Pediatric Reference Values for Respiratory Resistance Measured by Forced Oscillation

¹ From the Departments of Pediatrics and Epidemiology and Biostatistics, Montreal Children's Hospital, McGill University Faculty of Medicine, Montreal, Canada
² From the Department of Pediatrics, Montreal Children's Hospital, McGill University Faculty of Medicine, Montreal, Canada
³ From the Department of Probabilities and Statistics, University of Montpellier II, Montpellier, France

Objectives: To determine, in North American children, reference values for respiratory resistance measurements by the forced oscillation (Rfo) technique and to examine whether sitting height, as index of truncal length, is a better determinant of resistance, less influenced by race and gender, than standing height.

Design/setting: A prospective cross-sectional study of healthy nonobese children, carefully selected for absence of atopy, exposure to tobacco smoke, and recent upper respiratory tract infection.

Measurements: Three measurements of respiratory resistance by forced oscillation were obtained at the fixed frequencies of 8 Hz (Rfo₈), 12 Hz (Rfo₁₂), and at 16 Hz (Rfo₁₆) using the Custo Vit R (Custo Med GMBH; Munich, Germany). In cooperative children, routine spirometry (FEV₁ FVC, and peak expiratory flow rate [PEFR]) was also performed.

Results: We recruited 217 healthy children aged 3 to 17 years. Reproducible measurements of Rfo₈ were obtained for 206 children, Rfo₁₂ for 197 children, and Rfo₁₆ for 209 children. Normal FEV₁, FVC, and PEFR values were documented in all 69 subjects who were able to reproducibly cooperate with spirometry. Multiple linear regression identified measurements of either sitting or standing height as the best, and equally strong, determinants of respiratory resistance at all three frequencies. Gender and race were not important factors once either sitting or standing height measurement was considered. Our regression equations at 8 Hz are comparable to published reference values obtained at fixed frequencies of 6, 8, and 10 Hz using other instruments. However, in comparison to our results, prior values tended to underestimate resistance in the shortest children or to overestimate it in the tallest ones. Our regression equation for Rfo₁₂ is similar to the only previously published one, while no reference values at 16 Hz were available for comparison.

Conclusions: Height is the best predictor for total respiratory resistance at 8, 12, and 16 Hz in children aged 3 years. Use of sitting height does not appear to be a stronger determinant of resistance than standing height.

Key Words: child • forced oscillation technique • North America • oscillatory resistance • reference values • respiratory resistance • sitting height • spirometry • standing height

Submitted on July 24, 1997
Accepted on October 10, 1997

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