Reversal of apnoea by aspiration reflex in anaesthetized cats

Various flow and timing characteristics of breathing as well as electrocorticographic (ECoG) records were analysed in a model of reversible respiratory failure induced by N2 inhalation in 27 anaesthetized cats. During the first minute of respiratory arrest, nasopharyngeal stimulation by an elastic nylon fibre elicited a typical sniff- or gasp-like aspiration reflex (in 88.8% of cases), whilst similar tracheobronchial irritation evoked a weak cough reaction in one third of cases (34.2%). The aspiration reflex could also be evoked in progressive stages of apnoea characterized by very low and even isoelectric ECoG activity immediately before imminent irreversible respiratory failure, and it could interrupt and replace the periodic gasping sometimes occurring during apnoea. The reflex, comprising powerful inspiration efforts, could be evoked during apnoea many times in succession. Repeated aspiration reflexes alone resulted in recovery from hypoxic apnoea with gradual normalization of ECoG and subsequent restitution of spontaneous breathing even more frequently than it occurred in periodic gasping. Successful resuscitation from hypoxic apnoea by the aspiration reflex in cats suggests that nasopharyngeal stimulation can affect the mechanisms underlying the failure and restitution of breathing at least in some forms of apnoea.