Multiple-breath washout and washin experiments in steers.
Rollin, F., D. Desmecht, S. Verbanck, A. Van Muylem, P. Lekeux, and M.
Paiva.
Laboratory for Functional Investigation, Faculty of Veterinary
Medicine, University of Li[grave]ege, 4000 Li[grave]ege, Belgium;
Department of Pneumology, Academisch Ziekenhuis, Biomedical Physics
Laboratory and Chest Service, Free University of Brussels, 1070
Brussels, Belgium
APStracts 3:0178A, 1996.
Multiple-breath N2 washouts (WO) and washins (WI) were performed
during regular tidal breathing in 11 unsedated healthy steers
approaching pulmonary functional maturity (mean body weight = 271
kg). They inspired 20% O2 in 80% Ar during the WO and air during the
WI. For each steer, we computed two indices of ventilation
inhomogeneity from the N2 WO curves : (a) the curvilinearity of the
logarithm of end-tidal N2 concentrations (FetN2) as a function of
cumulative expired volume (SVe) reflected in the ratio of two slopes
fitted between 100% and 50% and between 50% and 10% respectively of
FetN2 of the first breath of the WO, (b) the N2 phase III slope
divided by the mean expired concentration (Sn) of each breath also
plotted as a function of SVe. Equivalent computation of both
parameters was done on WI and WO curves, and similar results were
obtained. The mean slope ratio was 0.812 +/- 0.119 (SD) for all the
steers, which is consistent with topographical gravity-dependent
specific ventilation distribution inhomogeneity. Sn was independent
of the breath number n both for WO and WI (mean Sn = 0.130 +/- 0.057
L-1), suggesting that emptying between unequally ventilated units is
synchronous. This behavior resembles that observed in rats postmortem
(Verbanck et al., J. Appl. Physiol. 71 : 847-854, 1991) but contrasts
with experiments in human beings, where convection-dependent
ventilation inhomogeneities generate a marked increase in Sn
throughout the entire WO (Crawford et al., J. Appl. Physiol. 59 :
838-846, 1985). This is surprising, as one would expect gravity
-dependent sequential emptying in animals of this size.
Received 5 July 1995; accepted in final form 15 March 1996.
APS Manuscript Number A715-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 16 April 96