Ventilatory response to high inspired carbon dioxide concentrations in anesthetized dogs

BACKGROUND: The ventilation ( [Image: see text] ) response to inspired CO(2) has been extensively studied, but rarely with concentrations >10%. AIMS: These experiments were performed to determine whether [Image: see text] 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 [Image: see text] time delays decreased and response magnitude increased with increasing concentrations (p<0.01), but at higher concentrations the time delays were shorter than expected, i.e., 0.5 s to double [Image: see text] at 100% CO(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 [Image: see text] 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.