Reducing the exposure to fine particles in living spaces using an air filtration device may improve airway mechanics, airflow limitation, and inflammation in children with asthma, according to a study published in JAMA Pediatrics.

This was a randomized, double-blind, crossover study conducted during a low-ozone season in children with mild or moderate asthma treated at an outpatient clinic of the Shanghai General Hospital, Shanghai, China. The investigators sought to determine whether the use of a fine particle (particulate matter 2.5 µm in size [PM2.5]) filtration device in the bedrooms of children with asthma had an effect on pathophysiologic changes observed in the small airways of these patients.

A total of 43 children (ages, 5-13 years; 60.4% boys) were enrolled. A true filtration device and a sham filtration device were installed in the bedrooms of study participants in a random order for 2 weeks, with a 2-week washout interval between each period. The concentrations of PM2.5 and ozone were measured inside the bedrooms and outside the window. The primary study outcome was fractional exhaled nitric oxide (FeNO). Secondary outcomes included spirometry, impulse oscillometry, and peak expiratory flow indicators.

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 The baseline forced expiratory volume in 1 second (FEV1) levels were >80% of the expected value in 93% of participants. Nine participants had FeNO values >35 ppb, suggesting eosinophilic airway inflammation, and 13 had blood eosinophilic counts >450 cells/µL.

Daily mean concentrations of outdoor PM2.5 ranged from 28.6 µg/m3 to 69.8 µg/m3. Maximum ozone levels ranged from 7.7 ppb to 98.3 ppb. Outdoor concentrations of PM2.5 and ozone were comparable between the periods of filtration vs sham device use.

When true filtration was used, bedroom PM2.5 concentrations were a mean of 63.4± 35.9% lower than with sham filtration. True vs sham filtration was associated with improved airway mechanics, as indicated by a 24.4% decrease in total airway resistance (95% CI, 11.8%37.1%), a 43.5% reduction in small airway resistance (95% CI, 13.7%-73.3%), and a 73.1% increase in airway reactance (95% CI, 0.3%-145.8%).

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The use of true filtration was also associated with improvements in FeNO (27.6% reduction; 95% CI, 8.9%-42.4%) and peak expiratory flow (1.6% increase, from 253.5 L/min to 245.1 L/min). In addition, significant improvements in small airway function were observed in patients who did not have any eosinophilic airway inflammation at baseline (P =.03).

“These observations support a future clinical trial to assess the efficacy and effectiveness of indoor air filtration in improving small airway pathophysiology that plays a vital role in asthma,” concluded the study authors.


Cui X, Li Z, Teng Y, Barkjohn KK, et al. Association between bedroom particulate matter filtration and changes in airway pathophysiology in children with asthma [published online April 6, 2020]. JAMA Pediatr. doi: 10.1001/jamapediatrics.2020.0140