Fractionating respiratory resistance in young children.

Total respiratory resistance (Rrs) and the fraction of this resistance located peripherally, (Fp) were measured in a group of children (3--5 yr old). The technique used forced random noise to characterize the frequency dependence of effective resistance and an algorithm to compute Rrs and Fp from these data. The overall mean value +/- SD for Fp was 0.534 +/- 0.070; the mean value of 0.464 for the six children near 5 yr of age was significantly different (P less than 0.001) from the mean value of 0.576 found in the younger children. The overall mean value +/- SD for Rrs was 16.9 +/- 5.8 cmH2O.l-1.s; individual values appeared to be correlated with height. These results agree with previous reports indicating that children have a larger fraction of respiratory resistance in the periphery than do adults.