Fig. 3. Mean values of the laser Doppler flowmetry signal obtained before and after brachial plexus block. Unstimulated recordings of skin blood flow in the anesthetized arm and contralateral arm are shown in A . Laser Doppler signals from the iontophoresis probes are shown in B . The five horizontal lines in each box plot show the 10th, 25th, 50th, 75th, and 90th percentiles for the anesthetized and contralateral arms. ACh = acetylcholine; AU = arbitrary units; SNP = sodium nitroprusside.