Answer
The subject has atherosclerosis; fatty plaques have been laid down in his leg arteries. These vessels are partially occluded and tissues in the area are not getting enough oxygen. There is probably some swelling of the leg tissues. The sympathetic pain receptors are sending pain signals to the to the thalamus via the spinal cord's spinothalamic tract and there is possibly some vasospasm that further decreases the blood flow in the arteries.
Sympathectomy is the severing or deadening of the sympathetic nerve supply to the area in the leg supplied by the occluded artery. This surgery can be done by severing the relevant nerve in the lumbar region or by injecting phenol into the nerve to destroy its ability to transmit neural signals.
This process works because if there is vasospasm this process relieves the vasospasm and improves the blood flow. The main effect is that sympathectomy destroys the ability of the sympathetic nerve to conduct pain signals from the pain receptor to the spinal cord. This means no pain signal can get to the thalamus or to the somatosensory cortex. Therefore, the subject is relieved of pain--for a period. This process does nothing to affect the arterial occlusion and an so blood supply to the region get worsen as the atherosclerosis progresses.
Work Step by Step
Sympathectomy in this case will destroy the sympathetic nerve (in the lumbar region) by which pain sensations are transmitted from the leg to the spinal cord . Consequently no pain sensations can reach the thalamus or the the somatosensory cortex. Therefore, the subject is relieved. The associated decrease in vasomotor tone will abolish any vasospasm and thus there will accrue to the patient the additional benefit of temporary improved blood supply to the area supplied by the occluded artery. Nevertheless, the occlusion remains and will worsen if dietary and medical measures are not taken to treat it.
