Fig. 2. Systolic blood pressure of control groups ( A ) and prophylactic treatment groups ( B ). After Prehydration = measurement after total prehydration; C < 2.5 = control group with low baseline low-to-high frequency ratio (n = 17); C > 2.5 = control group with high baseline low-to-high frequency ratio (n = 23); C < 2.5, C > 2.5, and T-vasopressor = 500 ml, T-colloid 1,275 ± 250 ml; Colloid 1 = measurement after 500 ml colloid infusion; Colloid 2 = measurement after 1,000 ml colloid infusion; SAB = subarachnoid block; SBP = systolic blood pressure; T-colloid = prophylactic colloid treatment group (n = 20); T-vasopressor = prophylactic vasopressor treatment group (n = 20). Data are presented as mean ± SD. # P < 0.05 versus C > 2.5. + P < 0.05 within group.