Importance of Upper Airway Airflow in the Ventilatory Depression of Laryngeal Origin

Abstract

Summary: Flows of air through the upper airway depress ventilation, particularly in newborns. This reflex response can be due to changes in upper airway pressure and/or upper airway airflow. In order to investigate the separate role of these two factors, we have studied four adult cats and three newborn kittens anaesthetized with pentobarbital. The animals were spontaneously breathing through a tracheostomy placed low in the neck. A second cannula located just below the larynx could be connected to a steady airflow source or to a pressurized jar. During the delivery of upper airway airflows, tidal volume, frequency and ventilation were decreased. When static pressures of values similar to those measured during the delivery of the airflows were applied, no depression of the ventilatory parameters was observed. We conclude that dynamic flow dependent factors are required for the ventilatory inhibition originating from the upper airways.