Fig. 3. Vital signs recorded in 12 healthy volunteers before, during (steps 1–4), and after (postinfusion 1–2) a steady state infusion of saline placebo, dexmedetomidine, and alfentanil are depicted as the mean and the SEM. Dexmedetomidine decreased the systolic and diastolic blood pressures and the heart rate significantly and in plasma concentration dependent fashion compared with saline placebo and alfentanil. There was no difference detected between saline placebo and alfentanil. Alfentanil decreased the respiratory rate and the hemoglobin oxygen saturation significantly and in plasma concentration dependent fashion compared with saline placebo and dexmedetomidine. There was no difference detected between saline placebo and dexmedetomidine.