Comparison of four methods of assessing airflow resistance before
and after induced airway narrowing in normal subjects.
Phagoo, Sb, Ra Watson, M Silverman, Nb Pride.
Departments of Paediatrics and Medicine, Royal Postgraduate Medical
School, Hammersmith Hospital, Du Cane Road, London W12 ONN
APStracts 2:0155A, 1995.
Four methods for assessing airflow resistance were compared in 7
normal adults at baseline and after inducing airway narrowing with
inhaled methacholine(Mch). Airway resistance(Raw) was measured during
panting at 1-2Hz within a body plethysmograph; total lung
resistance(RL) was measured using an oesophageal balloon during quiet
breathing(RLq) and with doubling of frequency (RLr) while maintaining
the original tidal volume; total respiratory resistance(Rrs) was
measured at 6Hz during forced oscillation applied at the airway
opening and interruption resistance(Rint) was measured at mid-tidal
expiratory flow. Three methods of obtaining Rint after airflow
interruption were compared (smooth curve fit of mouth pressure(Pmo)
back-extrapolated to valve closure, RintC; two-point linear fit of
Pmo back-extrapolated to 15ms following closure,RintL; Pmo at 100ms
after valve closure, RintEI). We found similar basal median
values(cmH2O.l-1.s) of Raw(1.3), RLq(1.4), RLr(1.9), Rrs(1.7) and
RintC(1.5); basal values of RintL(2.4) and RintEI(4.4) were
considerably larger. After induced airway narrowing all methods of
measuring resistance showed significant increases; these were largest
with RLq(median % change 265) and smallest with the three Rint
methods(median % change 62-72). Rint and Rrs methods had poorer
sensitivity for detecting bronchoconstriction than RL or Raw. Of the
Rint methods, RintEI was the most sensitive. We conclude that the
convenience of measuring Rrs and Rint is associated with a relative
lack of sensitivity in detecting induced airway narrowing.
Received 24 October 1994; accepted in final form 5 April 1995.
APS Manuscript Number A1090-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.