Correction of thermal artifacts in plethysmographic airway
resistance measurements.
Peslin, R., C. Duvivier, P. Malvestio, and A. R. Benis.
Unit 14 de Physiopathologie Respiratoire, Institut National de la
Sant et de la Recherche Mdicale Universit Henri Poincar Nancy I,
54500 Vandoeuvre-les-Nancy, France
APStracts 3:0080A, 1996.
Specific airway resistance (sRaw), measured by body plethysmography
without conditioning of the inspired air to BTPS, exhibits a strong
frequency dependence related to the fact that the warming and wetting
of the gas in the airways is not instantaneous (Peslin et al., J.
Appl. Physiol., under press). We have tested in 21 healthy subjects
three methods to correct for that artefact, using a simple model
assuming a first order thermal process characterized by a single time
constant (Q). The corrections required entering an assumed constant
value for Q (methods 1 and 2) and/or for airway inertance (Iaw)
(methods 1 and 3), and/or measuring the inspired gas temperature and
water vapor saturation (methods 2 and 3). The frequency dependence of
sRaw was measured from 0.5 to 3 Hz both with (sRawbtps) and without
(sRawamb) gas conditioning. With optimal values for Q and/or Iaw, the
mean difference between sRawamb and sRawbtps was close to zero with
all three methods, but the root-mean-square difference was
significantly lower with method 2 (0.83+/-0.35 hPa.s compared to
1.21+/-0.54 and 1.20+/-0.49 hPa.s with methods 1 and 2,
respectively). We conclude that the thermal artefact of sRaw
measurements may be best corrected using temperature measurements and
an assumed time constant (0.152 s with our equipment).
Received 28 September 1995; accepted in final form 19 January
1996.
APS Manuscript Number A1051-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 8 February 96