Normative Data and Predictive Equation of Interrupter Airway Resistance in Preschool Children in Japan

Measurement of interrupter airway resistance (Rint) is a convenient alternative to standard spirometry for assessing respiratory function in uncooperative young children. The aim of the present prospective study was to establish the normative data and predictive equation of Rint in Japanese preschool children. A total of 214 children were enrolled from a single kindergarten; however, 129 were excluded because they met at least 1 of the exclusion criteria, such as wheezing history or recent common cold. Expiratory Rint values were assessed in 85 of the children, but technically unsatisfactory measurements were obtained in 5 of them. Thus, 80 healthy Japanese children (39 boys and 41 girls) without any history or symptoms of respiratory tract diseases were evaluated. Their age, body height, and body weight ranges (median) were 1.67 to 6.42 (4.38) years, 79.8 to 120.9 (102.5) cm, and 10.4 to 24.9 (15.8) kg, respectively. The mean Rint was 0.93±0.25 kPa/L/s (range=0.46-1.49 kPa/L/s). The Rint tended to decrease with increasing age and body height (r=-0.65; P<0.01), but sex played no significant role (P=0.71). The predictive equation based on body height derived by linear regression was expiratory Rint (kPa/L/s) =2.513-0.01567×body height (cm) (multiple correlation coefficient=0.653). Because 79 of the 80 measured Rint values were within 140% of the predictive Rint value, we calculated a 140% cut-off for predicting bronchoconstriction. Our results provide a reference value for evaluating the degree of airway obstruction in young Japanese children.