Inside or Outside, Air Quality Affects COPD Symptoms

ABERDEEN, Scotland, Aug. 31 -- COPD patients may be as much at risk from air pollution inside their homes as they are outside, researchers found.
Fine particulate pollution levels in the homes of COPD patients reached on average of up to four times higher than the maximum recommended by the U.S. Environmental Protection Agency, in a study reported in the Sept. 1 issue of the American Journal of Respiratory and Critical Care Medicine.
The higher levels-mainly from secondhand smoke-were significantly linked to greater symptom burden (P<0.01), said Liesl M. Osman, Ph.D., of the Aberdeen Royal Infirmary here, and colleagues.
Outdoor air quality, including particulate matter levels, have been well documented to have an impact on respiratory mortality and hospital admissions, they said.
But, "indoor air quality has assumed greater importance for health," commented Mark D. Eisner, M.D., M.P.H., of the University of California, San Francisco, in an accompanying editorial.
"Residents of developed countries spend the majority of their time indoors, which provides more potential for indoor exposures," he said. "At the same time, changes in home and office building construction have resulted in lower air exchange rates, increasing personal exposure to pollutants emitted indoors."
To determine the effect of indoor air quality, the researchers studied COPD patients in northeast Scotland as part of the larger HEARTH (Home Environment and Respiratory Health) Study evaluating the impact of home improvement intervention on respiratory health.
The analysis included 148 participants with confirmed COPD in the initial cross-sectional component of the study before the intervention.
Participants' mean lung function (forced expiratory volume in one second, FEV1) was 43% of that predicted. The majority (61%) had moderate disease by GOLD (Global Initiative for Chronic Obstructive Lung Disease) criteria, whereas 26% had severe and 12% had mild COPD.
Among the participants, 58% were nonsmokers at the time of the baseline questionnaire, but 73% lived in a household where at least one member smoked.
The investigators monitored levels of particulate matter with a diameter of 2.5 µm or less in participants' living rooms over at least a 12-hour period from afternoon through to midmorning the next day.
They found the average particulate matter level overall was 18 µg/m3 whereas the mean peak was 155 µg/m3.
Particulate matter levels were substantially higher for smoking households (average 71 µg/m3, median maximum 453 µg/m3).
Even in nonsmoking households, though, levels peaked at about the same maximum as in the smoking households over short periods, which Dr. Osman and colleagues attributed to visiting smokers.
On multivariate analysis, increasing levels of airborne particulates were significantly associated with worse COPD symptom scores reported on the St. George's Respiratory Questionnaire for average and maximum levels alike (both P=0.002).
A 10-fold decrease in average or maximum indoor particulate matter was estimated to significantly decrease symptom score by 5.3 and 6.0 points, respectively (P=0.001). A four-point change is considered clinically significant, the researchers noted.
Interestingly, particulate matter had a stronger effect on symptom burden of current smokers than of nonsmokers as reflected in larger regression coefficients.
Thus, a 10-fold reduction in average particulate matter would be expected to reduce symptoms by 11.1 points in smokers versus 4.9 points in nonsmokers, and the change in particulate matter needed to produce a clinically significant four-point change was correspondingly smaller among smokers.
But, "the apparently greater effect among smokers may be an artifact of the higher levels of PM2.5 in their homes," Dr. Osman and colleagues wrote.
Two other components of indoor air pollutant, endotoxin and nitrogen dioxide, were measured in participants' homes. However, neither was a significant predictor for any of the outcomes evaluated.
Further research is needed to test the long-term impact of indoor air quality on COPD patients as well as to determine whether indoor pollutant exposure increases frequency of exacerbations, the investigators said.
The authors also pointed out that the study was cross-sectional in design and health status was related to indoor environment measurement taken at one point in time.
But even though researchers could not prove causality, "because they used an objective measure of secondhand smoke exposure, these results provide strong new evidence linking secondhand smoke with worse COPD health status," Dr. Eisner concluded.
The study was supported by the Eaga Partnership Charitable Trust. Neither the researcher nor Dr. Eisner reported any relevant financial conflicts of interest. Primary source: American Journal of Respiratory and Critical Care MedicineSource reference: Osman LM, et al "Indoor Air Quality in Homes of Patients with Chronic Obstructive Pulmonary Disease" Am J Respir Crit Care Med 2007;176:465-472. Additional source: American Journal of Respiratory and Critical Care MedicineSource reference: Eisner MD "Indoor Air, Passive Smoking, and COPD" Am J Respir Crit Care Med 2007;176:426-427.