Measurement of pulsatile limb and finger blood flow by electrical impedance plethysmography: criteria for the diagnosis of abnormal flow.

The range of pulsatile arm and finger blood flow, measured by electrical impedance plethysmography, has been investigated in a hospital ward. The range of absolute blood flows, in ml min-1, was found to be too wide to be used as a standard for identifying single blood flow readings as being abnormal. A blood flow ratio was calculated by dividing the blood flow in the right forearm or middle finger by the blood flow in the left forearm or middle finger. This ratio was found to have a clearly defined range. A blood flow in a unilaterally injured or otherwise abnormal arm or finger was considered to be significantly altered if the blood flow ratio fell outside the previously defined normal range. The diagnosis of significantly altered arm and finger blood flow from abnormalities in the blood flow ratio was tested in a series of experiments, in which artificial changes in upper limb flow were created by high elevation of the right hand. The ratio was measured in 11 patients with unilateral upper limb injuries and in 3 patients who required an urgent assessment of the upper limb circulation. Abnormalities in the ratio were identified in 12 out of 18 subjects after high elevation of the hand and in 8 out of the 14 patients.