Nasal 'pressure' receptors.

This study was performed to identify, recording from single fibers of the ethmoidal nerve, nasal receptors which respond to changes in the upper airway pressure during nasal occlusion. In 15 anaesthetized rats breathing through the nose, three consecutive nasal occlusions were performed while recording the afferent activity of ethmoidal nerve fibers, the EMG activity of an external intercostal muscle, temperature in the nose and upper airway pressure. Twenty-two afferent fibers were activated during the three inspiratory efforts with occlusions applied at end-expiration, when the upper airway was subjected to negative pressure (-1.93, -2.16 and -2.22 kPa at the 1st, 2nd and 3rd effort, respectively). The number of impulses was 24, 22 and 20 (n = 22) at the 1st, 2nd and 3rd effort, respectively. The pressure threshold were measured as -0.73, -0.87 and -0.96 kPa (n = 22) in each effort. Three fibers were also stimulated by positive pressure during occlusions performed at end-inspiration. In 5 rats breathing through a tracheostomy, maintained negative (-0.1-3.7 kPa) and positive (0.8-3.0 kPa) pressures were applied to the isolated upper airway. All the 12 fibers tested were activated by the maintained negative pressure, whereas three of them were also activated by the maintained positive pressure. However, none of fibers tested were stimulated by tracheal occlusions. These results indicate that the ethmoidal branch of the trigeminal nerve contains fibers connected to nasal 'pressure' receptors, mostly 'negative pressure' receptors, that may play a role in the maintenance of upper airway patency.