Fig. 4. Percent change after the intrathecal injection of 0.25% bupivacaine, levobupivacaine, and dextrobupivacaine. Changes in heart rate in response to the colorectal distension after drug injection were converted to percent change, calculated as (postdrug change/baseline change) × 100%. Data are presented as mean ± SEM (n = 7 in each solution). *  P < 0.05 compared with bupivacaine and dextrobupivacaine.