Effect of alterations in ambient temperature on blood flow in the skin

The effect of changing ambient temperature on skin temperature was recorded in human subjects; also, its effect on blood flow was measured using venous occlusion and optical plethysmography. When cold stimulus was removed in stages using a heating cabinet, it was found that a biphasic flow response occurred in the fingers with each step change in temperature. There was a rapid transient rise followed by a decline to an equilibrium flow level. The transient rise occurred even when the temperature rose from 37 to 40 degrees C, although at this level the equilibrium remained unchanged. It is suggested that the transient rise was due to stimulation of Hensel's dynamic warmth receptors, whereas the rise in equilibrium temperature was due to removal of cold stimulus, which at low ambient temperatures maintains reflex vasoconstriction through activation of static cold receptors. Upper arm skin responded to removal of cold stimulus by a fall in temperature. Immersion of a different limb in cold water produced vasoconstriction in fingers but vasodilatation in the upper arm skin. It is suggested that this may be due to neurogenic vasodilatation, though the present work gives no indication as to pathways.