Figure 2. Platelet aggregation. Methods: Impedance aggregometry, collagen induced (Collagen I); turbidometry, epinephrine (Epinephrine T); and collagen induced (Collagen T). Mean +/- SEM. Squares = nitroprusside; circles = controls (n = 20, +++P greater or equal to 0.001; nitroprusside vs. control group, *P greater or equal to 0.05 compared with preoperative values).