Airway and respiratory tissue mechanics in normal infants

Low-frequency respiratory impedance (Zrs) was measured by applying a forcin g signal, between 0.5 and 21 Hz at a transrespiratory pressure of 20 cm H2O , in a cross-sectional study of 37 normal infants. A model containing an ai rway resistance (Raw) and inertance (law) and a tissue damping (G) and elas tance (H) was fitted to the individual Zrs. Forced expiratory volume in 0.5 second (FEV0.5) was determined using the raised volume rapid thoracic comp ression technique. Multivariate regression analysis was used to analyze the relationships between the lung function parameters and length. Both airway and tissue parameters showed a decreasing quadratic relationship with incr easing length. FEV0.5 showed an increasing cubic relationship with length. A family history of asthma was found to have a negative effect on Raw, H, a nd FEV0.5.