Fig. 1.

Effects of fentanyl on ventilation. Minute volume is plotted as a function of time after administration of intravenous vehicle or fentanyl (0.0056, 0.0178, 0.056, and 0.178 mg/kg). After a 20-minute baseline period (see Table 1), rats received an intravenous infusion of vehicle or fentanyl (arrow at “0” minutes) followed 5 minutes later by an intravenous infusion of saline (arrow at “5” minutes). Data are presented as a percentage of the average minute volume during the 20-minute baseline period calculated individually for each rat. The inset summarizes the average minute volume during the 5 minutes immediately after infusion of saline or fentanyl (0.0032–0.178 mg/kg), and filled symbols represent doses not shown in the main figure; the gray bar represents the 95% CI for control conditions (i.e., saline infusions at “0” and “5” minutes). Ordinate: minute volume plotted as percent of control and averaged among eight rats ± 1 S.E.M. Abscissae: time in minutes. CI, confidence interval.