Indoor particulate matter and lung function in children

Abstract

People generally spend more time indoors than outdoors resulting in a higher proportion of exposure to particulate matter (PM) occurring indoors. Consequently, indoor PM levels, in contrast to outdoor PM levels, may have a stronger relationship with lung function. To test this hypothesis, indoor and outdoor PM_2.5 and fungal spore data were simultaneously collected from the homes of forty-four asthmatic children aged 10-16 years. An optical absorption technique was utilized on the collected PM_2.5 mass to obtain concentrations of black carbon (BC) and ultraviolet light absorbing particulate matter, (UVPM; a marker of light absorbing PM_2.5 emitted from smoldering organics). Enrolled children completed spirometry after environmental measurements were made. Given the high correlation between PM_2.5, BC, and UVPM, principal component analysis was used to obtain uncorrelated summaries of the measured PM. Separate linear mixed-effect models were developed to estimate the association between principal components of the PM variables and spirometry values, as well as the uncorrelated original PM variables and spirometry values. A one-unit increase in the first principal component variable representing indoor PM (predominantly composed of UVPM and PM_2.5) was associated with 4.1% decrease (99% CI = -6.9, -1.4) in FEV₁/FVC ratio. 11.3 μg/m³ increase in indoor UVPM was associated with 6.4% and 14.7% decrease (99% CI = -10.4, -2.4 and 99% CI = -26.3, -2.9, respectively) in percent predicted FEV₁/FVC ratio and FEF_25-75 respectively. Additionally, 17.7 μg/m³ increase in indoor PM_2.5 was associated with 6.1% and 12.9% decrease (99% CI = -10.2, -1.9 and 99% CI = -24.9, -1.0, respectively) in percent predicted FEV₁/FVC ratio and FEF_25-75, respectively. Outdoor PM, indoor BC, and indoor fungal spores were not significantly associated with lung function. The results indicate that indoor PM is more strongly associated with lung function in children with asthma as compared with outdoor PM.

Keywords: Asthmatic children; Indoor particles; Light absorbing particles; Lung function; Outdoor particles.

Figure 1:

Correlation plots of the mean concentrations of measured indoor particulate matter in each home (n = 43). r = Spearman correlation coefficient, UVPM = ultraviolet light absorbing particulate matter (light absorbing PM_2.5 emitted from smoldering organics such as smoking cigarettes and burning fireplace wood), BC = black carbon, PM_2.5 = particulate matter with aerodynamic diameter ≤ 2.5 μm, Fungi = fungal spore equivalents per cubic meter (SE/m³).

Figure 2:

Indoor/outdoor ratios of UVPM and PM_2.5 stratified by presence of smoker in the residence. P-values obtained from Tukey’s HSD test (controlling for repeated measures). From below, horizontal line in boxplot represents minimum (excluding outliers), 25^th, 50^th, 75^th percentiles and maximum (excluding outliers); Circles = outliers. Smoker home (n=12) = a home where at least one occupant smokes at least one cigarette per day, non-smoker home (n=59) = a home where no occupant smoked.

Figure 3:

Boxplots of the spirometry results from the 71 observations. FEV₁ = Forced expiratory volume in 1 second, FVC = Forced vital capacity, FEV₁/FVC ratio is the value obtained from dividing FEV₁ by FVC and multiplying by 100, FEF_25-75 = Forced expiratory flow at 25 – 75% of the FVC. From below, horizontal line in boxplot represents minimum (excluding outliers), 25^th, 50^th, 75^th percentiles and maximum (excluding outliers); Circles = outliers.

Figure 4:

Results of regression models developed to explore the association between 48-hour measurements of particulate matter (indoor and outdoor simultaneously) and percent predicted FEV₁/FVC ratio (adjusted for age, height, gender, and race). Dots= regression estimates; error bars = 99% CI = 99% confidence interval of regression estimate (adjusted for presence/absence of pets and family income). * indicates statistically significant finding, BC = black carbon, UVPM = ultraviolet light absorbing particulate matter, PC components = principal components of BC, UVPM, PM_2.5 and fungal spores. In Figures 4C – 4H, one standard deviation increase in BC, UVPM, PM_2.5, and fungal spores are associated with the corresponding regression estimates in the Figures. Four different models are presented to avoid multicollinearity of UVPM, BC, and PM_2.5.

Figure 5:

Results of regression models developed to explore the association between 48-hour measurements of particulate matter (indoor and outdoor) and percent predicted forced expiratory flow between 25 – 75% of the forced vital capacity (FEF_25-75) [adjusted for age, height, gender, and race], regression estimates are adjusted for adjusted for presence/absence of pets and family income. In Figures 5C – 5H, one standard deviation increase in BC, UVPM, PM_2.5, and fungal spores are associated with the corresponding regression estimates in the Figures. See Figure 4 footnotes for additional figure descriptions.