Fig. 2. Percent change in transmitted light through a fingertip (LTF ) of the blocked arm (thick line ) and the unblocked arm (thin line ), and change in systolic blood pressure (SBP ) during stepwise infusion of dexmedetomidine in awake volunteers given axillary brachial plexus block of the left arm. Data are expressed as mean values from all subjects. An increase in transmitted light represents a decrease in finger blood volume (vasoconstriction). The vertical lines  mark the beginning of each step increase in the infusion of dexmedetomidine.