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Sympathetic Block Does not Reduce Acute Vascular Pain in Humans

e tested the hypothesis that acute experimenW tal pain from blood vessels evoked by a hyperosmolar stimulus is modulated by sympathetic efferent activity. In the case of injured or inflamed tissue, sympathetic efferents apparently affect nociception, because pain is aggravated by noradrenaline and relieved by sympathetic blockade (1). The question of whether such a functional link also exists in normal tissue remains unanswered. It has been denied as regards intact skin (2) but has not been tested for vascular nociception, although this option is likely for two reasons. First, sympathetic efferents and nociceptive afferents are in close proximity in blood vessels (3,4). Second, sympathetic stimulation increases spike activity from other receptors in the vessel wall, e.g., baroreceptors in the aorta and carotid artery (5,6). The sensory innervation of human peripheral veins exclusively subserves nociception (7-9); therefore, veins are particularly well suited to have a sympathetic influence on vascular nociception. Therefore, we studied the effect of sympathetic block (stellate ganglion anesthesia) on pain from hand veins in volunteers.