not 3. Conclusions These results do not demonstrate a detrimental effect of UFP on biomarkers of small airways exposure/impact, and the results for resistance (reflecting airway calibre) are counter-intuitive to expected. This might be due to the low predictive capacity of the exposure model, therefore improved exposure measures are needed in future studies.