Breathing patterns, pulmonary mechanics and gas exchange: role of vagal innervation in neonatal lamb.

Abstract

Although vagal afferents are active during intrauterine life, vagal denervation does not lead to gross changes in the occurrence of fetal breathing movements. However, lack of volume feedback has profound and deleterious effects on pulmonary compliance and impairs gas exchange during the early neonatal period. Intrathoracic vagal denervation, which spares vocal cord paralysis and upper airway obstruction in spontaneously breathing unanaesthetised neonatal lambs, leads to reduced pulmonary compliance and persistent hypoxaemia. The underlying mechanisms of these adverse effects include slow breathing frequency, prolonged expiratory times, decreased augmented breaths and the inability to maintain dynamic functional residual capacity leading to progressive atelectasis and regional ventilation- perfusion mismatch. Our data suggest that intrathoracic vagal denervation does not lead to pulmonary oedema in newborn lambs which most probably occurred because of upper airway obstruction in previous studies. We provide evidence that the vagal afferent fibre-receptor system provides critical feedback for the maintenance of normal breathing patterns and pulmonary gas exchange during the early neonatal period. Experimental Physiology (2001) 86.6 , 803-810.