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Single-Breath Diffusing Capacity of the Lung for Carbon Monoxide^*

A Predictor of PaO₂, Maximum Work Rate, and Walking Distance in Patients With Emphysema

^* From the Cedars-Sinai Medical Center (Dr. Mohsenifar), Los Angeles, CA; the Bloomberg School of Public Health (Mr. Lee) and the School of Medicine (Dr. Wise), the Johns Hopkins University, Baltimore, MD; the Temple University School of Medicine (Dr. Criner), Philadelphia, PA; Columbia University (Dr. Ginsburg), New York, NY; the University of Pittsburgh School of Medicine (Dr. Sciurba), Pittsburgh, PA; and the Ohio State University (Dr. Diaz), Columbus, OH.

Correspondence to: Zab Mohsenifar, MD, FCCP, Cedars-Sinai Medical Center, Division of Pulmonary/Critical Care Medicine, 8700 Beverly Blvd, Room 6732, Los Angeles, CA 90049; e-mail: mohsenifarz{at}cshs.org

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.

Key Words: diffusing capacity • emphysema • exercise tests • gas exchange • lung disease • PaO₂

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				E. M. Snyder, B. D. Johnson, and K. C. Beck An open-circuit method for determining lung diffusing capacity during exercise: comparison to rebreathe J Appl Physiol, November 1, 2005; 99(5): 1985 - 1991. [Abstract] [Full Text] [PDF]