Respiratory effects of airflow through the upper airways in newborn kittens and puppies

Abstract

Kittens, puppies, cats, and dogs were anesthetized with pentobarbital sodium and tracheotomized. The ventilatory pattern was recorded before, during, and after the delivery of steady flows of room air of 20 or 50 ml X s-1 X kg-1 in the expiratory direction through a cannula inserted just below the larynx. In the newborn, a reduction in breathing frequency, mainly due to a prolongation of the expiratory time, and a decrease in tidal volume contributed to a reduction in minute ventilation particularly with the higher flows; in some instances apnea resulted. Small or no effects were observed in the adult. The ventilatory inhibition was still present when humidified 37 degrees C warmed airstreams were delivered, and it was unchanged when airflows of 4.9% CO21.5% O2–82.6% N2 were applied. After local anesthesia of the laryngeal region or after bypassing the larynx, the ventilatory inhibition disappeared. By closure of a nostril at any given airflow, the upper airway pressure was substantially increased; however, this maneuver did not enhance the respiratory depression. We conclude that airflow through the upper airways can inhibit ventilation in newborn kittens and puppies presumably through the stimulation of airflow-sensitive laryngeal receptors.