Figure 2. Changes in plasma catecholamine concentrations from prehypoxic values during the hypoxia-30 (PaO230 mmHg), -40 (PaO240 mmHg), and -50 (PaO250 mmHg) periods in the control, clonidine-10, and clonidine-5 groups *P < 0.05 versus the prehypoxic values. (dagger)P < 0.05 versus the control group. (section)P < 0.05 versus the clonidine-5 group.