THE EFFECT OF VENOUS AND ARTERIAL OCCLUSION, AND SYMPATHETIC NERVE TONE, ON DIGITAL BLOOD FLOW 1

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Abstract
Factors responsible for discrepancies between plethysmographic and calorimetric data were investigated. Comparison between arterial and venous obstruction revealed that the latter did not trap all the blood in the digit This factor of deep venous reflux may produce a variable error in the measurement of blood flow plethysmographically. At high rates of flow plethysmographic slopes become less accurate, also reflexes produced by venous obstruction itself or by psychic factors may "break through" the release of sympathetic nerve tone. In addition there may be differences between deep and superficial blood flow and between the circulation in the foot and in the great toe which make comparison between the results of plethysmography and calorimetry difficult. Spinal anesthesia produces no greater release of sympathetic nerve tone in the great toe than indirect heating supplemented by TEAC when blood flow in the skin is measured calorimetrically.