Figure 1.

Breath-by-breath time course plots showing the effects of hypercapnic and hypocapnic CB perfusion on ventilation and the ventilatory response to systemic hypercapnia in two representative dogs

Key transitions are marked by vertical dashed lines; the initiation of perfusion is indicated by a filled arrow. , and for each condition are indicated above each panel. Dog W (upper panels) showed limited response to CB hypo- or hypercapnic perfusion during air breathing. Dog X (lower panels) showed larger responses to CB hypo- or hypercapnic perfusion during air breathing. Note that in both dogs,(a) there was a transient hyper-or hypoventilation in response to CB hypercapnia and CB hypocapnia, respectively (filled arrow and vertical dashed line),(b) after the transient peak or nadir, partial ventilatory compensation occurred (between first two vertical dashed lines in each panel), and(c) the ventilatory responses to increased and systemic hypercapnia (last 3 sections in each panel) were greater in both dogs during CB hypercapnia vs. CB hypocapnia (compare right panel to left panel in each dog after the filled arrow and vertical dashed line).