The sniff-like aspiration reflex evoked by electrical stimulation of the nasopharynx.

Forced inspiratory efforts resembling the sniff-like aspiration reflex (AR) were evoked by single-shocks or trains of electrical impulses to the dorsal pharyngeal and nasal mucosal surfaces in 12 anaesthetized spontaneously breathing cats. The strongest ARs determined by diaphragmatic (DIA) EMG and peak-inspiratory flows were elicited from the dorsolateral nasopharyngeal wall close to the torus tubalis. Highly responsive sites were also detected in the posterolateral nasal cavity and in the rostrolateral oropharynx. Repetitive stimulation at threshold strength evoked ARs exclusively in the late inspiration and early expiration. Suprathreshold responses abolished and replaced the tidal respiration. ARs exhibited a two-phase response in DIA EMG: a short latency (25.2 +/- 2.4 msec, M +/- SD) powerful excitation (69.7 +/- 10.7 msec) followed by an voltage-dependent inhibition (63.9 +/- 11.3 msec). Irrespective of voltage repetitive ARs were attenuated at rates above 7-9 Hz. In conclusion, electrical stimulation within the large receptive area of the nasal-pharyngeal airway evokes sniff-like efforts with biphasic inspiratory pattern and marked phase-dependent properties.