Reflex effects on breathing of laryngeal denervation, negative pressure and SO2 in upper airways

Abstract Respiratory reflex effects of laryngeal denervation, negative pressure and SO 2 in upper airways were studied in anesthetized rabbits. (a) Inspiratory efforts with nasal occlusion had longer duration (T io ) and smaller diaphragm activity (Adi) than with tracheal occlusion.After secretion of superior laryngeal nerves (SLN) these differences disappeared: values with tracheal occlusion became similar to those with nasal occlusion before denervation. This suggests that laryngeal pressure receptors, firing at zero pressure and decreasing their discharge with negative pressures, increase central inspiratory activity. (b) After SO 2 T io , both with tracheal and nasal occlusion, increased even after laryngeal denervation, provided SO 2 flowed through nasa pathway. Hence, nose and/or rhinopharynx contain receptors affected by SO 2 . (c) After laryngeal denervation and S 2 T io was shorter with nasal than with tracheal occlusion, despite equal Adi. This, combined with the above findings, suggests two groups of pressure receptors in nose and/or rhinopharynx with opposite effects on inspiratory off-switch: one unaffected and the other probably blocked by SO 2 . (d) During nose breathing section of SLN produced only a slight decrease in mean inspiratory flow.