CONTROL OF PERIPHERAL BLOOD FLOW: RESPONSES IN THE HUMAN HAND WHEN EXTREMITIES ARE WARMED

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Abstract
The blood flows of the hands of 2 lightly-clad men were investigated at ambient temps. ranging from 16 to 30[degree]C by means of 2 plethysmo-calorimeters. One hand was heated to various skin temps. and any alterations in the skin temp. and blood flow on the opposite hand were recorded. Deep tissue temps. indicated that heating and cooling of the respective extremities was not confined to the skin. Further studies were conducted in which either 1 or 2 legs were immersed in hot water (38[degree]C, 40[degree]C, and 42[degree]C) at an ambient temp. of 17.5[degree]C; the effects on hand skin temp. and blood flow were observed. At a steady ambient temp. of 21.5CC or lower, the blood flow in the hand appeared to be dependent upon the over-all need of the body for the conservation or dissipation of heat: whereas in the range 21.5[degree] to 25[degree]C, a delicate vasomotor balance existed and slight additions of heat to one part of the body produced vasodilatation in other parts; at an ambient temp. of 30[degree]C, vasodilatation appeared to be maximal in the unheated hand, although some vasodilatation occurred in the heated hand [probably] as a protective mechanism. It was concluded that under cold ambient conditions (21.5 [degree]Corlower) central mechanisms control peripheral blood flow, whereas in higher temp. ranges local control may become active and indirect vasodilatation may be induced.