Background and Objective: Preschool children can perform quality, reproducible spirometric maneuvers, provided appropriate equipment is used and specially trained nursing staff training are available. However, use of spirometry for the diagnosis and follow-up of preschool children with respiratory diseases remains limited in clinical practice, because consensus on test quality and acceptability criteria and reference data are lacking. We initiated the present study with the aim of developing reference equations, since tables of normal values for this age group are not available in our area.

Patients and Methods: The study population comprised healthy preschool children in our community. Normal values for exhaled nitric oxide in this age range were assessed. Regression equations were constructed using univariate and multivariate models.

Results: A total of 114 healthy preschool children aged 3 to 6 years were enrolled. According to the criteria of the American Thoracic Society/European Respiratory Society, 60 children were able to perform acceptable and reproducible spirometric maneuvers. The best correlations were observed for the untransformed linear regression model that included height. The correlation coefficients for forced vital capacity (FVC), forced expiratory volume in the first second (FEV₁), and FEV_0.5 were 0.89, 0.88, and 0.86, respectively. The regression equations for the calculation of reference values were as follows:
FVC = –2.6 + 0.036 x height, cm
FEV₁ = –2.04 + 0.029 x height, cm
FEV_0.5 = –1.53 + 0.022 x height, cm
We obtained fraction of inhaled nitric oxygen (FeNO) values for 56 children. The mean (SD) value was 11 (4.9) ppb.

Conclusions: Most preschool children in our area were able to perform quality spirometry maneuvers. We obtained regression equations that allowed us to calculate the reference ranges in our population and the distribution of normal FeNO values.

Key words: Spirometry. Preschool children. Reference values. Exhaled nitric oxide.