A Study of the Effects of Airway Carbon Dioxide (PawCO2) on Superior Laryngeal Nerve Afferents Using an Isolated, Artificially Ventilated Closed Laryngeal Preparation in the Anaesthetized Cat

Abstract

Boushey et al. (1974) reported that changing intralaryngeal PCO2 could modify the discharge of single sensory fibres of the superior laryngeal nerve (SLN) in the anaesthetized cat. In their study the larynx was opened in the ventral midline and warmed humidified mixtures of CO2 in air were blown over the exposed laryngeal mucosa. This “open larynx” preparation permitted precise location and categorization of mucosal mechanoreceptors and excluded from study receptors sited deeper in the tissues of the larynx. However, the preparation was not subject to the pressures, airflows, and temperature changes associated with a normal respiratory cycle, stimuli which have been demonstrated to be responsible for the respiratory-related activity of SLN afferent fibres (Sant’Ambrogio et al., 1983, 1985a; Mathew et al., 1984). We decided, therefore, to develop an isolated, artificially ventilated “closed” laryngeal preparation to examine the effects of changing airway CO2 tension (PawCO2) on the responses of SLN sensory fibres to stimuli associated with a normal respiratory cycle.