Specific airway resistance, interrupter resistance, and respiratory impedance in healthy children aged 2–7 years

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Abstract
We report data on respiratory function in healthy children aged 2–7 years in whom we measured respiratory resistance by the interrupter technique (Rint); total respiratory impedance (Zrs), respiratory resistance (Rrs), and reactance (Xrs) by the impulse oscillation technique; and specific airway resistance (sRaw) by a modified procedure method in the whole body plethysmograph. Measurements were attempted in 151 children and were successfully obtained in 121 children with a mean (SD) age of 5.3 (1.5) years; no measurements were possible in 30 children (mean age 3 (0.9) years). The repeatability of measurements was independent of the age of the subjects, and the within‐subject coefficient of variation was 11.1%, 8.1%, 10.8%, and 10.2% for sRaw, Rint, Zrs, and Rrs at 5 Hz (Rrs5), respectively. All lung function indices were linearly related to age, height, and weight. A significant negative correlation with age, height, and weight was found for Rint, Zrs, and Rrs5. Xrs5 was positively correlated to age and body size. The mean values of Rint, Rrs5, Xrs5, and Zrs in children younger and older than 5 years were 1.04, 1.38, −0.5, and 1.48 kPa · L−1 · s and 0.9, 1.18, −0.37, and 1.23 kPa · L−1 · s, respectively. sRaw showed no significant correlation with body size or age and the mean sRaw in children younger and older than 5 years was 1.09 and 1.13 kPa · s, respectively. None of the indices of respiratory function differed between boys and girls. Xrs and Rrs exhibited a significant frequency dependence in the range of 5–35 Hz. The techniques applied in this study require minimal cooperation and allow measurement of lung function in 80% of our population of awake young children. Further studies are needed to evaluate the potentials of the presently established reference values for clinical and epidemiological purposes. Pediatr Pulmonol. 1998; 25:322–331.