Laryngeal muscle and diaphragmatic activities in conscious dog pups

A new chronic animal preparation (i.e. puppies) for the study of respiratory laryngeal muscle activity is described. Posterior cricoarytenoid (PCA), thyroarytenoid (TA) and diaphragmatic activities were monitored in conscious puppies (13-43 days old) using chronically implanted electrodes. PCA activity was prominent during inspiration in all behavioral states. TA and post-inspiratory diaphragmatic activities were consistently high during expiration in quiet wakefulness and quiet sleep, but expiratory TA activity decreased dramatically and post-inspiratory diaphragmatic activity became highly variable in rapid eye movement sleep. There was also a tendency for these expiratory muscle activities to become less pronounced with increasing postnatal age. When a chronically implanted, low resistance T-tube tracheal cannula was suddenly opened, thus effectively eliminating the effects of upper airway resistance on airflow, respiratory frequency dramatically increased. These results indicate that the puppy exhibits muscle activities consistent with the maintenance of an elevated end-expiratory lung volume achieved by the retardation of expiratory airflow using the larynx and diaphragm.