TY - JOUR
T1 - Principal stratification analysis to determine health benefit of indoor air pollution reduction in a randomized environmental intervention in COPD
T2 - Results from the CLEAN AIR study
AU - Woo, Han
AU - Koehler, Kirsten
AU - Putcha, Nirupama
AU - Lorizio, Wendy
AU - McCormack, Meredith
AU - Peng, Roger
AU - Hansel, Nadia N.
N1 - Funding Information:
The Clinical Trial of Air Cleaners to Improve Indoor Air Quality and COPD Health (CLEAN AIR) was supported by National Institute of Environmental Health Sciences grant [ R01ES022607 ]. The authors thank Austin Air Cleaners for the donation of air cleaners used in this trial. The company did not have any input on study design, analysis, or manuscript preparation.
Publisher Copyright:
© 2023 The Authors
PY - 2023/4/10
Y1 - 2023/4/10
N2 - Background: Indoor air quality represents a modifiable exposure to Chronic Obstructive Pulmonary Disease (COPD) health. In a randomized controlled trial (CLEAN AIR study), air cleaner assignment had causal effect in improving COPD outcomes. It is unclear, however, what is the treatment effect among those for whom intervention reduced air pollution and whether it was reduction in fine particulate matter (PM2.5) or nitrogen dioxide (NO2) that contributed to such improvement. Because pollution is a posttreatment variable, treatment effect cannot be assessed while controlling for pollution using intention-to-treat (ITT) analysis. Objective: Using principal stratification method, we assess indoor pollutants as the intermediate variable, and determine the causal effect of reducing indoor air pollution on COPD health. Method: In randomized controlled trial, former smokers with COPD received either active or placebo HEPA air cleaners and were followed for 6 months. Saint George's Respiratory Questionnaire (SGRQ) was the primary outcome and secondary measures included SGRQ subscales, COPD assessment test (CAT), dyspnea (mMRC), and breathlessness, cough, and sputum scale (BCSS). Indoor PM2.5 and NO2 were measured. Principal stratification analysis was performed to assess the treatment effect while controlling for pollution reduction. Results: Among those showing at least 40 % PM2.5 reduction through air cleaners, the intervention showed improvement in respiratory symptoms for the active (vs. placebo), and the size of treatment effect shown for this subgroup was larger than that for the overall sample. In this subgroup, those with active air cleaners (vs. placebo) showed 7.7 points better SGRQ (95%CI: −14.3, −1.1), better CAT (β = −5.5; 95%CI: −9.8, −1.2), mMRC (β = −0.6; 95%CI: −1.1, −0.1), and BCSS (β = −1.8; 95%CI: −3.0, −0.5). Among those showing at least 40 % NO2 reduction through air cleaners, there was no intervention difference in outcomes. Conclusion: Air cleaners caused clinically significant improvement in respiratory health for individuals with COPD through reduction in indoor PM2.5. Trial registration: ClinicalTrials.gov:
AB - Background: Indoor air quality represents a modifiable exposure to Chronic Obstructive Pulmonary Disease (COPD) health. In a randomized controlled trial (CLEAN AIR study), air cleaner assignment had causal effect in improving COPD outcomes. It is unclear, however, what is the treatment effect among those for whom intervention reduced air pollution and whether it was reduction in fine particulate matter (PM2.5) or nitrogen dioxide (NO2) that contributed to such improvement. Because pollution is a posttreatment variable, treatment effect cannot be assessed while controlling for pollution using intention-to-treat (ITT) analysis. Objective: Using principal stratification method, we assess indoor pollutants as the intermediate variable, and determine the causal effect of reducing indoor air pollution on COPD health. Method: In randomized controlled trial, former smokers with COPD received either active or placebo HEPA air cleaners and were followed for 6 months. Saint George's Respiratory Questionnaire (SGRQ) was the primary outcome and secondary measures included SGRQ subscales, COPD assessment test (CAT), dyspnea (mMRC), and breathlessness, cough, and sputum scale (BCSS). Indoor PM2.5 and NO2 were measured. Principal stratification analysis was performed to assess the treatment effect while controlling for pollution reduction. Results: Among those showing at least 40 % PM2.5 reduction through air cleaners, the intervention showed improvement in respiratory symptoms for the active (vs. placebo), and the size of treatment effect shown for this subgroup was larger than that for the overall sample. In this subgroup, those with active air cleaners (vs. placebo) showed 7.7 points better SGRQ (95%CI: −14.3, −1.1), better CAT (β = −5.5; 95%CI: −9.8, −1.2), mMRC (β = −0.6; 95%CI: −1.1, −0.1), and BCSS (β = −1.8; 95%CI: −3.0, −0.5). Among those showing at least 40 % NO2 reduction through air cleaners, there was no intervention difference in outcomes. Conclusion: Air cleaners caused clinically significant improvement in respiratory health for individuals with COPD through reduction in indoor PM2.5. Trial registration: ClinicalTrials.gov:
KW - Air cleaners
KW - COPD
KW - Environment
KW - Particulate matter
KW - Principal stratification
KW - Randomized controlled trial
UR - http://www.scopus.com/inward/record.url?scp=85148679006&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85148679006&partnerID=8YFLogxK
U2 - 10.1016/j.scitotenv.2023.161573
DO - 10.1016/j.scitotenv.2023.161573
M3 - Article
C2 - 36669663
AN - SCOPUS:85148679006
SN - 0048-9697
VL - 868
JO - Science of the Total Environment
JF - Science of the Total Environment
M1 - 161573
ER -