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Use of reactance to estimate transpulmonary resistance

¹ Dept of Respiratory Medicine, Glasgow Royal Infirmary, Glasgow, and ² Dept of Clinical Physics, Royal London Hospital, London, UK

CORRESPONDENCE: M. K. Johnson, Dept of Respiratory Medicine, Gartnavel General Hospital, 1053 Great Western Road, Glasgow, G12 0A, UK. E-mail: johnson7@which.net

Keywords: Airway hyperresponsiveness, airway obstruction, forced oscillation technique, resistance

Received: July 9, 2004
Accepted February 2, 2005

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.

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				M. K Johnson, M. Birch, R. Carter, J. Kinsella, and R. D Stevenson Measurement of physiological recovery from exacerbation of chronic obstructive pulmonary disease using within-breath forced oscillometry Thorax, April 1, 2007; 62(4): 299 - 306. [Abstract] [Full Text] [PDF]