Multiple-breath washout and washin experiments in steers.
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 indexes of ventilation inhomogeneity from the N2 WO curves: 1) the curvilinearity of the logarithm of end-tidal N2 concentrations as a function of cumulative expired volume reflected in the ratio of two slopes fitted between 100 and 50% and between 50 and 10%, respectively, of end-tidal N2 concentration of the first breath of the WO; and 2) the N2 phase III slope divided by the mean expired concentration (Sn) of each breath also plotted as a function of cumulative expired volume. 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 topographic gravity-dependent specific ventilation distribution inhomogeneity. Sn was independent of the breath number both for WO and WI (mean Sn = 0.130 +/- 0.057 liters-1), suggesting that emptying between unequally ventilated units, is synchronous. This behavior resembles that observed in rats postmortem (S. Verbanck, E.R. Weibel, and M. Paiva. J. Appl Physiol. 71: 847-854, 1991) but contrasts with experiments in humans, in whom convection-dependent ventilation inhomogeneities generate a marked increase in Sn throughout the entire WO (A. B. H. Crawford, M. Makowska, M. Paiva, and L. A. Engel. J. Appl. Physiol. 59: 838-846, 1985). This is surprising because one would expect gravity-dependent sequential emptying in animals of this size.
Rollin
F
F
Laboratory for Functional Investigation, Faculty of Veterinary Medicine, University of Liège, Belgium.
Desmecht
D
D
Verbanck
S
S
Van Muylem
A
A
Lekeux
P
P
Paiva
M
M
D000818:Animals; D001128:Argon / Q000737:chemistry; D002417:Cattle; D018481:Convection; D004947:Esophagus / Q000502:physiology; D006112:Gravitation; D008168:Lung / Q000033:anatomy & histology / Q000502:physiology*; D008297:Male; D009584:Nitrogen / Q000737:chemistry; D012123:Pulmonary Ventilation / Q000502:physiology; D051381:Rats; D015656:Respiratory Mechanics / Q000502:physiology*; D013990:Tidal Volume
D001128:Argon; D009584:Nitrogen