Use of reactance to estimate transpulmonary resistance

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Abstract
This study examines the relationship of respiratory system resistance (Rrs) and reactance (Xrs) measured by forced oscillometry with transpulmonary resistance (RL) measured by oesophageal manometry.Simultaneous forced oscillometry using a single frequency of 5 Hz and oesophageal manometry were performed on five asthmatics during bronchoprovocation. The data obtained were used to derive prediction equations forRLfrom oscillometric parameters, which were tested on a further six asthmatics and 35 nonasthmatic subjects.In the first five asthmatic subjects,RLcorrelated more strongly withXrsthan withRrs. In the second set of asthmatics,RLranged 0.0005–4.57 kPa·s·L−1, with a median of 0.21 kPa·s·L−1. TheRLvalues predicted fromXrsshowed a mean±sddifference of −0.067±0.25 kPa·s·L−1compared with the values measured in this set of patients.Xrsin subjects with other respiratory conditions appeared to follow the same relationship withRLas in asthmatics. Lumped element modelling suggested that the linear relationship betweenXrsandRLwas a consequence of the increasing contribution of central and upper airway wall shunts as peripheral airway resistance rose, and that this effect was much larger than that due to changes in static elastance.In conclusion, the reactance of the respiratory system can predict transpulmonary resistance more accurately than can the resistance of the respiratory system.