Effects of lung volume on airway resistance during induced constriction in papain-treated rabbits. Nagase, T., H. Matsui, E. Sudo, T. Matsuse, M. S. Ludwig, and Y. Fukuchi. Department of Geriatrics, Faculty of Medicine, University of Tokyo, Tokyo, Japan; and Meakins-Christie Laboratories and Royal Victoria Hospital, McGill University, Montreal, Quebec, H2X 2P2, Canada
APStracts 3:0047A, 1996.
It has been reported that both the elasticity of the cartilage and airway-parenchymal interdependence can modify shortening of the airway smooth muscle and airway narrowing during induced constriction. We hypothesized that induced softening of the cartilage could alter airway compliance and/or the forces of mechanical interdependence, resulting in an increased degree of airway narrowing in response to a contractile stimulus. To test this hypothesis, we compared the effects of changing lung volume on airway resistance (Raw) under baseline conditions and during methacholine (MCh)-induced constriction in papain-treated (n=6) and control rabbits (n=6). Using the alveolar capsule technique, Raw was directly measured under baseline conditions at different levels of end-expiratory transpulmonary pressure (PL= 4-12 cmH2O). Then, aerosolized MCh was delivered (0.2-25mg/ml) and measurements were performed at different levels of PL (4 and 12 cmH2O). From measured tracheal flow and tracheal and alveolar pressure in open-chested animals during mechanical ventilation (VT= 6ml/kg, f=1Hz), we calculated Raw by subtracting tissue from lung resistance. Papain treatment significantly increased Raw both under baseline conditions and after induced constriction. We found that increasing PL decreased Raw before and after MCh in both groups; however the effects of changing PL on Raw were less in papain-treated animals. These observations suggest that both cartilage elasticity and mechanical interdependence are important determinants of airway smooth muscle shortening. The observation that volume dependence of Raw was less in papain-treated animals is consistent with the hypothesis that papain effects significant changes in the parenchymal attachments. 

Received 1 March 1995; accepted in final form 10 January 1996.
APS Manuscript Number A231-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96