Digital Rheoplethysmographic Study of the Orienting Reflex in Man

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Abstract
The digital rheo-plethysmograph (RPG) lends itself to many studies of the functions of the central nervous system, particularly the interrelationships of the cardiovascular and nervous systems. Such pehnomena as the effects of sleep, hypnosis and drug actions can be observed through the medium of the digital RPG and the sensitive digital vascular effector organs. The vessels of the finger tip are very sensitive to mild orienting stimuli. The digital vascular reactions to the orienting reflex were studied in response to over 2,000 orienting stimuli in several hundred normal and ill persons. The vascular responses were observed in the finger and toe tips and in the superior portions of the pinnae, being most sensitive in the finger tips and least sensitive in the pinnae. The vasoconstriction not only involved the arterioles and small arteries but also the venules and veins of the digits. Because of the widespread nature of the dermal vasoconstriction, involving all vessels, relatively large shifts of blood must be associated with the reactions. The magnitude and sites of these sudden shifts as well as the influence of the shifts on the function of the cardiovascular system in health and disease remain unknown. The vasoconstrictive responses are interrupted when the sympathetic pathways to the vessels are blocked with procaine.