Results: A total of 1419 patients with severe COPD were included in the analysis mean age 66.4 years (standard deviation 6.3), 38% females, and 422 (29.7%) had baseline hypercapnia. Stepwise variable selection yielded 10 statistically significant associations in multivariate regression. An inclusive list of 32 potential predictor variables were selected a priori based on consensus of the investigators and literature review. All patients with complete baseline data for the key predictor variables were included. Methods: This is a secondary analysis of the clinical, physiologic and imaging data from the National Emphysema Treatment Trial (NETT). However, these factors have not previously been systematically analyzed in a large, well-characterized population of severe COPD patients. Multiple factors in COPD are thought to contribute to the development of hypercapnia including increased carbon dioxide (CO 2) production, increased dead space ventilation, and the complex interactions of deranged respiratory system mechanics, inspiratory muscle overload and the ventilatory control center in the brainstem. Rationale: Hypercapnia develops in one third of patients with advanced chronic obstructive pulmonary disease (COPD) and is associated with increased morbidity and mortality.
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