Electrical stimulation will be performed by 2 stimulation electrodes mounted on proximal to the balloon. Electrical block pulses will be given using a standard electrical stimulator. Single burst pulses will be given with duration of 1ms at 200Hz. The amplitude of the pulses will steadily increase, with steps of 0.5mA and an interval of 15 seconds. For safety, the maximum intensity is limited to 40 mA. ECG monitoring will be performed as a safety measure during the electrical stimulations of the esophagus. Electrical stimulation will be terminated when the subject reached PPT.