Objective: The National Emphysema Treatment Trial (NETT) is a randomized, multicenter, clinical trial comparing two different methods of lung volume reduction surgery plus medical therapy to medical treatment alone in patients with advanced emphysema. The purpose of this article was to use the data obtained from the NETT to assess the ability of the single-breath diffusing capacity of the lung for carbon monoxide (Dlco) to predict the need for supplemental oxygen during rest and exercise, as well as overall exercise capacity.
Methods: One thousand seventy-one patients with a mean (± SD) FEV1 of 0.76 ± 0.24 L were studied.
Results: The mean Dlco was 8.0 ± 3.1 mL/min/mm Hg (28 ± 10% of predicted). The mean resting Pao2 was 64 ± 10 mm Hg. There was a positive association between Dlco and both resting Pao2 and the requirement for oxygen during a walk at 1 mile per hour (mph). The odds of requiring supplemental oxygen while walking at 1 mph was nine times greater in patients with a Dlco of ≤ 20% of predicted than for patients with a Dlco of > 35% of predicted, after adjusting for age and gender. Eighty four percent of individuals with a Dlco of ≤ 20% required supplemental oxygen with low levels of exercise compared to 38% of those with a Dlco of > 35%.
Conclusion: Our results demonstrated that patients with reduced Dlco, particularly when ≤ 20% of predicted, are more likely to have reduced Pao2 at rest and are more likely to require supplemental oxygen with low levels of activity. Thus, Dlco is useful in evaluating whether supplemental oxygen is required for exercise.