Lung function measurements in children - copsac

prospectively if baseline lung function is lower in infant developing RSV-bronchiolitis. On the other
hand comparing bronchial responsiveness showed a narrow confidence interval (-26% to +20%);
i.e. suggesting it seems unlikely that bronchial hyperresponsiveness was the distinguishing factor in
infants later developing RSV-bronchiolitis.
The strengths of this study were the unique prospective nature of the birth cohort study with lung
function assessments before the development of bronchiolitis together with the close clinical follow-up
to the research clinic and daily symptom recordings assuring ascertainment of all severe
episodes.
Lung function measurements were completed in a large group of asymptomatic infants (404) within
a narrow age-range around 1 month after birth. This is the largest study of lung function in neonates
under standardized conditions. Baseline lung function was conducted by infant spirometry adapted
as the state-of-the-art Raised Volume Rapid Thoracic Compression technique which provides flowvolume
measures. The previous analyses found PtcO 2 was the most sensitive parameter for 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 (25, 27).
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.
Nineteen of the 22 infants (86%) with RSV bronchiolitis were hospitalized. Danish children are
generally only admitted if they need support with feeding tube, suction of upper airways, mask inhalations
or nasal continuous positive airway pressure, which ensures a certain severity in their
RSV infection in our study.
Confounder adjustment included mothers smoking during 3 rd trimester and gender both well known
risk factors for bronchiolitis (41-47). We found an overweight of boys (73%) in the RSV group in
agreement with previous reports (41-43, 48, 49). Lung function measurement data were calibrated
for birth length and lifespan at examination date because these parameters have shown to affect
early lung function in the COPSAC cohort (29).
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