Lung function measurements in children - copsac

detection changes in lung function (dose-response curve metacholine challenge),
followed by FEV 0.5 , both superior to other indexes of forced spirometry as well as all
tidal breathing indexes (10, 133); therefore we only report these two parameters in this
study. A shorter time limit as 0.4 s may have improved the sensitivity (185). Values of
FEF% have been reported to be more discriminative than FEV(t) in some studies (186).
The discrepant finding could be due to the different definition of sensitivity. In our
previous study the sensitivity was defined as the ability to detect induced changes in
lung function within an individual while in other studies it was defined as the ability to
discriminate between disease and healthy infants. An Australian study showed that
FEV(t) were more reproducible than flow measurements in the tidal volume range and
also found that FEV(t) were significantly lower in wheezy infants with less overlap than
flow measurements (187).
The coefficient of variation for PtcO 2 and FEV 0.5 were 4% and 7% respectively based
on measurements before and after saline solution inhalation. RVRTC-measurements
were automatically registered, and results from PtcO 2 were read from the print-outs by
an independent person, different from the operators. Volume-time curves were only
accepted if the forced expiration proceeded smoothly, with no signs of glottic closure or
early inspiration. The software defined FVC as the first plateau on the volume-time
curve, and only measurements with FVC appearing after 0.5 seconds, and with FEV 0.5
being smaller than or equal to FVC were accepted. In addition, FVC was only accepted
if correctly defined as the plateau appearing after a full expiration. The curve containing
the median value for the FEV 0.5 was used for the analyses of both volume and flow
parameters (133). The choice of “best” trial differs in this study from the ATS/ERS
guidelines which recommend choosing the “best” (technically) trial defined as the one
with either the highest sum of FVC and FEV 0.4/0.5 or FEF 25-75 , provided they are within
10% of the next best loop (2).
We analyzed bronchial responsiveness as a quantitative trait in the RSV and control
group rather than dichotomizing the infants into +/- hyperresponsiveness.
All cases of non-RSV bronchiolitis and acute severe wheeze episodes were excluded
from the control group, which would tend to favor a difference between our cases and
controls. We made a spot check in the control group and found no acute wheeze
episodes in their hospital records. 44 children in the control group dropped out before
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