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SAO PAULO, Brazil -- Women who are on long-term oxygen therapy for chronic obstructive pulmonary disease (COPD) are 54% more likely to die than men.
SAO PAULO, Brazil, Sept. 1 -- Women who are on long-term oxygen therapy for chronic obstructive pulmonary disease (COPD) have an increased risk of death, compared with men, according to researchers here.
In a seven-year prospective study, women referred to oxygen therapy were 54% more likely to die than were men, Maria-Christina Machado, M.D., Ph.D., of the State Public Hospital, and colleagues, reported in the first September issue of the American Journal of Respiratory and Critical Care Medicine.
Dr. Machado and colleagues followed 435 oxygen-dependent patients with COPD, 184 of them women. The clinical management for COPD for both groups was similar and was based on the latest treatment guidelines, Dr. Machado said.
"Interestingly, we found that men and women exhibited similar survival rates during the initial follow-up period," she said. "Differences in survival became more apparent only after three years of follow-up."
In univariate analyses, the researchers found a non-significant trend for women to die more quickly. But when the researchers adjusted for possible confounding factors, such as cigarette smoking, age, arterial oxygen pressure (PaO2), lung function (FEV1), and body mass index, the trend became significant, Dr. Machado and colleagues reported.
In the multivariate analysis, women's hazard ratio for death was 1.54, with a 95% confidence interval from 1.15 to 2.07, which was significant at P=0.004. Other independent predictors of death were arterial oxygen pressure and body mass index, significant at P<0.001 and P<0.05, respectively, the researchers found.
Women in the study were younger and reported fewer pack-years of cigarette smoking than the men, but they had similar impairments in lung function and oxygenation, the researchers said, suggesting they may be more susceptible to COPD.
In an accompanying editorial, David Mannino, M.D., of the University of Kentucky Medical Center in Lexington said the gender-mortality question remains open. He called for studies of other cohorts, with "careful analysis from both clinical data and observational trials."
He noted that the Brazilian study had some potential biases:
If the excluded population was similar for men and women, he added, "it is of interest that the women in the study were significantly younger than the men, suggesting that women treated for COPD in this hospital had developed COPD at an earlier age than men."
Dr. Machado and all but one of her co-authors said they had no financial link with any company that has an interest in COPD. The other co-author has served on advisory boards for several pharmaceutical firms.
Dr. Mannino reported serving on advisory board for several pharmaceutical firms and receiving research grants from GlaxoSmithKline and Pfizer.