Spinal anesthesia induces bradycardia and hypotnesion, because itself decreases parasympathetic activity and increases sympathetic activity. These imbalance of autonomic nervous system can be measured by heart rate variability. Propofol and dexmedetomidine, which are used for sedation during spinal anesthesia, also affect autonomic nervous system, but the exact effects are not well known. The purpose of this study is measuring the effects of propofol or dexmedetomidine on autonomic nervous system in spinal anesthesia.

Spinal anesthesia induces bradycardia and hypotnesion, because itself decreases parasympathetic activity and increases sympathetic activity. These imbalance of autonomic nervous system can be measured by heart rate variability. Propofol and dexmedetomidine, which are used for sedation during spinal anesthesia, also affect autonomic nervous system but the exact effects are not well known. Moreoever, the effect of spinal anesthesia combined with sedation agent on autonomic nervous system has not been evaluated. The purpose of this study is measuring the effects of propofol or dexmedetomidine on autonomic nervous system in spinal anesthesia. The current study is prospective randomized pilot study. Patients are assigned to propofol group and dexmedetomidine group. Using electrocardiaogram analysis, the change of autonomic nervous system will be measured from preoperative to end of surgery.

Inclusion Criteria:

• age 20~60 years old
• Scheduled lower extremity surgery under spinal anesthesia

Exclusion Criteria:

• Arryhthmia
• Uncooperative patients
• Diabetes
• On medication: beta blocker, psychiatric medicine
• Thyroid function abnormality

If a reasonable personal request exist, the investigators can share the data personally.