Among patients on long-term oxygen therapy for chronic obstructive pulmonary disease (COPD), women are more likely to die from the disease than men.
This study appears in the first issue for September 2006 of the American Journal of Respiratory and Critical Care Medicine, published by the American Thoracic Society.
Maria-Christina L. Machado, M.D., Ph.D., of the State Public Hospital of São Paulo in Brazil, and seven associates assessed 435 oxygen-dependent patients with COPD. Of the group, 184 women and 251 men were observed while on long-term oxygen therapy over a seven-year period.
After considering such factors as age, pack-years smoked, lung function test results and weight, investigators found females to be at a significantly higher risk for death from the disease.
"We found that women had a 54 percent increase in the risk of death after initiating long-term oxygen therapy compared with the men," said Dr. Machado.
The primary risk factor for developing COPD is smoking. The illness is characterized by chronic bronchitis and severe emphysema, which frequently co-exist, obstructing airflow to the lungs and interfering with normal breathing.
COPD is the fourth leading cause of death in the U.S., and the fifth in Brazil. In 2002, 10.7 million U.S. adults were estimated to have this debilitating disease. In 2004, the cost to the nation for COPD was $37.2 billion in direct and indirect health care costs.
"The only therapeutic regimen that has been shown to improve life expectancy in these patients is oxygen therapy," said Dr. Machado. "Interestingly, we found that men and women exhibited similar survival rates during the initial follow-up period. Differences in survival became more apparent only after three years of follow-up. The clinical management for COPD for both groups was similar and was based on the latest treatment guidelines."
The researchers noted previous research has shown that women who smoke had a greater decrease in basic lung function test results in comparison to men who smoke, suggesting a possible increased susceptibility to the development of COPD.
Prior studies also show that COPD affects other organ systems, as well as the lungs. For example, individuals who smoke and develop COPD further increase their risk of cardiovascular disease.
In an editorial on the research published in the same issue of the journal, David M. Mannino, M.D., of the University of Kentucky Medical Center, wrote: "One explanation for worse survival among women might be that some of the systemic complications of COPD, such as muscle dysfunction or depression, are more common in women and that these lead to worse outcomes."
"In two recently published studies of COPD, women had almost three times the prevalence of depression as men (38 percent versus 13 percent) and twice the prevalence of fat-free body mass depletion (40 percent versus 20 percent). While we do not know whether these complications were increased in the study by Dr. Machado and colleagues, it is plausible that the observed differences may have been related to these or other COPD-related complications that differ between the sexes."
He concluded: "Does sex influence survival in COPD? This is still an open question. This study suggests that women with COPD who are on oxygen may die more quickly than men. Whether this observation holds true in other cohorts with differing severity of COPD is yet to be determined. Careful analysis from both clinical data and observational trials will shed more light on this important question and, it is hoped, provide guidance for how to better intervene in the care of our patients with COPD."
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