CONTRIBUTION OF VAGAL AFFERENTS TO THE VOLUME-TIMING RESPONSE TO EXPIRATORY LOADS IN NEONATAL LAMBS

Expiratory loads elicit volume-dependent reflex increases in expirator y duration (T-E) in adult animals. This reflex is mediated by pulmonar y vagal afferents. It was hypothesized that this same reflex in newbor n lambs is mediated by vagal afferents. Single-breath graded expirator y loads were presented to 4 day old, anesthetized neonatal lambs throu gh a facemask (FM), via a tracheostomy (TR) and after the cervical vag i were severed bilaterally in the TR animals (VAG). In FM and TR studi es, expired volume (V-E) decreased and T-E increased with increasing l oad magnitude. There was no significant difference in the V-E-T-E curv es for FM and TR. These results demonstrate that pulmonary vagal affer ents are mediating the volume-related reflex modulation of T-E during expiratory loading in the anesthetized neonatal lamb which is unaffect ed by bypass (TR) of upper airway afferents.