4.2.1 Clinical impact of measurement error
The initial concerns that the findings of Wyler et al.1 about the measurement error in the widely used MBW
software Spiroware 3.2.1 could tremendously change utility of LCI in
clinical routine, can be rejected by our findings. We could show, that
clinimetric properties of LCI still hold, even though with a slightly
smaller magnitude based on overall lower LCI values. This is due to the
measurement principle of the test, the indirect
N2-calculation was found to be overestimated by the
cross-sensitivity error in the O2 and
CO2- signals, leading to a prolongation of the washout
with falsely high LCI values. Our results suggest that clinical
interpretation of LCI change is not affected by the correction of this
error. As such we can support recently published results from clinical
trials and extent the interpretation into the clinical application2.
4.2.2 Impact on feasibility (success rates of
measurements)
Since the correction of the gas measurement error results in shorter
washouts, we were able to reanalyze all our trials with the corrected
software version 22. Thus, also in clinical practice,
overall N2-MBW will become shorter with the corrected
software which might increase the feasibility of the test, especially in
the younger and possibly less cooperative age range but also in patients
with more advanced disease and longer washout times13,22.
4.2.3 Impact on Repeatability
Overall, we found short-and midterm repeatability17,18 to be similar after cross-sensitivity
correction, and thus limits for intervisit changes and variability to be
unaffected. Within-subject between test standard deviation remained
independent of the magnitude of LCI, which preserves the property of LCI
to guide individual clinical decisions.