Lung function measurements in children - copsac

After correcting the factory settings at the deviating center there were no longer
differences between the centers and normative values were generated in this multicenter
setting. The problem was not discovered by the standard calibration of flow, box
leak and internal box pressure. Current calibration only assesses flow measured by the
pneumotachograph, leak from the box and pressure transducer. Previous studies have
shown that the electronic BTPS compensation may influence the accuracy of sRaw
measurements (15, 55). Klug et al. found when using electronic BTPS compensation the
sRaw measurements were systematically overestimated by 43% with increasing
respiratory rate compared with true BTPS conditions (15). The electronic compensation
(BTPS) was done identically by the different software versions. The available
calibration does not assess the final resistance measure, which is generated by
algorithms buried in the software with settings often inaccessible to the end-user.
Thereby errors in software or mechanics may go unnoticed with potential impact on
clinical evaluation and flawed accuracy as illustrated in our study. It is the key-message
of our study that center-effects were seen and could only be explained by difference in
the software hidden from the end-user.
We chose not to repeat the study with the same procedure after the correction; first of all
because the travelling was time consuming and second the observers and children
would be biased by the prior knowledge.
We could have used adults as biological controls, but they could be biased even if we
blinded the results from each center and we would have to change the observers.
The local observers had different experience level in sRaw measurements. Two local
observers had only measured approximately 5-10 children before performing the study
and some had 5-10 years of experience.
The children had good repeatability and were cooperative. The mean sRaw for the
biological controls was within but a little lower than the normative data (Figure 4+5) if
we do not consider center no. 1. We consider the children physiologically representative
for preschool children and the lower mean sRaw could be due to the low number of
children.
A mechanical infant lung model analogue has previously been developed for quality
control of infant whole-body plethysmographs (52) but a model testing for preschool
children is not available to the end-user. This study suggests the need for development
22