Fig. 1.
A: typical recordings showing the fentanyl-evoked cardiorespiratory activities and their recoveries. fR, respiratory frequency; VE, minute ventilation. B: typical recordings showing the fentanyl-evoked apneic and cardiovascular responses before (CON) and after perineural treatment of the vagi with capsaicin (pCAP) and subsequent bivagotomy in an anesthetized rat. C: typical recordings of the cardiorespiratory responses to fentanyl before and after perineural treatment of the vagi with vehicle for twice (pVEH1 and pVEH2) in another rat. The traces are arterial blood pressure (ABP), heart rate (HR), and tidal volume (VT). Arrows point to the onset of bolus injection of fentanyl (5.0 μg/kg) into the right atrium.