Lung diffusing capacity for nitric oxide and carbon monoxide

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; Hochberg, 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.