Use of reactance to estimate transpulmonary resistance.

This study examines the relationship of respiratory system resistance (R(rs)) and reactance (X(rs)) measured by forced oscillometry with transpulmonary resistance (R(L)) 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 for R(L) from oscillometric parameters, which were tested on a further six asthmatics and 35 nonasthmatic subjects. In the first five asthmatic subjects, R(L) correlated more strongly with X(rs) than with R(rs). In the second set of asthmatics, R(L) ranged 0.0005-4.57 kPa.s.L(-1), with a median of 0.21 kPa.s.L(-1). The R(L) values predicted from X(rs) showed a mean+/-sd difference of -0.067+/-0.25 kPa.s.L(-1) compared with the values measured in this set of patients. X(rs) in subjects with other respiratory conditions appeared to follow the same relationship with R(L) as in asthmatics. Lumped element modelling suggested that the linear relationship between X(rs) and R(L) was 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.