Re-evaluation of respiratory reflexes

Abstract

In cats anæsthetized with chloralose it was found that below about 18° C. the rhythmic pattern of discharge in low-threshold pulmonary stretch fibres is reversed in relation to the respiratory cycle. This reversed pattern is apparently responsible for the reversal of the Hering Breuer inflation reflex (Head's paradoxical reflex). Evidence favouring this is that reflex inhibition of respiration, produced by high frequency electrical stimulation of pulmonary stretch fibres applied against a background of low frequency stimulation, is converted to excitation between 9 and 11° C. Head's paradoxical reflex appears when the total discharge in low- and higher threshold pulmonary fibres during inflation becomes less than the total discharge in the former before inflation. A nomogram showing the relation between temperature and the peak frequency of a train of impulses in fibres of different conduction velocities is presented. The likely mechanism responsible for the quantitative variation of the inflation reflex (and its reversal) with temperature is given.