title: Ventilatory response to high inspired carbon dioxide concentrations in anesthetized dogs.
abstract: BACKGROUND
  The ventilation (  ) response to inspired CO(2) has been extensively studied, but rarely with concentrations >10%.
  
  
  OBJECTIVE
  These experiments were performed to determine whether  would increase correspondingly to higher concentrations and according to conventional chemoreceptor time delays.
  
  
  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<0.01), but at higher concentrations the time delays were shorter than expected, i.e., 0.5 s to double  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  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.
authors.affiliation: 2725 7th Street South, Cranbrook, British Columbia, V1C 4R8, Canada.
authors.forename: Jack A
authors.initials: JA
authors.lastname: Loeppky
authors.forename: Ray
authors.initials: R
authors.lastname: Risling