Abstract
Superficial vasomotor tone in the forearm has been thought to be dependent mostly on vasodilatation rather than vasoconstriction. Despite this view we re port now that a mechanism for profound vasoconstriction exists in the forearm surface. This phenomenon was observed in normal subjects undergoing elective radial artery catheterization and the stimulus for the vasoconstriction consisted of the intra-arterial infusion of normal saline (rate of 0.5 - 6.0 ml/min). Two components to this reaction were observed. A stable pericatheter zone of pallor varied in extent proportional to the rate of infusion. The second component consisted of distal patches of vasoconstriction over the whole anterior forearm surface which first appeared 5 to 10 seconds after the infusion rate was in creased. These satellite areas tended to coalesce with sustained infusion but they were unstable over time. Local changes in vascular intrinsic regulation can ac count for the pericatheter vasoconstriction but this does not readily explain the observed distal changes. The time latency, distribution and evolution of the dis tal vasoconstriction suggests the operation of an autonomic vasomotor reflex arc.
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