The respective size of two major arteries, visible on a simple computed tomography, or CT, scan, is a strong predictor of the risk of exacerbation of chronic obstructive pulmonary disease, according to new research from the University of Alabama at Birmingham published online Sept. 3, 2012, in the New England Journal of Medicine.
The research team says that an increase in the size of the pulmonary artery relative to the size of the aorta is a valid indicator that a patient with COPD is at risk for exacerbating their disease. These exacerbations of COPD are associated with accelerated loss of lung function, worsened quality of life and increased risk of death.
In patients without lung disease, the aorta is typically a little larger than the pulmonary artery, according to Mark Dransfield, M.D., associate professor in the UAB Division of Pulmonary, Allergy and Critical Care Medicine and principal investigator of the study. The pulmonary artery may enlarge in patients with COPD for reasons including a rise in intravascular pressure due to the loss of lung tissue and associated difficulty in transferring oxygen to the bloodstream due to underlying heart disease, which is common in this population.
"Our findings indicate that when the pulmonary artery becomes larger than the aorta, regardless of the underlying cause or other health conditions, the risk of exacerbation increases," Dransfield says. "In particular, the risk of exacerbation requiring hospitalization increases dramatically."
Dransfield, who is the medical director of the UAB Lung Health Center, says exacerbations leading to hospitalization are expensive to treat, accounting for $18 billion in direct costs annually in the United States. Hospitalization also is associated with a 21 percent chance of death within one year and a 55 percent chance of death within five years.
The investigators analyzed data from 3,464 patients enrolled in the COPDGene® study, a multi-center, observational trial sponsored by the National Heart, Lung and Blood Institute, one of the National Institutes of Health, and 2005 patients enrolled in the Evaluation of COPD Longitudinally to Identify Predictive Surrogate End-points (ECLIPSE) study sponsored by GlaxoSmithKline. CT scans were used to determine the ratio of the size of the pulmonary artery to the aorta in current and former smokers with COPD, and the analysis revealed that an elevated ratio was a valid predictor of future exacerbation.
"The ability to predict which patients are likely to experience an exacerbation of their COPD symptoms requiring hospitalization is clinically significant," says J. Michael Wells, M.D., assistant professor in pulmonary medicine and lead author of the study. "Physicians armed with this knowledge may be able to employ a more aggressive treatment to this population in an attempt to reduce their risk of hospitalization."
Wells says the CT scan analysis appears to be a better predictor than other methods in use, which include measurements of lung function, quality of life, acid reflux and previous episodes of exacerbation.
Dransfield says CT scans — commonly done on patients with lung disease — are inexpensive and easy to read, potentially making the technique particularly useful for predicting exacerbations of COPD.
"This technique requires minimal training, is reproducible and can be obtained from routine CT images without the need for contrast or special software," Dransfield says. "Given the increased use of CT imaging in smokers, including the suggestion that COPD can be diagnosed with images alone, we suggest that the measurement of the ratio between the pulmonary artery and the aorta should be encouraged as a clinical tool."
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