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Lung Diffusing Capacity for Nitric Oxide and Carbon Monoxide^*

Dependence on Breath-Hold Time

^* From the Institute and Outpatient Clinic for Occupational, Social and Environmental Medicine (Dr. Dressel, Ms. Filser, Ms. de la Motte, Dr. Nowak, and Dr. Jörres), Ludwig-Maximilians-University, Munich; Department of Pneumology (Dr. Fischer and Dr. Huber), Medizinische Klinik Innenstadt, Ludwig-Maximilians-University, Munich; and Viasys Healthcare GmbH (Mr. Steinhaeusser), Würzburg, Germany.

Correspondence to: Holger Dressel, MD, MPH, Institute and Outpatient Clinic for Occupational, Social and Environmental Medicine, Ludwig-Maximilians-University Munich, Ziemssenstrasse 1, D-80336 München, Germany; e-mail: holger.dressel{at}med.uni-muenchen.de

Abstract

Background: The combined measurement of diffusing capacity of the lung for nitric oxide (DLNO) and diffusing capacity of the lung for carbon monoxide (DLCO) is a simple, noninvasive tool, but methodologic factors might influence results and reproducibility. We thus quantified the influence of breath-hold time on DLCO and DLNO in subjects with or without airway disease.

Methods: Simultaneous single-breath measurements of DLCO and DLNO were performed in 10 patients with cystic fibrosis (CF) [mean ± SD age, 33 ± 9 years; FEV₁, 69 ± 28% of predicted] and 10 healthy subjects (age, 31 ± 9 years; FEV₁, 108 ± 8% of predicted), using the Masterscreen PFT (Viasys/Jaeger; Höchberg, Germany), with 45 ppm of inspired nitric oxide (NO), and breath-hold times of 4 s, 6 s, 8 s, and 10 s. The last two of three consecutive measurements were used for analysis.

Results: In healthy subjects but not patients with CF, DLNO, and DLCO differed significantly (p < 0.05 each) between breath-hold times. Differences primarily occurred at 4 s and 10 s, while at 6 s and 8 s alveolar volume (VA), DLNO, DLCO, and DLNO/DLCO were similar. Variability of consecutive measurements (either three or the last two measurements) did not depend on breath-hold time. At 8 s, mean variabilities of DLNO and DLCO in healthy subjects were 4.9% and 2.5%, respectively, and 4.2% and 3.2% at 6 s. At 8 s, mean variabilities of DLNO and DLCO in CF patients were 4.4% and 1.9%, and 7.4% and 3.3% at 6 s.

Conclusions: Single-breath determinations of DLNO and DLCO showed no difference between breath-hold times of 6 s and 8 s in subjects with or without airway obstruction, and reproducibility was acceptable. Standardization of breath-hold time for DLNO measurements seems important for clinical and research comparisons.

Key Words: airway obstruction • carbon monoxide • cystic fibrosis • lung diffusing capacity • nitric oxide • variability