SNIFF-LIKE ASPIRATION REFLEX EVOKED BY PRESSURE PULSES FROM THE UPPERAIRWAYS IN CATS

Respiratory effects of single positive and negative pressure pulses (P PP, NPP) applied to the functionally isolated upper airways (UA) were studied in 11 anaesthetized cats breathing spontaneously through a tra cheal tube. The UA pressure and the changes of tracheal airflow were r ecorded and the blood pressure and electrocardiogram were occasionally monitored. Sniff-like aspiration reflexes comprising powerful spasmod ic inspirations could be elicited by PPP or NPP of 20 to 110 cm H2O or -14 to -140 cm H2O. The responses to NPP but also to PPP characterize d by high peak inspiratory flow, mean inspiratory flow and tidal volum e (PIF = 312.5 +/- 64.3 and 231.1 +/- 21.7 ml.sec(-1); ($) over bar VT I = 178.3 +/- 46.7 and 110.1 +/- 14.4 ml.sec(-1); VT = 40.9 +/- 8.3 an d 22.5 +/- 1.7 ml) resembled closely the aspiration reflex elicited by mechanical stimulation of the pharyngeal wall. Occasionally, sneezing , minor modifications of breathing pattern and solitary forced inspira tions could be induced by lower pressures. The results indicate that s udden pressure stimulation of the UA evokes vigorous respiratory respo nses including the aspiration reflex. These reflexes and their alterat ions may contribute to development or release of both UA obstruction a nd apnoea, at least in cats.