Effects of topical nasal anaesthesia on shift of breathing route in adults

The position of the soft palate is known to determine the breathing route, but the physiological mechanisms that bring about a shift from nasal to oral breathing are unclear. To test the hypothesis that activation of receptors in the nasal passage may be involved in reflex initiation of oral breathing after nasal obstruction, we investigated respiratory responses to nasal occlusion before and after topical lignocaine anaesthesia of the nasal passages. Eleven volunteers were fitted with custom-made partitioned face masks, which separated nasal and oral passages. Air flow through each passage was detected by changes in airway pressure and carbon dioxide concentration. Nine subjects were habitual nasal breathers both before and after topical anaesthesia with 4% lignocaine. Among these subjects, the time to initiate oral breathing in response to nasal occlusion was significantly shorter before anaesthesia than afterwards (mean 4.4 [SD 2.5] vs 10.8 [7.4] s, p less than 0.01). Similarly, the time to resume nasal breathing after release of nasal occlusion was significantly shorter before topical anaesthesia than afterwards (6.9 [4.9] vs 12.1 [7.8] s, p less than 0.01). Topical anaesthesia did not affect respiration rate, end-tidal carbon dioxide concentration, or arterial oxygen saturation. These findings suggest that in human beings sensory information from receptors in the nasal passage has an important role in controlling the shift of breathing route.