Abstract
The detection of the presence or absence of hyperreactivity of the vasomotor system by the standard cold stimulus used by Hines and Brown and others, 1 depends on statistically significant differences in the arterial blood pressure responses. Although the conclusions of Hines and Brown have been challenged, 2 a systematic study of the vasomotor reactions involved would seem to be desirable for a more complete analysis of the significance and mechanism of the test.
The development of the skin photoelectric plethysmograph 3 offered opportunity to explore the participation of the skin vessels in the responses to the immersion of one hand in ice-cold water. Responses in the finger (recorded with a mechanical plethysmograph), ear and forehead (recorded photoelectrically) have been observed in a random group of 9 normal male subjects (6 whites, 2 Negroes, 1 Chinese) in 24 experiments. The number of observations is too few to bear on the significance of the cold pressor test. They are not offered for that purpose.
Constriction in the finger of the opposite hand was observed in all trials in all subjects. This is a well-known and frequently demonstrated response to the immersion of a limb in cold water. In contrast to the behavior of the finger vessels, the responses in the ear and forehead varied from a slight decrease in blood volume through no effect to an increase in blood volume. Similar changes were observed in the amplitude of the volume pulse. In some cases, a decreased volume pulse was recorded when no decrease in blood volume occurred.
The interpretation of these skin changes as of vasomotor origin is complicated by the fact that the blood content of the skin of the head is readily altered by changes in intrathoracic pressure. The respirations often change considerably as a result of the pain of the test.
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