Association Between Bedroom Particulate Matter Filtration and Changes in Airway Pathophysiology in Children With Asthma

Abstract

Importance: Fine particles (particulate matter 2.5 μm [PM2.5]), a ubiquitous air pollutant, can deposit in the small airways that play a vital role in asthma. It appears to be unknown whether the use of a PM2.5 filtration device can improve small airway physiology and respiratory inflammation in children with asthma.

Objective: To discover what pathophysiological changes in the small airways are associated with using a PM2.5-removing device in the bedrooms of children with asthma.

Design, setting, and participants: Children with mild or moderate asthma were enrolled in this double-blind, crossover study. The participants used a true filtration device and a sham filtration device in their bedrooms in a random order for 2 weeks each with a 2-week washout interval. The study was conducted in a suburb of Shanghai, China, during a low-ozone season.

Exposures: Ozone and PM2.5 were measured inside bedrooms and outside a window.

Main outcomes and measures: Impulse oscillometry, spirometry, and fractional exhaled nitric oxide were measured at the beginning and the end of each intervention. Peak expiratory flow was measured twice daily at home.

Results: Forty-three children (5-13 years old; 26 boys [60%]) participated. Outdoor 24-hour mean PM2.5 concentrations were moderately high, ranging from 28.6 to 69.8 μg/m3 (median, 53 μg/m3). During true filtration, bedroom PM2.5 concentrations were a mean (SD) of 63.4% (35.9%) lower than during sham filtration. Compared with sham filtration, true filtration was significantly associated with improved airway mechanics, reflected in a 24.4% (95% CI, 11.8%-37.1%) reduction in total airway resistance, a 43.5% (95% CI, 13.7%-73.3%) reduction in small airway resistance, a 22.2% (95% CI, 2.2%-42.2%) reduction in resonant frequency, and a 73.1% (95% CI, 0.3%-145.8%) increase in airway reactance. True filtration was also associated with significant improvements in fractional exhaled nitric oxide (a 27.6% [95% CI, 8.9%-42.4%] reduction) and peak expiratory flow (a 1.6% [95% CI, 0.8%-2.5%] increase). These improvements were significantly associated with bedroom PM2.5 reduction. Improvements in small airway function were nonsignificant (8.4% [95% CI, -1.4% to 18.3%]) in all participants but significant (13.2% [95% CI, 1.2%-25.1%]) in participants without eosinophilic airway inflammation at baseline. No improvements were observed for forced vital capacity, forced expiratory volume during the first second, and the ratio of these in all participants or subgroups.

Conclusions and relevance: Per these results, indoor PM2.5 filtration can be a practical method to improve air flow in an asthmatic lung through improved airway mechanics and function as well as reduced inflammation. This warrants a clinical trial to confirm.

Trial registration: ClinicalTrials.gov Identifier: NCT03282864.

Conflict of interest statement

Conflict of Interest Disclosures: Dr Cui reported grants from Underwriters Laboratories Inc and graduate student fellowship from Duke University during the conduct of the study. Drs Z. Li, Teng, Barkjohn, Norris, He, Lin, Wang, Zhou, and Bergin reported grants from Underwriters Laboratories Inc during the conduct of the study. Dr Barkjohn reported grants from Oak Ridge Institute for Science and Education outside the submitted work. Dr Mo reported grants from National Natural Science Foundation of China during the conduct of the study. No other disclosures were reported.

Figures

Figure 1.. CONSORT Diagram

Figure 2.. Pollutant Concentrations in Bedrooms and Outdoors by Filtration Status

Concentrations graphed were 2-week mean values. Statistical significance in median concentrations was determined using a Wilcoxon signed rank test. PM2.5 indicates particulate matter smaller than 2.5 μm.

Figure 3.. Outcomes Associated With True Filtration (vs Sham Filtration) and Bedroom Fine Particle (PM2.5) Exposure Reduction

A, Outcomes of true filtration compared with sham filtration. For all outcomes except peak expiratory flow (PEF), the points and bars show mean and 95% CIs for outcome improvements when comparing filtration changes in outcome levels between true filtration and sham filtration. For PEF, the point and the bar show the mean and 95% CIs when comparing PEF values measured during the true filtration period with PEF values measured during the sham filtration period. For all outcomes, positive values indicate improvements and negative values indicate deterioration. For fractional exhaled nitric oxide (FeNO) data, the analysis was performed on log-transformed FeNO data and the result was converted back to untransformed data for presentation in this figure. B, outcomes associated with bedroom fine particle (PM2.5) exposure reduction. Points and bars show mean and 95% CIs for outcome improvements associated with a 10-μg/m3 reduction in bedroom PM2.5 concentration from outdoor levels. For all indicators, positive values indicate improvements and negative values indicate deterioration. For fractional exhaled nitric oxide (FeNO) data, the analysis was performed on log-transformed FeNO data, and the result was converted back to untransformed data for presentation in this figure. FEF25-75 indicates forced expiratory flow during 25% to 75% of forced vital capacity; FEV1, forced expiratory volume during the first second; Fres, resonant frequency; FVC, forced vital capacity; PM2.5, particulate matter smaller than 2.5 μm; R5, airway resistance measured at 5 Hz; R20, airway resistance measured at 20 Hz; R5-R20, the difference between R5 and R20, reflecting small airway resistance; X5, airway reactance measured at 5 Hz.

Figure 4.. Outcomes of True Filtration vs Sham Filtration, Stratified by Baseline Eosinophilic Airway Inflammation, as Indicated by Baseline Fractional Exhaled Nitric Oxide (FeNO) or Blood Eosinophil Count

The FeNO cut point was 35 ppb. The blood eosinophil count cut point was 450 cells per μL (to convert to cells × 109, multiply by 0.001). For all outcomes except peak expiratory flow (PEF), the points and bars show mean and 95% CIs for outcome improvements when comparing the before-and-after filtration changes in outcome levels between true filtration and sham filtration. For PEF, the point and the bar show the means and 95% CIs when comparing PEF values measured during the true filtration period with PEF values measured during the sham filtration period. For all outcomes, positive values indicate improvements and negative values indicate deterioration. For FeNO data, the analysis was performed on log-transformed FeNO data, and the result was converted back to untransformed data for presentation in this figure. FEF25-75 indicates forced expiratory flow during 25% to 75% of forced vital capacity; FEV1, forced expiratory volume during the first second; Fres, resonant frequency; FVC, forced vital capacity; PEF, peak expiratory flow; R5, airway resistance measured at 5 Hz; R20, airway resistance measured at 20 Hz; R5-R20, the difference between R5 and R20, reflecting small airway resistance; X5, airway reactance measured at 5 Hz.