[Single-breath and rebreathing methods for measurement of pulmonary diffusing function: a comparative study].

Objective To compare the difference of pulmonary diffusing capacity measured by single-breath (SB) and re-breathing (RB) in normal subjects, patients with interstitial lung disease (ILD) and chronic obstructive pulmonary disease (COPD). Methods We enrolled a cohort of subjects from the Guangzhou Institute of Respiratory Disease between September 2011 and February 2012: control group 29 (male 9, female 20, 42-74 y), ILD group 32 (male 15, female 17, 41-72 y), COPD group 32 (male 28, female 4, 40-75 y). All subjects underwent pulmonary diffusing capacity test using SB or RB method according to random figures order list. Diffusing capacity of carbon monoxide per predicted measured by SB method (SB-DLCO%pred) of the normal group was used as the standard to adjust the diffusing capacity of carbon monoxide per predicted measured by RB method (RB-DLCO%pred) and diffusing capacity of carbon monoxide per liter of VA per predicted measured by RB (RB-DLCO/VA%pred) in the 3 groups, respectively. Comparisons between 2 groups were performed by using the independent-sample t test, among more than 2 groups by using the One-Way ANOVA test, while the ROC curve was used to calculate the area under curve (AUC) and its 95%CI. Results In the control group, 15 subjects' RB-DLCO%pred was lower than 80%, and the mean value (78.8±2.1)% was also lower than 80%. Using SB-DLCO%pred of the normal group as a standard to adjust the RB-DLCO%pred, the corrected value was 1.097, and then this value was used to adjust RB-DLCO/VA%pred in the 3 groups, respectively. Before correction DLCO%pred [the control group: (91.2±1.9)% vs (78.8±2.1)%; the ILD group: (45.8±2.6)% vs (60.0±1.9)%; the COPD group: (66.3±2.9)% vs (56.6±1.6)%]and DLCO/VA%pred [the control group: (99.8±2.3)% vs (84.6±4.5)%; the ILD group: (75.9±3.0)% vs (88.5±5.4)%; the COPD group: (80.2±3.7)% vs (50.6±2.5)% ] between the SB and RB were statistically different among the 3 groups. After correction, only the DLCO%pred [(45.8±2.6)% vs (65.8±2.1)%], DLCO/VA%pred [ (75.9±3.0)% vs (102.2±6.2)%] of the ILD group and the DLCO/VA%pred [(80.2±3.7) vs (58.3±2.8)%] of the COPD group had significant difference between the 2 methods(t=-6.00-4.68, all P<0.01). The test time of re-breathing in the COPD group (106±5) s was significant longer than that of the ILD group (73±4) s and the control group (79±5) s (F=11.99, P<0.01), and the correlation between DLCO/VA%pred and the test time(r=-0.661, P<0.01) was higher than the relationship between DLCO%pred and the test time (r=-0.391, P<0.01). Furthermore, in the ILD group, the area of RB-DLCO%pred under ROC was 0.893, 95%CI being 0.817-0.970. In the COPD group, the area of RB-DLCO/VA%pred under ROC was 0.895, 95%CI being 0.811-0.979. Conclusions There were differences between re-breathing and single-breath in measuring diffusing capacity. The present predicted value of the re-breathing method needed further study to confirm its applicability. Re-breathing method was more consistent with the respiratory physiology, and might be a better method to detect diseased states. Key words: Pulmonary disease, chronic obstructive; Lung diseases, interstitial; Pulmonary diffusing capacity