Changes in end-expiratory lung volume and diaphragmatic activity during hypoxia and hypercapnia in cats. Bonora, M., and M. Vizek. Laboratoire de Physiologie Respiratoire, Facult[acute]e de M[acute]edecine St-Antoine, 75012 - Paris, France
APStracts 2:0338A, 1995.
To assess the role of diaphragmatic activity at the end of expiration (DE) in the control of end-expiratory lung volume (EELV) : 1. these two parameters were correlated in anesthetized cats breathing different gas mixtures; 2. expiratory flow volume curves in normoxia and hypoxia together with changes in esophageal pressure were measured. The influence of volume feed-back on DE control was tested by applying PEEP. The effect of anesthesia was determined by measuring DE in unanesthetized cats. In hyperoxia, DE (but not EELV) decreased. In hypocapnic hypoxia (12, 10 and 8%O2), both DE and EELV gradually increased and these changes were significantly correlated. When normocapnia was restored in 8%O2, DE and EELV decreased, but remained higher than in air. Hypercapnia affected neither DE nor EELV. PEEP blocked the hypoxia-induced increase in DE. Hypoxia decreased expiratory flow and esophageal pressure. Lastly, the increases in DE at 12 and 10%O2 were more pronounced when the cats were unanesthetized. These results suggest that the increase in diaphragmatic activity induced by hypocapnic hypoxia during expiration affects expiratory flow and thoracic volume, and therefore plays a major role in increasing EELV. This phenomenon may also be controlled by volume feedback. 

Received 31 March 1995; accepted in final form 24 July 1995.
APS Manuscript Number A353-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 10 August 1995.