Respiratory input and transfer impedances in children 9-13 years old.

Reference values for respiratory impedances in children are scarce and limited to the situation where pressure is varied at the mouth. Total respiratory impedance was therefore measured from 4 to 30 Hz in 69 healthy children (9-13 yr) with both a pressure input at the mouth (input impedance, Zin) and a pressure input at the chest (transfer impedance, Ztr). Zin was characterized by the average resistance (R), the low-frequency limit of resistance (R0), the slope of the resistance-frequency curve (S), respiratory elastance (E) and respiratory inertance (I). Similar coefficients (R0', S', E', I'), some of which however have slightly different physiological meanings, were derived from Ztr. R, R0 and R0' were found to be significantly correlated to body height (p less than 0.001) and, independently, to age (p less than 0.05): R (kPa X l-1 X s) = 1.76-5.29 10(-3) height (cm) -4.13 10(-2) age (yr). Elastances were better correlated to height than to age: E (kPa X l-1) = 20.95-0.101 height (cm) and inertances better correlated to age than to height: I (Pa X l-1 X s2) = 4.39-0.128 age (yr). S and S' were not correlated to biometric variables. No difference was found between children living in polluted (n = 36) and nonpolluted (n = 33) areas, except for S which was significantly lower in the first group (p less than 0.01).