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Thorax 2001;56:42-47 doi:10.1136/thorax.56.1.42
  • Original article

Methacholine responsiveness in infants assessed with low frequency forced oscillation and forced expiration techniques

  1. G L Halla,d,
  2. Z Hantosa,b,
  3. J H Wildhaberc,
  4. F Petáka,b,
  5. P D Slya,d
  1. aDivision of Clinical Sciences, Institute for Child Health Research, Perth, Australia, bDepartment of Medical Informatics and Engineering, University of Szeged, Szeged, Hungary, cDepartment of Respiratory Medicine, University Children's Hospital, Zürich, Switzerland, dCentre for Child Health Research, University of Western Australia, Perth, Australia
  1. Dr G L Hall, Respiratory Medicine, University Children's Hospital, Steinwiesstrasse 75, Zürich, CH-8032, Switzerlandgraham.hall{at}kispi.unizh.ch
  • Received 2 May 2000
  • Revision requested 16 June 2000
  • Revised 6 October 2000
  • Accepted 6 October 2000

Abstract

BACKGROUND The contribution of the pulmonary tissues to the mechanical behaviour of the respiratory system is well recognised. This study was undertaken to detect airway and lung tissue responses to inhaled methacholine (Mch) using the low frequency forced oscillation technique (LFOT).

METHODS The respiratory system impedance (Zrs, 0.5–20 Hz) was determined in 17 asymptomatic infants. A model containing airway resistance (Raw) and inertance (Iaw) and a constant phase tissue damping (G) and elastance (H) was fitted to Zrs data. Tissue hysteresivity (η) was calculated as η=G/H. The raised volume rapid thoracic compression technique (RVRTC) was used to generate forced expiratory volume in 0.5 seconds (FEV0.5). Lung function was determined at baseline and following inhaled Mch in doubling doses (0.25–16 mg/ml) until the maximal dose was reached or a fall of 15% in FEV0.5 was achieved (PC15FEV0.5). The response to Mch was defined in terms of the concentration of Mch provoking a change in lung function parameters of more than two standard deviation units (threshold concentration).

RESULTS At PC15FEV0.5 a response in Raw, Iaw, G, and η, but not H, was detected (mean (SE) 61.28 (12.22)%, 95.43 (34.31)%, 46.28 (22.36)%, 44.26 (25.83)%, and –6.48 (4.94)%, respectively). No significant differences were found between threshold concentrations of LFOT parameters and FEV0.5.

CONCLUSIONS Inhaled Mch alters both airway and respiratory tissue mechanics in infants.

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