Laryngeal receptors responding to transmural pressure, airflow and local muscle activity.

The larynx has a rich sensory supply which is the main source of several respiratory reflexes. These reflexes, that influence both the patency of the upper airway and the pattern of breathing, are related to transmural pressure and/or airflow in the upper airway. Yet hardly any information is available on the response of laryngeal mechanoreceptors to transmural pressure and airflow. We recorded action potentials from single fibers separated from the superior laryngeal nerve of anesthetized dogs, breathing spontaneously either through a tracheostomy or the upper airway. The airway could be occluded above or below the larynx. On the basis of their behavior during tracheostomy breathing, upper airway breathing, tracheal occlusion and upper airway occlusion, laryngeal mechanoreceptors were classified as pressure receptors, flow receptors or 'drive' receptors (stimulated by the respiratory activity of upper airway muscles). Pressure receptors were encountered most frequently, representing 63.6% of our sample of 110 receptors, 'drive' receptors constituted 21.8% and flow receptors the remaining 14.6%. Our findings indicate that, even though the three types of receptors differ in sensory modality, they concur in exhibiting a predominant activity during inspiration. In fact, 65% of all receptors are active during eupneic inspiration. Moreover, their activity increases markedly during upper airway obstruction.