Forced expiratory flows and volumes in a Swedish cohort of healthy term infants

Background The use of pulmonary function tests (PFTs) in infants has increased during the last decades, making the need for equipment- and ethnic-specific reference data mandatory for appropriate interpretation of the results. Aim Our aim was to investigate how well the already published reference equations for infant spirometry fit a healthy population of Swedish infants. Method We performed forced tidal and raised volume expiratory maneuvers in healthy infants using Jaeger BabyBody equipment. Results PFT data were collected from 91 healthy infants aged between 3 months to 2 years at 143 occasions. Mean (standard deviation) z-scores were 0.68(1.33) for maximal flow at functional residual capacity (V'maxFRC), -0.15(0.96) for forced vital capacity (FVC), 0.40(1.33) for the forced expired volume in the initial 0.5 seconds (FEV0.5) and 0.52(0.93) for the ratio FEV0.5/FVC, respectively. Z-scores for all indices but FEV0.5/FVC were highly dependent on length. Conclusions We have shown that the use of previously published reference equations may result in an age-related misinterpretation of lung function measure in a Swedish infant population.