Double-tracer gas single breath washout - Variability and reproducibility compared with classical nitrogen washout tests

Background Inert tracer gas washout tests are noninvasive tools to assess ventilation inhomogeneity in small airway diseases. Multiple breath washouts (MBW) are time consuming, single breath washouts (SBW) require a difficult breathing maneuver. We want to assess feasibility, variability and reproducibilitiy of a new fast and easy double tracer gas single breath washout (DTG-SBW) 1 and compare this test with conventional nitrogen (N 2 ) washouts. Materials and methods In 40 healthy nonsmokers (n = 20 ≤ 40, n = 20 > 40 years) we performed a triplet of N 2 -SBW, N 2 -MBW and tidal DTG-SBW. Follow up was after 1 week and 1 month. We measured the lung clearance index LCI (N 2 -MBW), slope of phase III dN 2 (N 2 -SBW) and DTG-slope III (DTG-SBW) calculated with a new automated algorhythm. Results Mean (SD) LCI at baseline was 6.93 (0.61), mean (SD) dN 2 0.99 (0.42) %N 2 /L and mean (SD) DTG-slope III -0.207 (0.106) g/mol*L. LCI showed a statistically significant difference between younger and older subjects (mean LCI (SD) 6.62 (0.37) ≤ 40 years vs. 7.25 (0.64) > 40 years, p 2 and 22.6 % for DTG-Slope-III. The mean difference between tests was small for all three washouts – considering short term (1st vs. 2nd) as well as long term reproducibility (1st vs 3rd test). Conclusion Variability of the DTG-SBW is acceptable, reproducibility is good and comparable with standard nitrogen washout tests. The fast and easy DTG-SBW with new automated analysis may be applicable for diagnosis and assessment of small airway diseases. Reference 1 Singer F et al. PLoS ONE 2011; 6: e17588.