THE RELATIVE INFLUENCE OF NERVOUS CONTROL AND OF LOCAL WARMING ON ARTERIOLAR MUSCLE DURING INDIRECT VASODILATATION

Abstract

The relative importance of the inhibition of vasoconstrictor nerves and of concomitant local warming in the production of indirect vasodilatation was investigated in terms of the decrease in critical opening pressure (COP) of digital vessels during body heating. The COP of vessels in a finger of each hand was measured when both hands were kept at about 21 °C during body heating in control experiments and when one of the hands was allowed to warm in air in test experiments. In eight control experiments the COP's of vessels in both fingers fell together. In 25 test experiments they fell together in both fingers until the hand in air began to warm. The COP then fell more rapidly and farther in the finger which warmed. In the test experiments the difference between the reductions in COP in the two fingers was attributed to the effect of local warming. The total reduction in the hand which was prevented from warming was ascribed to inhibition of neurogenic smooth muscle tone. On the average, local warming reduced the COP by 1.3 mm Hg for each increase of 1 °C. Warming occurred when the COP was reduced to about 25 to 35 mm Hg. However, much higher values of COP can exist in the constricted subject. Therefore the initial smooth muscle constricting force may have to be greatly reduced by inhibition of vasoconstrictor nerves before appreciable warming occurs. Then local warming may play an important role in determining the degree of vasodilatation that occurs.