Effects of peripheral vasoconstriction on the measurement of blood pressure in a finger.

Using noninvasive techniques only, the fall in mean pressure and the pulse amplification between brachial and finger arterial pressure were measured in six anaesthetised female subjects during surgery. Brachial pressure was measured every 2 min with an oscillometric technique. Finger pressure was measured continuously using an arterial volume clamp method. In addition changes in the degree of peripheral vasoconstriction were established on an adjacent finger with a photo reflection plethysmograph. On the average finger mean pressure is 10 mmHg below brachial pressure. The difference tends to decrease with increasing constriction. The change in the difference between full constriction and maximal dilatation is 8 mmHg. The average finger to brachial pulse amplitude ratio changes from 110% at maximal dilatation to 170% at full constriction. Finger systolic pressure overshoot is responsible for the pulse wave amplification. On the average it is + 7 mmHg and ranges between maximal dilatation and full constriction over 26 mmHg. The standard error deviation on the volume clamp method could be established at 5% for mean pressure, about equal to that of the oscillometric technique in the literature.