Sympathetic peripheral vasoconstriction may be measured using an artifact of the Finapres volume clamp technique

OBJECTIVES: The objective of this work was to test the hypothesis that the Finapres underestimates blood pressure during sympathetic peripheral vasoconstriction. METHODS: Measurements were made simultaneously with two Finapres devices and one radial artery tonometer during the onset of periodic lower body negative pressure in healthy volunteers. The Finapres is believed to underestimate blood pressure during sympathetic peripheral vasoconstriction, but tonometry is not considered to be influenced. A lower blood pressure recording was therefore expected from the Finapres during the induced sympathetic vasoconstriction. To test the association with autonomic activity the time course of the difference between the two measurement techniques was compared with the induced change in heart rate. RESULTS: In averaged results from 10 volunteers the Finapres and tonometer both showed a drop in blood pressure with the vacuum onset. A significantly larger drop was recorded by the Finapres. The result is consistent with an underestimate of blood pressure by the Finapres during the autonomic stimulation. The time course of the difference between the two measures of blood pressure follows the induced changes in heart rate, providing further evidence that the differences relate to autonomic activity. CONCLUSION: Measurement of the difference may be a convenient method for monitoring the neurological component of peripheral vasoactivity. It is argued that the difference is insensitive to peripheral vasoactivity mediated by local endothelial or myogenic mechanisms.