Lung function measurements in children - copsac

age 2 years (mean age 11.4 months) in the COPSAC cohort. They could have had RSV
bronchiolitis after drop-out of the cohort study without our knowledge. We decided to
include them in the control group because in general drop-outs are most likely children
who stay healthy, and the families had an option to become active in the cohort again at
anytime.
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 this study.
Confounder adjustment included mothers smoking during 3 rd trimester and gender both
well known risk factors for bronchiolitis (57, 141, 142, 188-192). 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 (135). We did not confounder adjust for other risk factors such as month of birth,
socio-economic status, or siblings.
We found an overweight of boys (73%) in the RSV group in agreement with previous
reports (140, 141, 188, 189, 193).
Meaning of the study
Acute RSV bronchiolitis may occur in otherwise healthy infants. It is not known
whether viral bronchiolitis is causatively related to asthma or simply identifies infants at
risk for subsequent wheezing from an atopic predisposition or pre-existing abnormal
lung function (194, 195). Infants with impaired pulmonary function at one month of age
was reported to be prone to recurrent wheezy episodes and asthma (58, 100-103, 105,
108, 196). Therefore it has been assumed that acute bronchiolitis or wheeze develop due
to pre-morbid abnormal pulmonary lung function consistent with smaller airway size
(103, 104, 106, 110, 111). But these are indirect evidence as clinical wheezing illness
was used as end-point.
Our study showed no association between early lung function (FEV 0.5 and bronchial
hyperresponsiveness) and subsequent RSV bronchiolitis. There were no difference in
pre-morbid lung function and bronchial hyperresponsiveness in infants who later
develop RSV bronchiolitis and those without such severe infection. This could mean
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