Pulmonary vagal innervation is required to establish adequate alveolar ventilation in the newborn lamb

Abstract

To investigate the effects of bilateral intrathoracic vagotomy on the establishment of continuous breathing and effective gas exchange at birth, we studied 8 chronically instrumented, unanesthetized, sham-operated and 14 vagotomized newborn lambs after a spontaneous, unassisted vaginal delivery. Fetal lambs were instrumented in utero to record sleep states, diaphragmatic electromyogram, blood pressure, arterial pH, and blood-gas tensions. Six of eight sham-operated lambs established effective gas exchange within 10 min of birth, whereas 12 of 14 vagotomized animals developed respiratory acidosis and hypoxemia (P = 0.008). Breathing frequency in vagotomized newborns was significantly lower during the entire postnatal period compared with sham-operated newborns. Vagotomized subjects also remained hypothermic during the entire postnatal period (P < 0.05). Bronchoalveolar lavage indicated an increased minimum surface tension, whereas lung histology showed perivascular edema and partial atelectasis in the vagotomized group. We conclude that stimulation of breathing and effective gas exchange are critically dependent on intact vagal nerves during the transition from fetal to neonatal life.

Origins of the inhibiting effects of nasal CPAP on nonnutritive swallowing in newborn lambs

“…This model offers several advantages over previously reported lamb models with bilateral vagotomy (14,25). On the one hand, video-assisted thoracic surgery allows for a much less aggressive intervention than the use of a standard thoracotomy.…”

Physiological Society Symposium – Vagal Control: From Axolotl to Man

“…Their studies during the immediate newborn period showed that denervated animals were unable to establish adequate pulmonary gas exchange and breathing patterns, and remained hypothermic for the entire duration of study, despite supplemental heating. Arterial pH in the denervated animals remained at or below 7.1 and arterial Pco, (Pc,,co,) steadily increased to 70-80 mmHg, whereas the arterial Pd,02 remained near fetal values (Wong et al 1998). In contrast, the sham-operated group was able to establish pulmonary gas exchange and acid-base balance within the neonatal physiological range.…”

“…In contrast, shamoperated animals established effective alveolar ventilation. Since Wong et al (1998) performed vagal denervation 10-14 days prior to birth it is difficult to establish whether the effects of denervation on breathing patterns and gas exchange were of developmental (prenatal) origin or whether respiratory failure at birth reflects the critical importance of vagal afferents during the neonatal period in controlling expiratory braking and lung volume as shown previously (Fisher et al 1982;Praud et al 1992;England & Miller, 1995;Kianicka et al 1998). Intrathoracic vagal denervation and neural respiratory control during the early neonatal period.…”

“…Histological examination using both light and electron microscopy showed mild perivascular pulmonary oedema and partial atelectasis in the denervated group. However, normal type I1 epithelial cells containing lamellar bodies and tubular myelin were present in both sham-operated and denervated animals (Wong et al 1998). …”

“…The possible mechanisms of postnatal impaired gas exchange, consisting of severe hypoxaemia and respiratory acidosis in the prenatal vagally denervated animals, have been discussed previously (Wong et al 1998; and include a lack of increase in pulmonary blood flow normally observed at birth and surfactant system dysfunction. More importantly, the denervated newborns were unlikely to establish a normal postnatal FRC, which is dependent on frequent expiratory braking mediated via vagal afferents (Mortola & Gautier, 1995).…”