Effect of altering vasoactivity on the measurement of finger blood pressure

Finapres monitors and oscillometric sphygmomanometers are widely used in blood pressure measurements on the fingers. However, the reliability of finger blood pressure measurement devices still remains a matter of debate.

The volume clamp and modified oscillometric methods for non-invasive beat-to-beat finger mean arterial pressure monitoring are compared during intensive spontaneous changes in vascular tone. The degree of vasoconstriction is established by recording the thumb pulp skin blood flow with a laser Doppler instrument. The oscillometric mean arterial pressure (MAPo) and the Finapres mean arterial pressure (MAPf) are simultaneously recorded from adjacent fingers in eight healthy volunteers in a sitting position at room temperature 22-23 degrees C.

The changes in blood pressure were similarly tracked by the two blood pressure monitors, except the episodes with peripheral vasoconstriction. The difference (MAPo-MAPf) for all simultaneously recorded mean blood pressure values in episodes without vasoconstriction was (mean+/-SD) 0.7+/-1.8mmHg (P=0.33) and in episodes with vasoconstriction 10.6+/-5.6mmHg (P<0.01). A disagreement between the devices during vasoconstriction is assumed to be caused mainly by the tendency of the oscillometric method to overestimate the finger mean blood pressure, and by the tendency of the volume clamp method (Finapres) to underestimate the finger mean blood pressure in condition of peripheral vasoconstriction.

For both types of finger monitors (oscillometric blood pressure devices as well as Finapres or Portapres) it is recommended that intensive vasoconstriction in the subject be avoided during measurements. The presence of acute vasoconstrictions can be determined by simultaneous recording of finger skin blood flow.