BLOOD FLOW AND VASOMOTOR REACTIONS IN THE HAND, FOREARM, FOOT, AND CALF IN RESPONSE TO PHYSICAL AND CHEMICAL STIMULI 1

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Abstract
The blood flow and vasomotor reactions in the hand, foot, forearm and calf were studied by plethysmographic methods. Following strong sensory stimuli, such as pinching the skin until pain is caused, or a sudden, loud noise, the forearm and calf respond in three ways: (1) by a decrease in vol. after a latent period of from 3 to 9 secs.; (2) by an increase in vol. after a latent period usually not exceeding 2 secs.; (3) by a biphasic response with, first, an increase and, subsequently, a decrease in vol. Reasons are stated for the belief that the decrease in vol. is the result of active reflex vasoconstriction, and that the increase in vol. is the result of a passive distension of the vascular bed rather than active vasodilatation. The vessels of the upper part of the body are more sensitive to physical, chemical and nervous stimuli than those of the lower part of the body. Local heat of 43[degree]C. produces nearly complete vasodilatation in the skin, but only relatively slight vasodilatation in the underlying muscles. Exercise is a very effective stimulus for producing vasodilatation in the muscles, but not in the skin. Epinephrin causes a marked decrease in blood flow in the hand and foot and a moderate increase in blood flow in the forearm and calf. The vasoconstrictor effect of epinephrin takes place mainly in the cutaneous vessels, while the blood flow in the muscles is increased. Pitressin produces as marked a decrease in the blood flow in the hand and foot as does epinephrin, and a moderate decrease in the flow in the forearm and calf. The observations of Grant and Pearson, namely, that unless the circulation to the hand is completely obstructed the plethysmographic method of measuring blood flow to the forearm is not accurate under all conditions, has been confirmed.