The high speed interrupter technique to measure airway wall mechanics in infants

The overall aim of this work was to develop a non-invasive way of measuring high frequency input impedance in infants which enables airway wall mechanics to be studied in vivo during normal tidal breathing. The establishing forced oscillation technique and the novel high speed interrupter technique were used to measure high frequency input impedance in infants. After the technical development and validation of the techniques, the variability and reproducibility of the measurements were determined to be similar to other lung function techniques for this age group. Using both techniques, high frequency input impedance showed particular features, the so called anti-resonant frequencies. Similar to human adults, in these infants anti-resonances are also related to wave propagation phenomena but not to tissue properties. Measurements during bronchial challenge with methacholine showed that airway wall compliance crucially determines the wave propagation velocity in the infants airways.;In order to determine whether airway wall mechanics are different in infants with wheezing disorders, high frequency Zin was examined in wheezing infants in comparison to healthy infants. Infants with wheezing disorders had lower anti-resonant frequencies even when they were asymptomatic, indicating in airway wall mechanics. Such structural changes may be due to developmental differences, differences in airway smooth muscle function or may be induced by airway inflammation and airway remodelling.