Influence of laryngeal CO2 on respiratory activities of motor nerves to accessory muscles.

Intralaryngeal CO2 in decerebrate, vagotomized cats decreases phrenic nerve activity and increases the respiratory activity of the hypoglossal (HG) nerve. These responses are mediated by afferents in the superior laryngeal nerves. To explore the responses of other respiratory motor nerves to this stimulus, we have recorded the activities of the nasolabial (NL) branch of the facial nerve, the posterior cricoarytenoid (PCA) and thyroarytenoid (TA) branches of the recurrent laryngeal nerve and the nerve to triangularis sterni (TS) muscle. In response to 5 and 10% CO2 in the surgically isolated upper airway, we found dose-related decreases in phrenic activity, increases in HG and NL activity and characteristic, but intermittent, exaggeration of early expiratory bursts of TA activity. The activities of the PCA and TS nerves showed no consistent responses. These results broaden the definition of the reflex response to intralaryngeal CO2, revealing components that reflect ventilatory inhibition, upper airway dilation and laryngeal protection.