Reference Values of interrupter respiratory resistance in healthy preschool white children

Background—Interrupter respiratory re-sistance (Rint) is reported to be useful in evaluating lung function in poorly collabo-rating patients. However, no reference values are available from large samples of preschool children using the standard interrupter method. The aim of this study was to define reference Rint values in a population of healthy preschool children. Methods—Rint was assessed without sup-porting the cheeks in children with no his-tory of wheeze from six kindergartens. To evaluate the eVects of upper airway com-pliance on Rint in healthy children, an additional group of preschool children with either no history of wheeze or no res-piratory symptoms at the time of testing underwent Rint measurements in our lung function laboratory with and without sup-porting the cheeks. Short term (about 1 minute apart) and long term (mean 2.5 months apart) repeatability of Rint meas-urements (2 SDs of the mean paired diVerence between measurements) was also assessed in children referred for cough or wheeze. Results—A total of 284 healthy white chil-dren (age range 3.0–6.4 years) were evalu-ated. Mean inspiratory and expiratory Rint (RintI and RintE) did not diVer significantly in boys and girls. Age, height, and weight showed a significant 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 significantly and independently cor-related with RintI, whereas only height was significantly and independently cor-related with RintE. Supporting the cheeks had no significant eVect on RintI (n=29, median 0.673 v 0.660 kPa/l.s, p=0.098) or RintE (n=39, median 0.702 v 0.713 kPa/l.s, p=0.126). Short term 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 children and have demonstrated the usefulness of this technique in assessing lung function in this age group. (Thorax 2001;56:691–695