Relative Ability of Full and Partial Forced Expiratory Maneuvers to Identify Diminished Airway Function in Infants with Cystic Fibrosis

Abstract

The tidal and raised volume rapid thoracoabdominal compression techniques are increasingly used to detect diminished airway function in infancy. The aim of this study was to assess the relative ability of parameters measured by these techniques to identify diminished airway function in infants newly diagnosed with cystic fibrosis (CF) with and without clinical evidence of prior lower respiratory illness. A cross-sectional, prospective study design was used in which maximal flow at functional residual capacity (VmaxFRC) from the tidal technique and FVC, FEV0.5, FEF75, and FEF25-75 from the raised volume technique were measured in 47 infants with CF and 187 healthy infants of similar body size, sex distribution, ethnic group, and exposure to maternal smoking. Multiple linear regression was used to assess group differences and to calculate SD scores for each parameter for the infants with CF. Airway function was also compared with clinical assessments of respiratory status made by pediatric pulmonologists. FEV0.5 was significantly diminished in 13 infants with CF, of whom 4 had been identified by clinicians as having normal respiratory status. Only one infant with CF had a VmaxFRC below the estimated normal range. Airway function is diminished in infants with CF irrespective of prior lower respiratory illness and in those whose respiratory status is considered normal by pediatric pulmonologists. In infants with CF, the raised volume technique identified diminished airway function more frequently than the tidal technique.

Assessment of tidal breathing parameters in infants with cystic fibrosis

“…Lung function measurements were attempted in 47 infants with CF, details of whom have been published previously [15]. Infants with CF were diagnosed at a median (range) corrected age of 30 (6-93) weeks and tested within an interval from diagnosis of 12 (0-38) weeks.…”

“…Infants and young children newly diagnosed with CF by sweat test and/or by positive genotype for CF mutations [13] were recruited, as described in detail previously [14,15], from five specialist centres in London where neonatal screening is not routinely undertaken. Subjects were eligible if aged v24 months at diagnosis and free from additional congenital or acquired cardio-respiratory or neurological abnormalities.…”

Early detection of cystic fibrosis lung disease: multiple-breath washout versus raised volume tests

“…Power of study Previous work from this department has shown that differences in FEV 0.5 equating to at least 1 Z score (ie, 1 SD) are likely to be observed between groups of infants with and without cystic fibrosis 11 A sample size of 15 children per group would be sufficient to detect a difference equivalent to 1 SD in FVC, FEV 0.5 , FEF 75 and FEF between cystic fibrosis and control groups with 80% power at the 0.05 significance level.…”

“…9 Despite using slightly different equipment and software from that reported previously, the healthy infants had RVRTC results similar to those predicted 26 and to those we have reported previously. 11 Currently available data are insufficient to calculate accurate prediction equations or Z scores for LCI during infancy. Although it has been suggested that there may be a slight negative age dependency of LCI in healthy infants during the first months of life, 33 34 most of the infants in this study were over 6 months of age when these effects were less marked, and all but one of the healthy controls had results that fell within the normal range established for preschool children, ie ,7.8.…”

“…9 Forced flows and volumes obtained over an extended volume range (from near total lung capacity) have been shown to be more sensitive in detecting diminished airway function in infants with cystic fibrosis than the tidal rapid thoracic compression technique. [10][11][12] By contrast, several studies have shown that many younger children with cystic fibrosis have spirometry results that fall within the normal range, 4 13 14 and that indices of gas mixing derived from inert gas multiplebreath washout (MBW) may be more sensitive than spirometry in detecting early airway disease in both preschool and schoolage children with cystic fibrosis. 1 4 15 Reduced gas mixing efficiency or ''increased inhomogeneity in ventilation'' can result from differences in specific ventilation between lung units joined at branch points in the conducting airways.…”