Lung function measurements in children - copsac

Introduction
Respiratory syncytial virus (RSV) is a common cause of lower respiratory tract disease in infants
(1-4). Two-three percent of infants react to RSV infection with bronchiolitis before age 1(5-7). Infants
with impaired pulmonary function seem more prone to recurrent wheezing episodes (8-16).
Therefore it has been speculated that pre-existing abnormal airway resistance and/or bronchial hyper-responsiveness
could account for the development of bronchiolitis in response to RSV infection
(17-19).
“Copenhagen Prospective Study on Asthma in Childhood” (COPSAC) is a prospective clinical
study of a birth-cohort, which included measurements of baseline lung function and bronchial responsiveness
to methacholine at 1 month by infant spirometry (20). The close clinical follow-up allowed
prospective identification of infants who developed RSV bronchiolitis.
This report aims to compare the preexisting baseline lung function and bronchial responsiveness in
infants who later developed RSV bronchiolitis with those who did not develop bronchiolitis.
Materials and methods
411 infants born at term (203 boys) of mothers with physician-diagnosed asthma were enrolled at
the age of 1 month in the prospective birth cohort study Copenhagen Prospective Studies on Asthma
in Childhood (COPSAC) (21-23). Both parents gave written informed consent. The study was
approved by the Local Ethics Committee ((KF)01-227/97), and the Danish Data Protection Agency
(2008-41-1754).
Lung function measurement in neonates
Lung function was assessed during sedation by infant spirometry at 1 month applying the raised
volume rapid thoracic compression technique (RVRTC). The method was performed in agreement
with ATS/ERS standards (24). An inflatable “squeeze”-jacket was wrapped around the infant's
chest and abdomen. A subsequent inflation of the jacket provided the passive expiration and flow
was measured using a pneumotachograph with an aircushion facemask (20, 25, 26).
Baseline flow was measured as the Forced Expiratory Volume at the first 0.5 second (FEV 0.5 ) (20,
25).
Bronchial responsiveness to methacholine was assessed by FEV 0.5 as well as continuous measurements
of trans-cutaneuos oxygen (PTcO 2 ) (TCM3; Radiometer; Copenhagen, Denmark). The methacholine
was administered in quadrupling dose-steps by a dosimeter attached to a nebulizer (SPI-
3