The study, led by Fernando J. Martinez, M.D., of the University of Michigan, was reported in the August 1, 2007 issue of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
The investigators analyzed 1053 randomized patients--38.8 percent of whom were female--from 17 National Emphysema Treatment Trial (NETT) clinics. Patients were selected for severe chronic airflow obstruction and an emphysematous phenotype. They then compared symptomatic, physiological, radiological and histological data between men and women.
"From a public health perspective, the investigation of sex and gender differences in COPD in timely, because in 2000, the number of women with COPD surpassed the number of men," noted Dawn L. DeMeo, M.D., M.P.H., of Brigham and Young Women's Hospital in the accompanying editorial.
Women in the study had shorter smoking histories and lower body mass index than men, and experienced more breathlessness, lower lung function and decreased exercise capacity compared to men. They also reported more depression, a lower quality of well-being and scored more poorly on a test for overall mental health.
Radiological assessment showed that women had less extensive emphysema than men, with smaller emphysematous lesions. Histological analysis of lung tissue in 101 patients showed that women airways with thicker walls, and disproportionately reduced airway lumens in comparison to men.
However, even after controlling for age, FEV1% predicted (a standard measure of lung function), smoking history and severity of emphysema, the researchers found that women reported more breathlessness, higher depression, lower mental health and lower overall quality of life than men.
"These data showing greater breathlessness in women relative to men at similar degrees of airflow obstruction and emphysema severity imply that sex-specific anatomic differences must be considered in models of COPD pathogenesis," the researchers wrote.
The fact that women in the study exhibited similarly severe COPD to men but had shorter smoking histories raises some important questions about the nature and progression of COPD with regard to sex. "Are women more predisposed to have more airway disease," asked Dr. DeMeo. "Do women with similarly severe disease ... do worse clinically because of the physiologic impact of having more airway disease" Or is it that women have more systemic sequelae related to COPD, as manifested by higher prevalence of depression, decreased functional capacity and more body mass loss""
It may also suggest that some sex differences in COPD could reflect social and cultural issues. The women's poorer health status, lower quality of well-being and greater depression than men might influence their subjective experience of their symptoms or even the manifestations of the symptoms themselves. "Our data cannot provide a mechanistic explanation for the reported differences, but suggest additional investigation in this area is required," the investigators reported.
The study should be considered "hypothesis generating," they said. "Our data should motivate future studies to determine the complex interactions between biological and socio-cultural factors that contribute to these differences, and thus to provide a foundation for novel therapies to reduce the increasingly disproportionate burden of this common disease in women," concluded the researchers.