Methacholine responsiveness in infants assessed with low frequency forced oscillation and forced expiration techniques
G L Halla d, Z Hantosa b, J H Wildhaberc, F Petáka b, P D Slya d
a Division of Clinical
Sciences, Institute for Child Health Research, Perth, Australia, b Department of Medical Informatics and
Engineering, University of Szeged, Szeged, Hungary, c Department of Respiratory
Medicine, University Children's Hospital, Zürich, Switzerland, d Centre
for Child Health Research, University of Western Australia, Perth,
Australia
Correspondence to: Dr G L Hall, Respiratory Medicine, University Children's Hospital, Steinwiesstrasse 75, Zürich, CH-8032, Switzerland graham.hall{at}kispi.unizh.ch
Received 2 May 2000; Returned to authors 16 June 2000; Revised version received 6 October 2000; Accepted for publication 6 October 2000
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).
METHODSThe
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 (
) was calculated
as =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).
RESULTSAt
PC15FEV0.5 a response in Raw, Iaw, G, and ,
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.
CONCLUSIONSInhaled
Mch alters both airway and respiratory tissue mechanics in infants.
Keywords: forced oscillations; airway mechanics; lung tissue mechanics; children
© 2001 by Thorax
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