APStracts 3:0374A, 1996.

Effect of expiratory flow limitation on respiratory mechanical impedance. a model study. Peslin, R., R. Farr, M. Rotger, and D. Navajas. Lab. Biofisica i Bioenginyeria, Facultat de Medicina, Universitat de Barcelona, Spain, and Unit 14 de Physiopathologie Respiratoire, Institut National de la Sant et de la Recherche Mdicale, Universit Henri Poincar Vandoeuvre -les-Nancy, France

APStracts 3:0374A, 1996.

Large phasic variations of respiratory mechanical impedance (Zrs) have been observed during induced expiratory flow limitation (EFL) (Vassiliou et al., Eur. Respir J., under press). To clarify the meaning of Zrs during EFL, we have measured from 5-30 Hz the input impedance (Zin) of mechanical analogs of the respiratory system including flow limiting elements (FLE) made of easily collapsible rubber tubing. The pressure upstream (Pus) and downstream (Pds) from the FLE were controlled and systematically varied. Maximal flow (max) increased linearly with Pus, was close to the value predicted from wave-speed theory, and was obtained for Pus-Pds of 4-6 hPa. The real part (Re) of Zin started increasing abruptly with flow above 85 % max, and either further increased or suddenly decreased in the vicinity of max. The imaginary part of Zin decreased markedly and suddenly above 95 % max. Similar variations of Zin during EFL were seen with an analog which mimicked the changes of airway transmural pressure during breathing. Combining pressure and flow measurements upstream and downstream from the FLE, the latter was analyzed in terms of a serial (Zs) and a shunt (Zp) compartment. Zs was consistent with a large resistance and inertance, and Zp with a mainly elastic element having an elastance close to that of the tube walls. We conclude that Zrs data during EFL mainly reflect the properties of the FLE.

Received 2 May 1996; accepted in final form 23 July 1996.
APS Manuscript Number A423-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 21 August 1996