HYPOXEMIA DOES NOT AFFECT THE STRENGTH OF THE INSPIRATION-INHIBITING BREUER-HERING REFLEX

Several studies were focused on the consequences of reduced PaO2 (hypo xemia) on the Breuer-Hering inspiration-inhibiting vagal reflex. Howev er, these data are often contradictory and do not allow us to decide w hether hypoxemia interacts with the central integration of pulmonary v agal afferents and/or exerts peripheral influence on pulmonary stretch receptor (PSR) activity. The present study was performed in anestheti zed rabbits breathing different gas mixtures containing O-2, N-2 and C O2. Intravenous injection of bicarbonates and CO2 addition in the insp ired mixture maintained pHa and PaCO2 within their physiological range s. The Breuer-Hering reflex, assessed from the changes in diaphragmati c EMG activity, was elicited either by inflating the lungs at differen t volumes above the functional residual capacity (PSR activation) or b y direct electrical stimulation of vagal afferents (central stimulatio n). Hypoxemia never significantly modified the strength of the reflex or its threshold. Thus, acute hypoxemia present at high altitude does not seem to modify the key role played by PSR afferents in the ventila tory control.