Lung function measurements in children - copsac
Lung function measurements in children - copsac
Lung function measurements in children - copsac
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After correct<strong>in</strong>g the factory sett<strong>in</strong>gs at the deviat<strong>in</strong>g center there were no longer<br />
differences between the centers and normative values were generated <strong>in</strong> this multicenter<br />
sett<strong>in</strong>g. The problem was not discovered by the standard calibration of flow, box<br />
leak and <strong>in</strong>ternal box pressure. Current calibration only assesses flow measured by the<br />
pneumotachograph, leak from the box and pressure transducer. Previous studies have<br />
shown that the electronic BTPS compensation may <strong>in</strong>fluence the accuracy of sRaw<br />
<strong>measurements</strong> (15, 55). Klug et al. found when us<strong>in</strong>g electronic BTPS compensation the<br />
sRaw <strong>measurements</strong> were systematically overestimated by 43% with <strong>in</strong>creas<strong>in</strong>g<br />
respiratory rate compared with true BTPS conditions (15). The electronic compensation<br />
(BTPS) was done identically by the different software versions. The available<br />
calibration does not assess the f<strong>in</strong>al resistance measure, which is generated by<br />
algorithms buried <strong>in</strong> the software with sett<strong>in</strong>gs often <strong>in</strong>accessible to the end-user.<br />
Thereby errors <strong>in</strong> software or mechanics may go unnoticed with potential impact on<br />
cl<strong>in</strong>ical evaluation and flawed accuracy as illustrated <strong>in</strong> our study. It is the key-message<br />
of our study that center-effects were seen and could only be expla<strong>in</strong>ed by difference <strong>in</strong><br />
the software hidden from the end-user.<br />
We chose not to repeat the study with the same procedure after the correction; first of all<br />
because the travell<strong>in</strong>g was time consum<strong>in</strong>g and second the observers and <strong>children</strong><br />
would be biased by the prior knowledge.<br />
We could have used adults as biological controls, but they could be biased even if we<br />
bl<strong>in</strong>ded the results from each center and we would have to change the observers.<br />
The local observers had different experience level <strong>in</strong> sRaw <strong>measurements</strong>. Two local<br />
observers had only measured approximately 5-10 <strong>children</strong> before perform<strong>in</strong>g the study<br />
and some had 5-10 years of experience.<br />
The <strong>children</strong> had good repeatability and were cooperative. The mean sRaw for the<br />
biological controls was with<strong>in</strong> but a little lower than the normative data (Figure 4+5) if<br />
we do not consider center no. 1. We consider the <strong>children</strong> physiologically representative<br />
for preschool <strong>children</strong> and the lower mean sRaw could be due to the low number of<br />
<strong>children</strong>.<br />
A mechanical <strong>in</strong>fant lung model analogue has previously been developed for quality<br />
control of <strong>in</strong>fant whole-body plethysmographs (52) but a model test<strong>in</strong>g for preschool<br />
<strong>children</strong> is not available to the end-user. This study suggests the need for development<br />
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