LARYNGEAL AND DIAPHRAGMATIC ACTIVITIES WITH A SINGLE EXPIRATORY LOAD IN NEWBORN LAMBS

Expiratory resistive loads elicit compensatory reflexes in the neonate which regulate end-expiratory lung volume (EEV). This study investiga ted the coordination of laryngeal and diaphragmatic activities when aw ake neonatal lambs were exposed to a single breath expiratory resistiv e load. The lambs were chronically instrumented for recording trans-up per airway pressure and electromyographic signals from the posterior c ricoarytenoid, thyroarytenoid, and diaphragm. The lambs breathed throu gh a sealed face mask connected to a pneumotachograph and non-rebreath ing valve with a loading manifold connected to the expiratory port. Si ngle breath expiratory loads produced, decreased airflow; prolongation s of PCA EMG activity and diaphragm EMG inhibition; decreased trans-up per airway resistance and increased EEV. In the post-load breath, insp iratory volume decreased, expired volume increased, and EEV returned t owards control baseline. Thus, neonatal lambs compensate for a single breath expiratory load by dilating the larynx and prolonging expirator y time. In the post-load breath, integrated activities of laryngeal an d diaphragmatic muscles, coupled with mechanical factors return EEV to wards baseline. (C) 1997 Elsevier Science B.V.