Ventilatory response to high inspired carbon dioxide concentrations in anesthetized dogs

Background : The ventilation ( ) response to inspired CO 2 has been extensively studied, but rarely with concentrations >10%. Aims : These experiments were performed to determine whether would increase correspondingly to higher concentrations and according to conventional chemoreceptor time delays. Materials and Methods : We exposed anesthetized dogs acutely, with and without vagotomy and electrical stimulation of the right vagus, to 20-100% CO 2 -balance O 2 .and to 0 and 10% O 2 -balance N 2 . Results : The time delays decreased and response magnitude increased with increasing concentrations (p 2 , with the response to 0% O 2 being ~3 s slower. Right vagotomy significantly reduced baseline breathing frequency (fR), increased tidal volume (VT) and increased the time delay by ~3 s. Bilateral vagotomy further reduced baseline fR and , and reduced the response to CO 2 and increased the time delay by ~12 s. Electro-stimulation of the peripheral right vagus while inspiring CO 2 caused a 13 s asystole and further reduced and delayed the response, especially after bilateral vagotomy, shifting the mode from VT to fR. Conclusions : Results indicate that airway or lung receptors responded to the rapid increase in lung H + and that vagal afferents and unimpaired circulation seem necessary for the initial rapid response to high CO 2 concentrations by receptors upstream from the aortic bodies.