While the exacerbating effects of outdoor pollutants on COPD patients have been well-documented, few studies have analyzed the impact of indoor air quality on COPD patients. COPD is the fourth leading cause of death in the U.S., and the fifth worldwide, according to lead investigator Liesl M. Osman, Ph.D.
"Although exposure to outdoor pollution is important, most people spend the greater part of their time indoors," wrote Dr. Osman in the article that appears in the first issue for September of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
Dr. Osman and a team of researchers in Aberdeen, Scotland, measured concentrations of indoor air pollutants in the homes of 148 Scottish patients who had mild to severe COPD. Over the course of a week, they took samples of particulate matter up to 2.5́g (PM2.5) every five minutes, sampled indoor endotoxin concentrations and measured indoor NO2 with passive samplers. Recorded data on concentrations of outdoor PM2.5 were also collected from a nearby monitoring station.
The study participants completed the St. George's Respiratory Questionnaire (SGRQ) to assess their symptoms, activity limitation and the impact of their disease. Each subject was also asked about their current smoking status, which was verified by salivary cotinine levels.
The researchers found that indoor concentrations of particulate pollution in the subjects' homes frequently exceeded standards for outdoor air. In at least one instance, the highest concentration of a home was more than 40 times that of the recommended maximum.
"High levels of PM2.5 were recorded in the homes of patients with COPD," they wrote. "The highest levels of PM2.5 were, on average, four times the maximum recommended by the U.S. Environmental Protection Agency for 24 hour periods," they continued, noting that a significant source of PM2.5 was environmental tobacco smoke. Nearly 40 percent of the subjects were current smokers, and 17 percent of non-smokers lived in "smoking environments" where others smoked in their homes.
Both smokers and non-smokers were negatively affected by increased PM2.5, as measured by clinically significant differences in their SGRQ symptom scores. Interestingly, an analysis of the effect of indoor air quality on smokers versus non-smokers revealed that smokers suffered greater adverse effects that nonsmokers. No significant effects of NO2 or endotoxin levels were found.
While these findings may be an artifact of the higher overall levels of PM2.5 in the homes of smokers, the researchers noted that the data also illuminated a gap in the current knowledge on the lives of patients with COPD.
Previous studies of indoor air quality have tended to exclude smokers, which may have resulted in an overall underestimate of the impact of indoor air quality on health status, as well as painted an unrealistic picture of the COPD patient population.
"The finding that indoor PM2.5 concentrations had negative respiratory health effects among both smokers and nonsmokers has important implications for future research," wrote Mark D. Eisner, M.D., M.P.H., of the University of California, San Francisco, in an editorial in the same issue of the journal. "Further research is needed to elucidate the prospective effects of indoor air pollutants on adults with COPD."