APStracts 2:0070A, 1995.

Lung and respiratory impedance at low frequency during mechanical ventilation in rabbits. Rotger, M., R. Peslin, D. Navajas, and R. Farr[acute]e. Lab. Biofisica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona, Spain, and Unit[acute]e 14 de Physio-pathologie Respiratoire, Institut National de la Sant[acute]e et de la Recherche M[acute]edicale. Vandoeuvre-les-Nancy, France

APStracts 2:0070A, 1995.

We have tested in eight rabbits the feasibility of measuring respiratory (Zrs) and lung (Zl) impedances in the low frequency domain, including below the breathing frequency (Fr), during conventional mechanical ventilation (CMV). The animals were tracheotomized and ventilated with a tidal volume (Vt) of 20 ml at a Fr of 1 Hz. The excitation signal was provided by a flow generator connected in parallel with the ventilator ; it included six components ranging from 0.45 Hz to 14.8 Hz, which met the neither -sum-nor-difference criterion of Suki et al. (IEEE Trans. Biomed. Eng., 39: 1142-1151, 1992) to minimize the influence of non -linearities. Zrs and Zl were also measured at the same mean lung volume and with the same excitation signal both during apnea and when the ventilator signal was replaced by a sinewave with the same Vt and Fr (SMV). The real parts (Re) of both Zrs and Zl, as well as the effective elastances, were significantly larger during apnea than during CMV and SMV over the whole frequency range. Re(Zrs) and Re(Zl) were similar during CMV and SMV above Fr but they were lower during CMV at 0.45 Hz. The latter difference seems to be related to the presence of harmonics of Fr and of additional frequency components due to pulse amplitude modulation. We conclude that, due to non -linearities, it is feasible to measure Zrs and Zl during CMV only at and above Fr.

Received 7 September 1994; accepted in final form 16 February
1995.
APS Manuscript Number A939-4.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  1 March 1995.