Studies on the central effects of Hering-Breuer reflexes

In our previous experiments performed with rabbits, it was found out that the strength of both inflation and deflation Hering-Breuer reflexes depends on the level of anaesthesia and ventilation as correlative factors in spontaneously and artificially ventilated animals, though this dependence was quantitatively and qualitatively different in these two groups. On the basis of the recent evidence pointing to the rapidly conducting fibres and thus indirectly the pulmonary stretch receptors as the pathway along which both Hering-Breuer reflexes are transmitted, an attempt has been made to show how both parameters of ventilation are centrally controlled in response to afferent information concerning such mechanical factors as resistance and compliance of the respiratory system. The results presented seem to allow the following conclusions: (i) An important role may be ascribed to the pulmonary stretch receptors in transmission of both Hering-Breuer reflexes. (ii) In quiet breathing the central mechanisms of the Hering-Breuer inflation reflex are set to regulate tidal volume on the basis of analysis of the compliance of the respiratory apparatus at the given moment. Their role to the control of the respiratory frequency is of minor importance. (iii) The contribution of the pulmonary stretch receptors to the control of respiratory frequency is based on information about the resistance of the airways. This parameter influences the ratio of duration of the activity phase to silent phase in discharges of pulmonary stretch receptors.