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'_max FRC), -0.15(0.96) for forced vital capacity (FVC), 0.40(1.33) for the forced expired volume in the initial 0.5 seconds (FEV_0.5 ) and 0.52(0.93) for the ratio FEV_0.5 /FVC, respectively. Z-scores for all indices but FEV_0.5 /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.