BACKGROUND: The earliest change associated with airflow obstruction in small airways is reflected in a concave shape on the maximum expiratory flow-volume loop (MEFVL). The shape of the MEFL changes with age but reference values for curvilinearity indices (CI) for preschool children have not been published. We aimed to describe the normal curvilinearity of healthy preschool MEFVL by CI (the β angle and the ratio of maximum expiratory flow when 50% of forced vital capacity remains to be expired/peak expiratory flow (MEF(50%) /PEF)) and to test their capacity in detecting concavity in preschool children with wheezing disorders. METHODS: Spirometric data were obtained from 132 healthy preschool children and 171 3-to-5-year-old preschool children with wheezing disorders and reference values for CI calculated. RESULTS: Mean (SD) β angle of healthy children was 203° (16°) and mean MEF(50%) /PEF of healthy children was 0.71 (0.12) indicating convexity of MEFVL, both decreased with increasing age (P = 10(-4) ). Children with wheezing disorders had lower z-score values of CI (P ≤ 10(-6) ) indicating more concave MEFVL. Among the two CI, MEF(50%) /PEF allowed for the best discrimination between healthy children and children with wheezing disorders (Wilks' lambda = 0.898, P = 10(-7) ). CONCLUSION: These CI can detect and quantify the concavity of the descending limb of the MEFVL in preschool children with wheezing disorders, MEF(50%) /PEF having the highest sensitivity in detecting the concavity.
BACKGROUND: The earliest change associated with airflow obstruction in small airways is reflected in a concave shape on the maximum expiratory flow-volume loop (MEFVL). The shape of the MEFL changes with age but reference values for curvilinearity indices (CI) for preschool children have not been published. We aimed to describe the normal curvilinearity of healthy preschool MEFVL by CI (the β angle and the ratio of maximum expiratory flow when 50% of forced vital capacity remains to be expired/peak expiratory flow (MEF(50%) /PEF)) and to test their capacity in detecting concavity in preschool children with wheezing disorders. METHODS: Spirometric data were obtained from 132 healthy preschool children and 171 3-to-5-year-old preschool children with wheezing disorders and reference values for CI calculated. RESULTS: Mean (SD) β angle of healthy children was 203° (16°) and mean MEF(50%) /PEF of healthy children was 0.71 (0.12) indicating convexity of MEFVL, both decreased with increasing age (P = 10(-4) ). Children with wheezing disorders had lower z-score values of CI (P ≤ 10(-6) ) indicating more concave MEFVL. Among the two CI, MEF(50%) /PEF allowed for the best discrimination between healthy children and children with wheezing disorders (Wilks' lambda = 0.898, P = 10(-7) ). CONCLUSION: These CI can detect and quantify the concavity of the descending limb of the MEFVL in preschool children with wheezing disorders, MEF(50%) /PEF having the highest sensitivity in detecting the concavity.