The purpose of this study is to assess the effect of the spinal cord stimulator (A small wire is surgically implanted under the skin. Low-level electrical signals are then transmitted through the lead to the spinal cord to alleviate pain. Using a magnetic remote control, the patients can turn the current on and off, or adjust the intensity.) on the autonomic nervous system (sympathetic and parasympathetic). Some studies support that the spinal cord stimulation suppresses or decreases sympathetic outflow (the sympathetic nervous system is the one that provide us with the "flight and fight response" and the parasympathetic nervous system is the one that works while we "sleep, rest and digest".). The sympathetic nervous system is important in blood pressure regulation also. However, there are not reports regarding the effect of the spinal cord stimulation on blood pressure regulation in chronic visceral pain patients. Most clinical trials are focus on the effect of the spinal cord stimulation on pain relief. We think we could use blood pressure, heart rate and special analysis of these signals and their relationship to other pain measurements to assess the effect of the spinal cord stimulation in an objective way.