Abstract
Multiple breath washout outcomes in infants are setup-dependent
Introduction: Multiple breath washout (MBW) is a sensitive test to measure lung function from infancy on. The currently used infant setup requires partly user-dependent signal processing, which may reduce robustness. Recently improved hard- and software may overcome previous limitations.
Aim: We did a validation study and assessed (i) feasibility and (ii) compared functional residual capacity (FRC) values and variability of both setups in-vitro and in-vivo.
Methods: We performed MBW in a Plexiglas lung simulator using infant-corresponding lung volumes and breathing patterns under simulated body temperature and humidity, as well as in four healthy and four infants with cystic fibrosis, with the new (Exhalyzer D, Spiroware 3.2.0, Ecomedics) and the old setup (Exhalyzer D, Ecomedics / WBreath 3.18.0, ndd) in random sequence.
Results: FRC generated in the lung simulator showed better agreement with the FRC measured with the new setup [36 runs, mean(SD) difference -1.5(2.2)%] compared to the old setup [36 runs, 6.3(10.5)%, p<0.001]. The in-vivo feasibility of MBW of both setups was 100%. We found a low intra-subject variability in FRC per setup, but a significant offset in FRC between setups (mean FRC difference 39.7%, range 18.9;65.7, p=0.008). Simple user-defined corrections in both setups decreased FRC differences (mean 14.0%, range -6.4; 42.3, p=0.08). Those results were confirmed in-vitro.
Conclusion: The new setup is applicable in infants and measures FRC reliably in-vitro. However, FRC values are not interchangeable. Small user-defined changes in software settings influence MBW outcomes. Further validation work is needed before the new setup can be widely used.