Ventilation in kittens with chronic section of the superior laryngeal nerves

The breathing pattern of conscious newborn kittens one-to-two weeks old was studied by the barometric method about 5 days after bilateral section of the superior laryngeal nerve (SLN-denervated group) or a sham operation (SLN-sham operated group). None of the ventilatory variables differed between the two groups, whether during normoxia or acute hypoxia (10 min of 10% O2). After anesthesia, delivery of steady airflows in the expiratory direction through the upper airways of the SLN-sham operated had marked inhibitory effects on ventilation which entirely disappeared after SLN section. A small inhibition was still present in the SLN-denervated group, possibly indicating that other non-SLN upper airways receptors developed inhibitory ventilatory effects during the period of chronic denervation. Intermittent expiratory upper airway airflows were much less effective than steady flows and no inhibition was seen with oscillatory flows, indicating that the mode of application of the stimulus to the laryngeal receptors is crucial in determining the magnitude of their reflex response. Under anesthesia, acute bilateral section of the SLN determined a small increase of the integrated peak EMG activity of the diaphragm. We conclude that laryngeal SLN afferents are inhibitory on ventilation in newborn kittens, but this effect is very small during normal conscious conditions. Only under special circumstances, including anesthesia and sustained upper airways flows and pressures, the ventilatory inhibition can be disproportionately magnified.