Reference values of interrupter respiratory resistance in healthy preschool white children

Background-Interrupter respiratory resistance (Rint) is reported to be usef ul in evaluating lung function in poorly collaborating patients. However, n o reference values are available from large samples of preschool children u sing the standard interrupter method. The aim of this study was to define r eference Rint values in a population of healthy preschool children. Methods-Rint was assessed without supporting the cheeks in children with no history of wheeze from six kindergartens. To evaluate the effects of upper airway compliance on Rint in healthy children, an additional group of pres chool children with either no history of wheeze or no respiratory symptoms at the time of testing underwent Rint measurements in our lung function lab oratory with and without supporting the cheeks. Short term (about 1 minute apart) and long term (mean 2.5 months apart) repeatability of Rint measurem ents (2 SDs of the mean paired difference between measurements) was also as sessed in children referred for cough or wheeze. Results-A total of 284 healthy white children (age range 3.0-6.4 years) wer e evaluated. Mean inspiratory and expiratory Rint (RintI and RintE) did not differ significantly in boys and girls. Age, height, and weight showed a s ignificant inverse correlation with both Rinti and RintE in the univariate analysis with linear regression. Multiple regression with age, height, and weight as the independent variables showed that all three variables were si gnificantly and independently correlated with Rinti, whereas only height wa s significantly and independently correlated with RintE. Supporting the che eks had no significant effect on RintI (n=29, median 0.673 nu 0.660 kPa/l.s , p=0.098) or RintE (n=39, median 0.702 nu 0.713 kPa/l.s, p=0.126). Short t erm repeatability was 0.202 kPa/l.s for RintI (n=50) and 0.242 kPa/l.s for RintE, (n=69). Long term repeatability was 0.208 kPa/l.s for RintE (n=26). Conclusions-We have reported reference Rint values in preschool white child ren and have demonstrated the usefulness of this technique in assessing lun g function in this age group.