Hypoxemia does not affect the strength of the inspiration-inhibiting Breuer-Hering reflex.

Several studies were focused on the consequences of reduced PaO2 (hypoxemia) on the Breuer-Hering inspiration-inhibiting vagal reflex. However, these data are often contradictory and do not allow us to decide whether hypoxemia interacts with the central integration of pulmonary vagal afferents and/or exerts peripheral influence on pulmonary stretch receptor (PSR) activity. The present study was performed in anesthetized rabbits breathing different gas mixtures containing O2, N2 and CO2. Intravenous injection of bicarbonates and CO2 addition in the inspired mixture maintained pHa and PaCO2 within their physiological ranges. The Breuer-Hering reflex, assessed from the changes in diaphragmatic EMG activity, was elicited either by inflating the lungs at different volumes above the functional residual capacity (PSR activation) or by direct electrical stimulation of vagal afferents (central stimulation). 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 ventilatory control.