Vagal influence on respiratory mechanics in newborn kittens

The aim of this study was to investigate the effects of pulmonary vagal innervation on respiratory mechanics of the newborn kitten. To this end, eight kittens in the first week of life were anaesthetized, tracheostomized and measurements of breathing pattern and respiratory mechanics compared between the intact and post-vagotomy condition. Airflow (V) and changes in lung volume (V) were measured with a pneumotachograph attached to the tracheal cannula; tracheal pressure (Ptr) was measured from a side-port of the cannula. Pressure in the oesophagus (Pes), representing the mean pleural pressure (Ppl), was recorded using a liquid filled catheter. By occluding the airway at end-inspiration, static respiratory system compliance (Crs), chest wall (Cw), and lung compliance (CL) were computed as the ratio of V over, respectively, Ptr, Pes and Ptr-Pes. The slope of the relationship between V and V during expiration represented the respiratory system time constant (tau rs), from which the resistance of the respiratory system was obtained (Rrs = tau rs/Crs). Dynamic lung compliance (Cdyn) and total pulmonary resistance (TPR) were obtained from the V, V and Ppl values during spontaneous breathing. After bilateral cervical vagotomy, most of the variables pertinent to respiratory mechanics did not change significantly, but Cw increased (35%) and TPR decreased (12%). The former probably resulted mainly from the deeper post-vagotomy breathing pattern, the latter from a loss in bronchomotor tone. Both the work per breath and the work per minute, computed as proposed by OTIS et al., tended to increase after vagotomy because of the deeper tidal volume, more than offsetting the changes in pulmonary mechanics.(ABSTRACT TRUNCATED AT 250 WORDS)