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 investigated the coordination of laryngeal and diaphragmatic activities when awake neonatal lambs were exposed to a single breath expiratory resistive load. The lambs were chronically instrumented for recording trans-upper airway pressure and electromyographic signals from the posterior cricoarytenoid, thyroarytenoid, and diaphragm. The lambs breathed through a sealed face mask connected to a pneumotachograph and non-rebreathing valve with a loading manifold connected to the expiratory port. Single breath expiratory loads produced, decreased airflow; prolongations of PCA EMG activity and diaphragm EMG inhibition; decreased trans-upper airway resistance and increased EEV. In the post-load breath, inspiratory volume decreased, expired volume increased, and EEV returned towards control baseline. Thus, neonatal lambs compensate for a single breath expiratory load by dilating the larynx and prolonging expiratory time. In the post-load breath, integrated activities of laryngeal and diaphragmatic muscles, coupled with mechanical factors return EEV towards baseline.