DIFFERENCES IN AIRWAY WALL COMPLIANCE AS A POSSIBLE MECHANISM FOR WHEEZING DISORDERS IN INFANTS

High-frequency input impedance measurements (Z(f)) provide useful noni nvasive information on airway geometry and especially airway wall mech anics in the canine and human adult respiratory system. Using the high -speed interrupter technique (HIT), we have shown that it is possible to measure high-frequency Z(f) in infants up to 900 Hz, including anti resonant phenomena which are known to be related to wave propagation v elocity. This implies that the first antiresonant frequency (far,1) is a function of airway wall compliance. Since, airway wall mechanics ar e particularly important for the flow limitation phenomena, we wondere d whether we could find evidence that airway wall properties were impo rtant for the occurrence of how limitation during incremental methacho line challenge in infants, We measured Z(f) from 32-900 Nz and maximal how at functional residual capacity (V'maxFRC) by the rapid chest com pression technique in 10 infants (aged 36-81 weeks) with wheezing diso rders. far,1 increased significantly at very low doses of mch before a ny decline could be detected in V'maxFRC. We hypothesize that these ch anges in far,1 are determined by mch-induced decrease in airway wall c ompliance, High-speed interrupter technique in combination with rapid chest compression technique can be used to study developmental differe nces in airway function (particularly of airway wall properties) and t heir contribution to airway disease and response to bronchodilator the rapy in infants.