A noninvasive method to assess sympathetic activity

Reflex adjustments of the blood flow through the skin are mediated largely by the sympathetic nervous system and play a fundamental role in the regulation of body temperature. Since blood flow in the digits is almost entirely through skin vessels, surface temperature measurements and digital plethysmography are useful methods of studying the changes in digital blood flow. Sweating is also primarily controlled by the sympathetic system and can be monitored by measuring the electrical resistance of the skin. A noninvasive test to assess sympathetic activity is described comparing the findings in normal subjects and patients with arterial diseases, vasospasm, and diabetes. Digital arteries obstructed by diseases or clot can be delineated from obstruction due to vasospasm, and diabetic neuropathy can be objectively identified. Follow-up studies in more than 1200 patients have demonstrated that an accurate prediction of the outcome of sympathectomy or nonoperative treatment can be made after assessing the results of this safe and inexpensive noninvasive test.