Analysis of low-frequency lung impedance in rabbits with non-linear models. Peslin, R., C. Saunier, C. Duvivier, M. Marchand. Unit[acute]e 14 de Physiopathologie Respiratoire, Institut, National de la Sant[acute]e et de la Recherche M[acute]edicale., Universit[acute]e H. Poincar[acute]e Nancy I, 54500 Vandoeuvre-les -Nancy, France.
APStracts 2:0173A, 1995.
Lung mechanics was studied in six paralyzed, tracheotomized rabbits ventilated with a specially devised computer-controlled ventilator. The target flow waveform contained non-integer multiple frequencies ranging from 0.83 to 6-10 Hz, and met a neither-sum-nor-difference criterion to minimize the effects of non-linearity (Lutchen et al. J. Appl. Physiol. 75, 478-488, 1993). The actual flow, however, contained harmonics of the two lowest frequencies. Measurements were performed at mean airway pressure (MAP) of 8 and 12 hPa, and during histamine-induced bronchoconstriction. Smooth impedance curves were observed in unchallenged rabbits at low MAP. In contrast, unrealistic impedance fluctuations, suggestive of crosstalk from the unwanted frequency components in the flow input, were seen at high MAP and during acute bronchoconstriction. Model analysis was performed by using the actual flow signal as an input to various non-linear models. The impedance fluctuations observed at high MAP were well simulated by a model featuring a volume-dependent elastance, and those observed after histamine almost perfectly reproduced by a model where resistance increased with the reciprocal of lung volume. We conclude that impedance data biased by crosstalk may provide useful information on the presence and nature of respiratory system non -linearities. 

Received 26 September 1994; accepted in final form 14 April 1995.
APS Manuscript Number A998-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  2 May 1995.